# Quantum Computing Glossary — Part 1 — A-C

The glossary is too large for a single document (over 3,000 entries), so it is divided into six parts, plus the introduction:

- Quantum Computing Glossary — Introduction.
- Quantum Computing Glossary — Part 1 — A-C. This part.
- Quantum Computing Glossary — Part 2 — D-G.
- Quantum Computing Glossary — Part 3 — H-P.
- Quantum Computing Glossary — Part 4 — Q.
- Quantum Computing Glossary — Part 5 — R-S.
- Quantum Computing Glossary — Part 6 — T-Z.

# Glossary A-C

**|+>.**Superposition of 1/SQRT(2)*(|0> + |1>). See also:*|->*.**|->.**Superposition of 1/SQRT(2)*(|0> — |1>). See also:*|+>*.**|0>.**The*quantum state*which is the*quantum computing*equivalent of a*classical binary 0*. In*ket notation*(*bra-ket notation*.)**|00>.**The*quantum state*of two*qubits*, each of which is in the |0> state. In*ket notation*(*bra-ket notation*.)**|01>.**The*quantum state*of two*qubits*, the first of which is in the |0> state, the second in the |1> state. In*ket notation*(*bra-ket notation*.)**|02>.**The*quantum state*of two*qutrits*, the first of which is in the |0> state, the second in the |2> state. In*ket notation*(*bra-ket notation*.)**|1>.**The*quantum state*which is the*quantum computing*equivalent of a*classical binary 1*. In*ket notation*(*bra-ket notation*.)**|10>.**The*quantum state*of two*qubits*, the first of which is in the |1> state, the second in the |0> state. In*ket notation*(*bra-ket notation*.)**|11>.**The*quantum state*of two*qubits*, each of which is in the |1> state. In*ket notation*(*bra-ket notation*.)**|12>.**The*quantum state*of two*qutrits*, the first of which is in the |1> state, the second in the |2> state. In*ket notation*(*bra-ket notation*.)**|2>.**The third*quantum state*of a*qutrit*. In*ket notation*(*bra-ket notation*.) The three*quantum states*of a*qutrit*being |0>, |1>, and |2>.**|20>.**The*quantum state*of two*qutrits*, the first of which is in the |2> state, the second in the |0> state. In*ket notation*(*bra-ket notation*.)**|21>.**The*quantum state*of two*qutrits*, the first of which is in the |2> state, the second in the |1> state. In*ket notation*(*bra-ket notation*.)**|22>.**The*quantum state*of two*qubits*, each of which is in the |2> state. In*ket notation*(*bra-ket notation*.)**|GHZ>.**See*GHZ state*.**|PHI+>.**Short for*|PHI+> Bell state*.*PHI*is more properly written as the capital Greek*phi*symbol.**|PHI+> Bell state.**Entanglement of 1/SQRT(2)*(|00> + |11>). Abbreviated as*|PHI+>*.*PHI*is more properly written as the capital Greek*phi*symbol. See also:*controlled-NOT gate*and*Bell states*.**|PHI->.**Short for*|PHI-> Bell state*.*PHI*is more properly written as the capital Greek*phi*symbol.**|PHI-> Bell state.**Entanglement of 1/SQRT(2)*(|00> — |11>). Abbreviated as*|PHI->*.*PHI*is more properly written as the capital Greek*phi*symbol. See also:*controlled-NOT gate*and*Bell states*.**|PSI+>.**Short for*|PSI+> Bell state*.*PSI*is more properly written as the capital Greek*psi*symbol.**|PSI+> Bell state.**Entanglement of 1/SQRT(2)*(|01> + |10>). Abbreviated as*|PSI+>*.*PSI*is more properly written as the capital Greek*psi*symbol. See also:*controlled-NOT gate*and*Bell states*.**|PSI->.**Short for*|PSI-> Bell state*.*PSI*is more properly written as the capital Greek*psi*symbol.**|PSI-> Bell state.**Entanglement of 1/SQRT(2)*(|01> — |10>). Abbreviated as*|PSI->*.*PSI*is more properly written as the capital Greek*psi*symbol. See also:*controlled-NOT gate*and*Bell states*.**|W>.**See*W state*.**1-local qubit operator.**TBD.**1-qubit gate performance.**TBD. Referenced indoc from Rigetti Computing. Synonym for*The Quantum Processing Unit (QPU)**single-qubit gate performance*.**1-RDM.**Initialism for*one-particle reduced density matrix*.**1D Fermi-Hubbard model.**Abbreviation for*one-dimensional Fermi-Hubbard model*. Also abbreviated as*1D FHM*.**1D FHM.**Abbreviation for*one-dimensional Fermi-Hubbard model*.**1Q.**Short for*1Q gate*or*one-qubit gate*(*one-qubit quantum logic gate*.)**1Q gate.**Short for*one-qubit gate*(*one-qubit quantum logic gate*.)**2-design.**TBD.**2-local qubit operator.**TBD.**2-qubit gate performance.**TBD. Referenced indoc from Rigetti Computing. Synonym for*The Quantum Processing Unit (QPU)**two-qubit gate performance*.**2-RDM.**Initialism for*two-particle reduced density matrix*.**2Q.**Short for*2Q gate*or*two-qubit gate*(*two-qubit quantum logic gate*.)**2Q gate.**Short for*two-qubit gate*(*two-qubit quantum logic gate*.)**3D quantum integrated circuit.**Synonym for*non-planar quantum integrated circuit*.**3D quantum state.**Short for*three-dimensional quantum state*. Referenced in thearticle.*Team Demonstrates Multiple DOF, Solid-State Quantum Memory***4-bit integer.**Representation of an*integer value*in the range from 0 to 15. See also:*nibble*or*hexadecimal digit*.**8-bit byte.**See*byte*. See also:*8-bit integer*.**8-bit code unit.***Unicode Transformation Format*(*UTF*) for representing*character codes*in either one to four*8-bit integers*.**8-bit integer.**Representation of an*integer value*in the range from 0 to 255. See also:*byte*.**16-bit code unit.***Unicode Transformation Format*(*UTF*) for representing*character codes*in either one or two*16-bit integers*.**16-bit integer.**Representation of an*integer value*in the range from 0 to 65,535. Alternatively, in the range from -32,768 to 32,767.**24-bit integer.**Representation of an*integer value*in the range from 0 to 16,777,215. Alternatively, in the range from -8,388,608 to 8,388,607.**32-bit code unit.***Unicode Transformation Format*(*UTF*) for representing*character codes*as a single*32-bit integer*.**32-bit floating point.**Representation of a*real value*in 32*bits*. See*single-precision floating point*.**32-bit integer.**Representation of an*integer value*in the range from 0 to 4,294,967,295. Alternatively, in the range from -2,147,483,648 to 2,147,483,647.**64-bit floating point.**Representation of a*real value*in 64*bits*. See*double-precision floating point*.**64-bit integer.**Representation of an*integer value*in the range from 0 to 18,446,744,073,709,551,615. Alternatively, in the range from -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807.**80-bit floating point.**Representation of a*real value*in 80*bits*. See*extended-precision floating point*.**AAVQE.**Initialism for*adiabatically assisted variational quantum eigensolver*.**ab initio exciton model.**TBD. Abbreviated as*AIEM*.**absolute value.**The distance from the origin for a*number*,*integer*,*real*, or*complex*. The*magnitude*of a*number*. For*integers*and*reals*, this is simply the*number*without its sign. For a*complex number*it is the square root of the sum of the squares of the*real part*and the*imaginary part*of the*complex number*. See also:*modulus*and*magnitude*. See the Wikipediaarticle.*Absolute value***absolute zero.**The theoretical lowest*temperature*, at which all movement and heat ceases. Zero degrees kelvin — 0.0 K. Not practically achievable, but we can get close, and need to for*superconductor*-based*quantum computing*to work. See the Wikipediaarticle.*Absolute zero***absolutely optimal solution.**See*exact solution*.**absolutely precise solution.**See*exact solution*.**abstract logic.***Logic*in a neutral format which is independent of the specific*code format*or*instructions*needed for*execution*on a particular*computer*, such as an*algebraic expression*in a*high-level programming language*. See also:*intermediate representation*.**AC.**Initialism for*access control*or*alternating current*.**access.**Use of*data*,*programs*, or*systems*. See also:*unrestricted access*,*authorized access*, and*unauthorized access*.**access control.**A*method*for detailing which*users*and*groups of users*will be permitted which type of*access*to particular*items*of*data*,*programs*, or*systems*. See the Wikipediaarticle. Abbreviated as*Access control**AC*. See also:*authorization*.**access controls.**See*access control*. The specific details of permitted access for a particular*user*,*group of users*,*item*of*data*,*program*, or*system*.**accessing quantum hardware remotely.**Since*quantum computers*are expensive and need a special operating environment, it is unlikely that most users will be able to work directly with the*physical machine*. Instead, they will access the machine remotely, over the Internet, either with a*remote login*or via a*cloud-based shared service*.**achievable circuit depth.**The number of*quantum gates*that can be*executed*in a*quantum circuit*on a*quantum computer*before*errors*or*decoherence*distort the result. Synonym for*allowable circuit depth*.**acquire.**See*acquisition*. To buy or lease a*product*, or to subscribe to a*service*.**acquisition.**The*process*used to*acquire*a*product*or*service*. Besides the actual contract to obtain the*product*or*service*, a lengthy*process*of*research*,*evaluation*,*experimentation*,*management review*,*management approval*, and*budget approval*are typically required in many or most*organizations*.**action.**See*activity*. See also:*behavior*and*reaction*.**action on the computational basis.**TBD.**active error correction.**TBD.**activity.**A change in the*state*of a*system*. Alternatively, a sequence of changes, possibly over an extended*period of time*. See also:*event*.**actual classical computer.**See*physical classical computer*, in contrast to a*simulated classical computer*, running on some other*computer*. See also:*real classical computer*or*virtual machine*.**actual computer.**See*physical computer*, in contrast to a*simulated computer*, running on some other*computer*. See also:*real computer*or*virtual machine*.**actual quantum computer.**See*physical quantum computer*, in contrast to a*simulated quantum computer*, running on a*classical computer*. See also:*real quantum computer*.**actual result.**The*result*which actually occurred, in contrast to the*desired result*or*expected result.***adaptive Clifford circuit.**A*Clifford circuit*in which*operations*may be chosen based on*intermediate measurements*of the*outcomes*of previous*operations*, in contrast to a*non-adaptive Clifford circuit*in which the*operations*are fixed and will not vary in response to any*intermediate measurements*. TBD. Referenced in thepaper by Jozsa and Van den Nest.*Classical simulation complexity of extended Clifford circuits***adiabatic process.**A*process*in which*environmental conditions*or inputs are evolving slowly enough that the*system*is able to respond to and adapt to the changing environment and inputs, in contrast to a*diabatic process*in which the*environmental conditions*or inputs change too rapidly for the*system*to respond or adapt, remaining relatively unchanged.**adiabatic quantum annealing.**TBD. See thepresentation by Lucas. See also:*Adiabatic Quantum Annealing Update**adiabatic quantum computation*.**adiabatic quantum computation.**An algorithm to find the optimum for a function using the*quantum adiabatic theorem*. See the Wikipediaarticle. See also*Adiabatic quantum computation**quantum annealing*. Abbreviated as*AQC*.**adiabatic quantum computing.**See*adiabatic quantum computation*.**adiabatic quantum evolution.**TBD.**adiabatic state preparation.**TBD. Abbreviated as*ASP*.**adiabatically assisted variational quantum eigensolver.**TBD. Optimization method. Abbreviated as*AAVQE*.**adiabaticity.**TBD.**adjunct computer.**See*adjunct processor*.**adjunct processor.**See*auxiliary processor*.**adjunct quantum computer.**See*adjunct quantum processor*.**adjunct quantum processor.**The use of a*quantum computer*as an*adjunct processor*or*auxiliary processor*, under the control, direction, and coordination of a*main processor*or*computer*. Even if the*quantum computer*does the bulk of the*computation*, the*main computer*must prepare the*data*, possibly interpret or interact with*intermediate results*of the*quantum computation*, and process the*final results*of the*quantum computation*, which may be only part of the full*computation*.*Coprocesssor*,*auxiliary processor*, and*secondary processor*are synonyms.**adjustable coupling.**TBD.**administrator.**An*individual*responsible for managing logistical aspects of*operations*of an*organization*. May or may not be a*system administrator*. Controls who has what access to various*resources*, such as providing*computing professionals*with*API keys*for*services*.**AFFT.**Initialism for*approximate fast Fourier transform*, but commonly is used as the initialism for*approximate quantum Fourier transform*, which should more properly be abbreviated by the initialism*AQFT*.**AI**. Initialism for*artificial intelligence*.**AIEM.**Initialism for*ab initio exciton model*.**AIEM+MC-VQE.**Abbreviation for combination of*ab initio exciton model*and*multistate, contracted variational quantum eigensolver*.**algebraic calculation.**One or more*algebraic expressions*, with the goal of producing a collection of*real values*,*complex values*,*integer values*, and*non-numeric values*.**algebraic expression.**A variation of a*mathematical formula*constructed using*real values*,*complex values*,*integer values*, or*non-numeric values*,*symbolic values*such as*e*,*h*, and*pi*,*variables*,*algebraic operations*,*trigonometric functions*, other*standard mathematical functions*, and other*functions*, with the goal of producing a*real value*,*complex value*,*integer value or a non-numeric value*.**algebraic operation.**A traditional*mathematical operation*which operates on*real values*,*complex values*,*integer values*, and*non-numeric values*, typically as part of an*algebraic expression*.*Mathematical operations*include addition, subtraction, multiplication, division, exponential, square root, and modulus or remainder, producing a*real value*,*complex value*,*integer value*, or*non-numeric value*. See also:*algebraic expression*.**algorithm.**An abstract conception of processing of*data*to achieve a desired*result*, usually with the intent of*implementing*it with*code*so that it can be executed on a*computer*. Processing typically involves a*sequence of steps*, some of which are*conditional*, and some of which may need to be*repeated*. Algorithms may be named, comparable to the naming of functions in*code*, so that algorithms may be nested and invoked from other algorithms. Algorithms also include methods of representing and organizing data, both input data, intermediate data, and final results or output data. A given desired result may be achieved with any number of distinct algorithms, each of which has its own tradeoffs of complexity, performance, intermediate data requirements, and features. May be a*classical algorithm*designed to execute on a*classical computer*, or a*quantum algorithm*designed to execute on a*quantum computer*. Technically,*algorithms*and*code*are different, although people commonly use them as synonyms. Generally a synonym for*method*.**algorithmic building block.**A combination of*operations*(or*quantum logic gates*) which perform a larger and more abstract*operation*which significantly facilitates development of an*algorithm*. The goal is to reduce an overall*algorithm*or*problem solution*into a relatively smaller number of*algorithmic building blocks*, rather than atomize the*solution*into a large number of individual*operations*(or individual*quantum logic gates*.) Algorithmic building blocks*reduce complexity*by offering*intellectual leverage*and make it easier to design more complex*algorithms*. Reuse of existing algorithmic building blocks can save development time and resources by avoiding*reinventing the wheel*every time a*wheel*is needed. Algorithmic building blocks may come in the form of well-defined functions, macros, or clearly-documented*design patterns*.*Libraries*of algorithmic building blocks can be shared between*projects*and*developers*.**algorithmic complexity.**See*computational complexity*.**all-to-all connectivity.**Any*qubit*can be*connected*(or*coupled*or*entangled*) to any other*qubit*, rather than being restricted, such as only nearest neighbors, for example.**allowable circuit depth.**See*achievable circuit depth*.**alternating current.**The primary form of*electricity*delivered from the*power grid*to*computer systems*, in contrast to*direct current*(*DC*), the form of*electricity*used by*electronic circuits*within*computers*and other*electronic devices*. Abbreviated as*AC*. See the Wikipediaarticle.*Alternating current***ALU.**Initialism for*arithmetic logic unit*. See also:*CPU*.**amorphous.**Lacking a clearly-defined or regular structure or organization, in contrast to a*grid*,*lattice*, or*crystal*. See the Wikipediaarticle.*Amorphous solid***ampere.**The*unit*for*electric current*. The flow of one*coulomb*of*electric charge*per second. See the Wikipediaarticle.*Ampere***amplifier.**Device needed to boost the electrical signal when the*quantum state*of a*qubit*is*measured*, so that it can be processed by*digital circuitry*to be captured as a*binary value*.**amplitude.**See*quantum amplitude*and*probability amplitude*.**amplitude amplification.**See*quantum amplitude amplification*.**amplitude coherence time.**How long a qubit can be expected to remain in the |1> state before decaying to the |0> state. Also known as*energy relaxation time*or*amplitude damping time*. Abbreviated as*T1*. See also:*dephasing time*(*T2*).**amplitude damping.**TBD.**amplitude damping time.**How long a qubit can be expected to remain in the |1> state before decaying to the |0> state. Also known as*energy relaxation time*or*amplitude coherence time*. Abbreviated as*T1*. See also:*dephasing time*(*T2*).**amplitude estimation.**TBD. See thepaper by Brassard, Hoyer, Mosca, and Tapp. See also: a*Quantum Amplitude Amplification and Estimation**mplitude amplification*.**analog computer.**A*computer*whose logic and calculations are based on the*continuous values*of*analog signals*(such as*voltage*or*energy*level) rather than the*discrete values*of*digital bits*or*quantum bits*as in a*digital computer*or a*quantum computer*. See the Wikipediaarticle.*Analog computer***analog quantum computer.**Vague term, but sometimes applied to a*quantum annealing processor*or*adiabatic quantum computing*. Synonym for*quantum analog computer*. See also:*analog quantum computing*.**analog quantum computing.**TBD. Referenced in thepaper by Werbos and Dolmatova. See also:*Analog quantum computing (AQC) and the need for time-symmetric physics**continuous-value quantum computing*.**analog quantum simulation.**TBD. In contrast to*digital quantum simulation*.**analog signal.**An electronic, magnetic, mechanical, or optical*signal*which is interpreted as a*continuous value*of voltage, magnetic flux, mechanical force, or electromagnetic frequency, in contrast to the*discrete value*of a*digital signal*which is interpreted strictly as the*classical binary values*of 0 and 1.**analytical gradient.**TBD. In contrast to a*numerical gradient*.**ancilla qubit.**An additional*qubit*needed either for error correction or to permit a*reversible quantum logic gate*to be used as if a non-reversible, non-quantum*logic gate*, such as to be able to force a*qubit*to a specific value. By definition, all*quantum logic gates*are*reversible quantum logic gates*. See the Wikipediaarticle.*Ancilla bit***ancillas or code qubits.**Additional*qubits*(*ancilla qubits*) used for*quantum error correction*. See also:*code qubit*.**ancilla decoding.**TBD.**ancilla post-selection.**TBD.**angular momentum.**The rotational equivalent of*linear momentum*. see the Wikipediaarticle. See also:*Angular momentum**spin*.**anharmonicity of a qubit.**See*anharmonicity of the qubit*.**anharmonicity of the qubit.**TBD. Referenced indoc from Rigetti Computing.*The Quantum Processing Unit (QPU)***ansatz.**A proposed solution for an equation or optimization problem with the expectation that the proposed solution will be repeatedly evaluated and evolved to incrementally work towards a final, more optimal solution. Maybe a single number or a collection of parameters.**ansatz circuit.**TBD.**ansatz parameter.**One of any number of*parameters*which are required to fully specify an*ansatz*or proposed solution to a problem.**ansatz space.**TBD.**ansatz state.**A*quantum state*which represents an*ansatz*for a problem to be solved. Any required*ansatz parameters*must be realized as*quantum logic gates*to*prepare*the initial*quantum state*of a collection of*qubits*. Also refers to the*final results*after*execution*of a*quantum circuit*intended to evolve the*ansatz*towards a more optimal*solution*.**ansatze.**Plural of*ansatz*. See also:*ansatzes*. More common.**ansatzes.**Plural of*ansatz*. See also:*ansatze*. Less common.**anti-commuting observables.**TBD. Referenced inblog post by Gidney.*Breaking Down the Quantum Swap***antidiagonal.**See*antidiagonal of a matrix*.**antidiagonal of a matrix.**The*entries*of a*matrix*along the*diagonal*from the upper-right corner, in contrast to the*main diagonal*which are*entries*along the*diagonal*from the upper left corner. If the*matrix*is not square,*entries*on the*diagonal*which would be outside the*matrix*will be treated as if they were zero. See the Wikipediaarticle. See also:*Main diagonal**diagonal of a matrix*.**any-to-any.**TBD. As in*any-to-any connectivity*. Abbreviated as*ATA*.**any-to-any connectivity.**Any*qubit*can be*connected*or*coupled*to any other*qubit*— used in a*two-qubit gate*, as opposed to*nearest-neighbor connectivity*or other limits on which pairs of*qubits*can be used in a*two-qubit gate*. Common for*ion-trap quantum computers*, but not for*transmon quantum computers*.**anyon.**A*quasiparticle*which can be used to construct a*topological qubit*and a*topological quantum computer*. See the Wikipediaand*Anyon*articles. See also*Topological quantum computer**quantum braid*.**anyon quasiparticle.**See*anyon*. Redundant since an*anyon*is by definition a*quasiparticle*.**apparatus.**The*hardware*and*equipment*required for a*system*or*experiment*.**API.**Initialism for*application programming interface*.**API key.**A unique*code*, assigned by an*administrator*, which allows a*user*to*access*an*application programming interface*(*API*), such as a*quantum cloud service*or a*remote quantum simulator*.**API spec.**Abbreviation for*API specification*.**API specification.**A document which records the result of*designing*the externally visible*application programming interface*(*API*) for a*system*. Details all aspects of what a*software developer*will see and must know to*program*for the*API*. See also:*detailed specification*,*architecture specification*,*functional specification*,*requirements specification*, and*design specification*. Alternatively, the*API specification*may be included in the*functional specification*for the system. For a*hardware system*, such as a*computer*, a*principles of operation*document would be the equivalent of an*API specification*.**application.**May refer to either*application software*or to the*problem*it addresses.**application developer.***Software developer*focused on*application software*, as opposed to*system software*or*software tools*.**application programming interface.**The ability of*software*to accept requests from other*software*, to perform*functions*, and to retrieve*data*. Abbreviated as*API*. The concept of an*API*applies to both*software libraries*(and*software frameworks*) and*software services*, including*application software*which also offers an*API*. The former uses simple*function calls*to access the*API*directly from the*library*or*framework*while the latter requires*interprocess communication*or use of an*Internet protocol*such as*HTTP*or a*REST API*to indirectly access the*API*.**application programming interface speciation.**See*API specification*.**application software.***Computer software*which addresses some*class of problems*. It is a*solution*or at least part of a*solution*to those*problems*. It may range from a very narrow, niche class to a very broad class.**approximate method.**An approach to a*hard problem*for which an*exact method*is not known or is very difficult, even for a*quantum computer*. Or, the*approximate solution*may be much cheaper than an*exact solution*and deliver acceptable results. See. See also:*Approximation Methods in QM**statistical algorithm*.**approximate quantum computing.***Quantum computers*with*imperfect gates*and*qubits*with limited operability. Alternatively, the use of*statistical algorithms*which produce*approximate solutions*rather than precise or*absolutely optimal solutions*to*problems*, typically motivated by a desire for a faster*solution*, especially for very hard, expensive*problems*, even for a*quantum computer*, but sometimes*algorithms*for precise and absolutely optimal*solutions*are simply not known at this time.**approximate quantum Fourier transform.**Any variation on a*full quantum Fourier transform*which discards some significant fraction of the transform entries since they are relatively small and unlikely to contribute significantly to the final results but would consume a significant amount of computational resources. Abbreviated as*AQFT*, or sometimes*AFFT*. In contrast to a*full quantum Fourier transform*.**approximate solution.***Solution*when an*approximate method*is used to solve a*problem*. See also:*exact solution*,*optimal solution*,*practical solution*.**AQFT.**Initialism for*approximate quantum Fourier transform*. See also:*AFFT*.**arbitrary pair of qubits**. Any two*qubits*in a*quantum computer*without regard to whether they are physically adjacent or have any special relationship. Typically with regard to whether they can be*coupled*or*entangled*. See also:*all-to-all connectivity*.**arbitrary single-qubit states.**A particular*superposition*of the two possible*quantum states*of a*qubit*(*single-qubit states*.)**arbitrary two-qubit states.**A particular*superposition*of the four possible*quantum states*of two*qubits*(*two-qubit states*.)**architecture.**The high-level*design*of a*system*, in contrast to the*detailed design*of the*system*.**architecture specification.**A document which records the result of*designing*the overall*architecture*of a*system*. Details the major*components*and how they interact. See also:*detailed specification*,*functional specification*,*requirements specification*,*API specification*, and*design specification*. A*hardware system*will tend to have both an*architecture specification*and a*principles of operation*document, the latter giving*software developers*all the detail they need to use the*hardware*, but not the detailed internal*implementation*, which they generally will not need.**argument.**See*function argument*.**arithmetic logic unit.**In a*classical computer*, the innermost portion of a*processor*or*central processing unit*where*arithmetic operations*and*logical operations*on*bits*are performed. [TBD: analog for QC — where are logic gates executed?].**array.**Either a linear*list*or a*grid-like*arrangement such as a*matrix*or*lattice*. Either a*data structure*or a*hardware layout*.**artificial intelligence.**See the Wikipediaarticle. Abbreviated as*Artificial intelligence**AI*.**ASP.**Initialism for*adiabatic state preparation*.**assembly language.**A low-level*programming language*of limited expressive power, at the level of the*instructions*of the*instruction set*of the*computer*, in contrast to a*high-level language*with greater expressive power. May refer to a*classical assembly language*or a*quantum assembly language*. See also:*machine language*, which is commonly used as a synonym.**assembly language for quantum computers.**An*assembly language*oriented towards the specialized capabilities and considerations of*quantum computers*. See*quantum assembly language*.**associative access.**Access*data*by its value or a subset of its value, such as a*key*or a*query*. See also:*indirect access*.**associatively access.**See*associative access*.**associatively accessed.**See*associative access*.**asymmetric SQUID geometry.**TBD.**asynchronous.**The ability of an*operation*or*process*to*execute*in parallel with other*operations*and*processes*, in contrast to*synchronous*or*synchronized*.**asynchronous operation.**The ability of an*operation*to*execute*in parallel with other*operations*, in contrast to*synchronous*or*synchronized*.**asynchronous process.**The ability of a*process*to*execute*in parallel with other*processes*, in contrast to*synchronous*or*synchronized*.**ATA.**Initialism for*any-to-any*, as in*any-to-any connectivity*.**atom.**The smallest unit of matter. Composed of*elementary particles*. Can be composed into*molecules*or a*lattice*(*crystal*). Each*atom*has a type or species, known as an*element*, technically*chemical element*, with an*element name*,*element symbol*or*chemical symbol*, and*atomic number*which is the number of*protons*in each*atom*of that*element*.**atomic number.**Number of*protons*in each*atom*of a*chemical element*.**atomic qubit.**A*qubit*consisting or a single atom, such as an*ion trap*, in contrast to a*solid-state qubit*, such as a*silicon spin qubit*.**attribute.**Something about an*entity*which could be enumerated or described. See*quality*,*characteristic*, and*property*. May also be external to the*entity*, such as how other*entities*perceive or otherwise relate to the*entity*.**audio.**Sound. Discrete and continuous sounds, tones, instrumental music, speech, singing, non-verbal oral sounds. Includes directionality of sound. See also:*audio signals*and*audio processing*.**audio capture.**Recording of*audio signals*. May be performed for*audio*alone or in conjunction with*video capture*. Could a*quantum computer*capture*audio signals*with much greater fidelity?**audio processing.**Processing of captured or live*audio signals*. Includes filtering, detection and recognition of sources of sounds, and recognition of speech. Very tedious and*computationally intensive*on a*classical computer*. Potential for acceleration by*quantum computing*, which might open up new avenues of pursuit.*Quantum computing*also has the potential for*continuous processing*rather than only*discrete processing*. See also:*video processing*.**audio signals.**The*waveforms*of*audio*.**augmented Hessian.**TBD.**authorization.**Granting a*user*or*group of users*the right to*access*a particular*resource*. See also:*access control*.**authorized access.**A*user*or*group of users*is granted*access*to some*resource*, in contrast to*unrestricted access*and*unauthorized access*. Technically,*unrestricted access*is implicitly*authorized access*. See also:*authorization*.**automate.**Implement a manual*process*in*software*or even*hardware*.**automaton.**See*automata*.**automata.**See*automata theory*. See also:*quantum automata*.**automata theory.**The concept of a*state machine*which is constructed in such a way that it can recognize a*language*based on its*grammar*. See the Wikipediaarticle. See also*Automata theory**finite-state automaton*.**auxiliary computer.**See*auxiliary processor*.**auxiliary processor.**A*processor*or*computer*which is subservient to and under the control of another*processor*, the*main processor*, or another*computer*, the*main computer*. Synonyms are*adjunct processor*and*coprocessor*. See also:*secondary processor*.**availability.**The*quality*of a*resource*as to whether it physically exists, its*configuration*is set to enable its use, and it is not already in use. See also:*authorization*. Alternatively,*commercial availability*— a*product*or*service*can be purchased, delivered, deployed, and used.**average gate fidelity.**TBD. Referenced indoc from Rigetti Computing.*The Quantum Processing Unit (QPU)***backend.**The*computer*upon which a*quantum program*is to be executed. It may be a*remote quantum computer*, a*local simulator*, or a*remote simulator*.**balance of charge.**An*atom*which has*no net charge*. Alternatively, the exact degree of*imbalance of charge*— count of*protons*minus*count*of*electrons*.**banded quantum Fourier transform.**A variant of the*quantum Fourier transform*(*QFT*) which retains only a subset of the*phase shift gates*, a designated number known as the*bandwidth*, in order to dramatically reduce the*gate count*, which normally scales by n * (n — 1) / 2, but can be reduced to n * m, where n refers to the number of qubits and m refers to the designated bandwidth. See thepaper by Nam and Blümel. Synonym for*Scaling laws for Shor’s algorithm with a banded quantum Fourier transform**narrow-band quantum Fourier transform*.**barren plateau.**TBD.**barren plateau problem.**TBD.**barren plateaus in the cost function landscape.**TBD.**barrier.**An*instruction*in*OpenQASM*which selectively prevents optimization from reordering*logic gates*across the specified barrier. See thepaper.*Open Quantum Assembly Language***base.**See*number base*. See also:*base ten*.**base 10.**See*base ten*.**base ten.**See*decimal numeral system*.**basic Clifford gate.**Either an*H gate*,*T gate*, or*CZ gate*. TBD. Referenced in thepaper by Jozsa and Van den Nest. See also:*Classical simulation complexity of extended Clifford circuits**non-clifford gate*.**basis.**In*linear algebra*, the set of*vectors*, called*basis vectors*, from which all other*vectors*in a*vector space*can be derived, as a*linear combination*of the*basis vectors*. In*quantum mechanics*, the set of*basis states*from which all other*quantum states*of a*quantum system*can be derived, as a*linear combination*of the*basis states*.*Basis states*and*quantum states*are in fact*vectors*,*basis states*are in fact*basis vectors*, and a*quantum system*is in fact a*vector space*. See the Wikipediaarticle.*Basis (linear algebra)***basis change circuit.**TBD.**basis function.**TBD.**basis ordering.**TBD. How*basis vectors*or*basis states*are ordered in a*matrix*.**basis rotation.**TBD.**basis rotation ansatz.**TBD.**basis rotation circuit.**TBD.**basis rotation circuit ansatz.**TBD.**basis rotation circuit fidelity.**TBD.**basis set.**TBD.**basis set function.**TBD.**basis set limit.**TBD.**basis state.**In*quantum mechanics*, a*quantum state*in the*basis*of a*quantum system*. All other*quantum states*in the*quantum system*can be derived as a*linear combination*of the*basis states*.*Basis states*and*quantum states*are in fact*vectors*,*basis states*are in fact*basis vectors*, and a*quantum system*is in fact a*vector space*.**basis vector.**In*linear algebra*, a*vector*in the*basis*of a*vector space*. All other*vectors*in the*vector space*can be derived as a*linear combination*of the*basis vectors*. See also:*basis state*.**bath.**TBD. See also*quantum bath*. Referenced in MITonline course lecture notes.*Quantum Theory of Radiation Interactions***BB84.**A*protocol*for*quantum encryption*developed by Charles Bennett and Gilles Brassard in 1984. See the Wikipediaarticle.*BB84***Beauregard adder.**TBD.**behavior.**The*actions*and*reactions*which can be expected of a*system*.**Bell basis.**TBD.**Bell pair.**See*Bell state*.**Bell state.**Two qubits which are*entangled*. Their collective*quantum state*. Their shared*quantum state.*Alternatively, one of the four possible*Bell states*, corresponding to the four possible combinations of inputs when the*entanglement*is created. See Wikipediaarticle. Also referred to as a*Bell state**Bell pair*or*EPR pair*.**Bell states.**The*quantum state*of two*qubits*which are*entangled*. The mixture or*superposition*of their four individual*states*, two states per*qubit*. Commonly created by using the*controlled-NOT gate*(*CNOT gate*) in conjunction with the*Hadamard gate*(*H gate*) on the*control qubit*to*entangle two qubits*. Four*Bell states*are possible for*entanglement*: 1)*input*of |0> to the*H gate*and target*input*of |0> to the*CNOT gate*produces the*|PHI+> Bell state*— 1/SQRT(2)*(|00> + |11>), 2)*input*of |0> to the*H gate*and target*input*of |1> to the*CNOT gate*produces the*|PSI+> Bell state*— 1/SQRT(2)*(|01> + |10>), 3)*input*of |1> to the*H gate*and target*input*of |0> to the*CNOT gate*produces the*|PHI-> Bell state*— 1/SQRT(2)*(|00> — |11>), and 4)*input*of |1> to the*H gate*and target*input*of |1> to the*CNOT gate*produces the*|PSI-> Bell state*— 1/SQRT(2)*(|01> — |10>). See Wikipediaarticle and*Bell state*.*Todd Brun’s lecture notes, Part-11***Bell’s inequality.**See*Bell’s theorem*.**Bell’s theorem.**Argument that*quantum mechanics*cannot be explained merely by adding*local hidden variables*to*classical mechanics*. See the Wikipediaarticle.*Bell’s theorem***Bernstein-Vazirani algorithm.**TBD. Referenced in, UW-Madison*Riggetti Grove docs*course lecture notes, and*CS 880 — Quantum Information Processing*.*Scott Aaronson Quantum Information Science course lecture notes, Lecture 18***beyond the supremacy regime.**TBD.**Big O.**See*Big-O notation*.**Big O notation.**See*Big-O notation*.**Big-O.**See*Big-O notation*.**Big-O notation.**A simple mathematical formula which roughly approximates or places an upper bound on the resource requirements for an algorithm, typically performance or time. Written as a capital O (big “O”) followed by the formula in parentheses. A way of representing the*computational complexity*of an*algorithm*. For example,*O(n)*for*linear time*,*O(n²)*for*polynomial time*, and*O(2^n)*for*exponential time*. See also the Wikipediaarticle and the*Big O Notation*paper. May also be written as*What Is Quantum Advantage and What Is Quantum Supremacy?**Big O notation*.**binary bit.**The elementary unit of value in a*classical computer*which is either 0 or 1, in contrast to the*qubit*of a*quantum computer*which can be simultaneously in a*superposition*of the |0> and |1> states.**binary computing architecture.**The foundation conception and structure of a*classical computer*in which*computation*is based on the fundamental value unit of a*binary bit*, which has a*value*of either 0 or 1, in contrast to a*quantum computing architecture*, based on*quantum mechanics*, where a*qubit*can be simultaneously in a*superposition*of the |0> and |1> states.**binary code.***Code*which has been*compiled*into*executable code*or an*intermediate representation*.**binary data.***Data*which is*raw bytes*or*raw bits*.**binary integers.**Any two, discrete*integer values*. They could be 0 and 1, or 0 and 100, or -100 and +100, or -1 and -1.**binary value.**A choice between two discrete*values*. 0 or 1. Nothing else and always one or the other. Technically, there is no reason that the two*values*be precisely 0 and 1 — any two*values*will do, and at the lower levels of*hardware*the*values*are real,*physical quantities*, like voltages with thresholds, not clean,*binary integers*. See*binary bit*. See also:*boolean value*.**bipartite entanglement.***Quantum entanglement*of exactly two*qubits*, in contrast to no*entanglement*or*multipartite entanglement*, such as*tripartite entanglement*, involving more than two*qubits*at a time. Alternatively, the*quality*of a*quantum computer*of supporting*entanglement*of only*pairs of qubits*, not more than two*qubits*in a given*entanglement*at a time. Alternatively, the*quality*of a*quantum computer*of supporting*entanglement*of at least*pairs of qubits*and possibly more than two*qubits*in a single*entanglement*. At present, here in August 2018,*current quantum computers*support only*bipartite entanglement*, no more than*pairs of qubits*. [TBD: Whether or to what extent*simulators*support multipartite entanglement]. See thepaper by Qu, Dong, Wang, Bao, Song, and Song. see also:*Bipartite entanglement in AJL’s algorithm for three-strand braids**tripartite entanglement*and*multipartite entanglement*.**bipartite pure state entanglement.**TBD.**bit.**The fundamental value unit of a*computer*, either a*binary bit*for a*classical computer*or a*qubit*for a*quantum computer*. Technically, it could be either, but unless the context is quite clear,*qubit*should be used even when the context is clearly*quantum computing*.**bit-level quantum computer.**A simplified*quantum computer*with only a single*qubit*. Not very useful, except to illustrate the concept of a*quantum computer*or to evaluate the*edge cases*of the*theory of quantum computing*, but lacking*entanglement*since there is no second*qubit*to be*entangled*with.**bit string.**On a*classical computer*, a sequence of*bits*.**blind quantum computing.**TBD. See thepaper by Broadbent, Fitzsimons, and Kashefi. See also:*Universal blind quantum computation**universal blind quantum computation*.**Bloch sphere.**A geometrical representation of the*quantum state*of a*qubit*as one or more*complex vectors*, each with an*amplitude*or*probability amplitude*representing the*probability*that the*quantum system*(*qubit*) is in the particular*quantum state*represented by the particular*complex vector*. Useful for visualizing the underlying*quantum mechanics*of a*qubit*. The horizontal plane represents the X and Y dimensions, X being the*real*part of the*complex vector*and Y being the*imaginary part*. The Z dimension represents a*unit vector*(*magnitude*of 1.0, by definition) for a*pure state*of one of the*basis states*or*basis vectors*, which are |0> and |1> for a*qubit*. In a*pure state*, there will be a single*complex vector*, whose*amplitude*has a*modulus*and*probability*of 1.0, putting it on the surface of the*Bloch sphere*. It may be a*basis vector*(*basis state*) or a rotation of a*basis vector*. By convention the*basis vector*for the |0>*basis state*points to the north pole or positive Z axis of the*Bloch sphere*, and the*basis vector*for the |1>*basis state*points to the south pole or negative Z axis. In a*mixed state*, corresponding to*superposition*of*basis states*, there will be a*complex vector*corresponding to each*basis state*, but with a reduced*amplitude*, such that the sum of the squares of the*modulus*(*magnitude*) of each*complex vector*is 1.0, as required by*unitarity*. Since the*magnitude*of the*complex vectors*for a*mixed state*are less than 1.0, they will be in the interior of the*Bloch sphere*rather than on its surface as for a*pure state*. See the Wikipediaarticle.*Bloch sphere***block.**A group of contiguous*items*which are intended to be treated as a*unit*. See also:*block of code*and*block of storage*.**block of code.**A*block*or group of continuous*operations*,*instructions*, or*statements*to be treated as a single*unit*.*Code*which is to be*executed*at one time. See also:*function*.**block of storage.**A*block*or sequence of contiguous*storage locations*which are commonly accessed and treated as a single*unit*.**Boolean.**See*boolean value*. Capitalized in most contexts since it is based on a name, George Boole.**Boolean algebra.**The*mathematical framework*which formalizes*Boolean logic*. See the Wikipediaarticle.*Boolean algebra***boolean expression.**See*Boolean expression*. Should probably be capitalized, but that’s debatable and optional.**Boolean expression.**See*Boolean logic*.**boolean logic.**See*Boolean logic*. Should probably be capitalized, but that’s debatable and optional.**Boolean logic.**See*Boolean algebra*for the realm of formal mathematics, but more commonly it references the realm of*algorithms*and*code*. Combination of the*Boolean values*of*true*and*false*, the*Boolean operators*,*Boolean variables*,*functions*which return*Boolean values*, and parentheses. May also be extended with*relational operators*. See the Wikipediaarticle, but also see the documentation for the*Boolean algebra**programming language*being used.**boolean operator.**See*Boolean operator*. Should probably be capitalized, but that’s debatable and optional.**Boolean operator.***AND*,*OR*, and*NOT*, or possibly some specialized operators such as*XOR*,*NAND*, and*NOR*. The exact syntax of these operators will vary between*programming languages*, but &&, ||, and ! are common representations. See the Wikipediaarticle, but also see the documentation for the*Boolean algebra**programming language*being used.**boolean value.**See*Boolean value*. Should be capitalized, but uncapitalized is common.**Boolean value.**The*true*and*false*values of*Boolean logic*and*Boolean algebra*.**boolean variable.**See*Boolean variable*. Should be capitalized, but uncapitalized is common.**Boolean variable.**A*variable*holding or intended to hold a*Boolean value*.**Bose-Einstein statistics.**See*boson*. TBD. Beyond the scope of this glossary, for now. See the Wikipediaarticle.*Bose–Einstein statistics***boson.**Any*particle*which obeys*Bose-Einstein statistics*. Not necessarily an*elementary particle*since nuclei of*atoms*with an even*atomic number*can obey*Bose-Einstein statistics*. See also:*photon*and*fermion*. See the Wikipediaarticle.*Boson***boson sampling.**A theoretical approach to*quantum computing*using*photons*and the*linear optical quantum computing*paradigm. See the Wikipediaarticle.*Boson sampling***bound state.**A tendency for a*particle*or*wave*to remain in a localized region of*space*, such as being trapped in a*cavity*. See the Wikipediaarticle. See also:*Bound state**resonator*.**bound system.**TBD. See also:*bound state*.**bounded depth ansatz.**TBD.**bounded-depth devices.**TBD.**bounded-error quantum polynomial time.**Any*problem*which can be*solved*on a*quantum computer*in*polynomial time*correctly at least two-thirds of the time — errors are bounded to no more than one-third of the time. Abbreviated as*BQP*. See the Wikipediaarticle. See also:*BQP**postselected bounded-error quantum polynomial time*or*PostBQP*.**BQP.**Initialism for*bounded-error quantum polynomial time*.**bra.**Used to describe a*quantum state*. The*Hermitian conjugate*of the*ket*of a*bra-ket*. Represents a*row vector*. See*bra-ket notation*. See also:*ket*,*dirac notation*.**bra-ket.**A representation of a*quantum state*in*bra-ket notation*.**bra–ket notation.**Standard notation in*quantum mechanics*for describing the*quantum state*of a*quantum system*, either a specific*quantum state*or the evolution of the*quantum state*under a sequence of*operations*. See the Wikipediaarticle. See also:*Bra–ket notation**bra*and*ket*. Synonym for*Dirac notation*.**branch.**See*branch node*.**branch node.**A*node*in a*graph*, especially a*tree*, which has relationships to other*nodes*as being subsidiary to the*branch node*, in contrast to a*leaf node*. See also*root node*.**Brillouin condition.**TBD.**brute force.**Any approach to any*problem*which is based on*exhaustive enumeration*of all possibilities rather than focusing in a directed manner towards a*solution*.**brute-force.**See*brute force*.**brute-force algorithm.**Any*algorithm*which finds a*solution*to a*problem*by*exhaustively enumerating*all possibilities, in contrast to a*formula*or*heuristic*which proceeds directly towards the solution. See also:*brute-force attack*and*brute-force search*. Synonym for*brute-force method*.**brute-force approach.**See*brute-force algorithm*.**brute-force attack.**Attempting to guess a password or other*phrase*using a*brute-force algorithm*.**brute-force calculation.**See*brute-force algorithm*.**brute-force method.**See*brute-force calculation*.**brute-force search.**Finding a*value*in a*list*or other*data structure*by incrementally checking every entry in the list or structure. Alternatively, finding a*solution*to a*problem*by*exhaustively checking*every possible*solution*. See the Wikipediaarticle. Synonym for*Brute-force search**exhaustive search*.**brute force simulation strategies.**A*simulation*based on a*brute-force approach*of exhaustive enumeration of all possibilities.**budget approval.**The*process*of getting*management*to sign off on the cost of an*acquisition*of a*product*or*service*. See also:*management review*and*management approval*.**built-in gate.**A*quantum logic gate*(*operation*) which is predefined in the*QASM quantum assembly language*. In contrast to a*user-defined gate*. See thepaper.*Open Quantum Assembly Language***bus.**A*connection*or set of*connections*, between multiple*components*which facilitate the transfer of a significant amount of*data*between*components*, either due to parallel*connections*or to high speed on a single*connection*. Generally,*bus*refers to a*classical bus*, as described here, or a*quantum bus*for controlling and interconnecting*qubits*, such as using*microwaves*. Can be applied to*software*, but generally refers to*hardware*. Alternatively, a reference to a*bus bar*for transfer of*electrical power*. See also:*interconnection*.**bus bar.**A very robust*connection*between a*power source*and some number of*hardware components*which require*power*.**business.***Organization*whose*mission*revolves around generating a financial profit.**business value.***Utility*and*value*of an*entity*, such as a*product*or*service*, to an*organization*, which may or may not necessarily be a*business*.*Business value*may be financial, but could be about creating*opportunity*, or simply satisfying a need.**business-relevant quantum computer.**A*quantum computer*capable of supporting*applications*which directly benefit the operations of a*business*, such as*design*,*development*,*production*, and*delivery*of*products*and*services*. Likely relevant also to other*organizations*of comparable complexity.**byte**. On a*classical computer*, may be interpreted either as an*8-bit integer*, a*character code*(or one*byte*of a*multi-byte character code*), or as simply eight*bits*. Synonym for*8-bit byte*. At present, there is no support for the*quantum*equivalent of a*byte*, a*qubyte*, on any*current quantum computer*or*near-term quantum computer*.**C.**Abbreviation for*complex number*. More correctly, the set of all*complex numbers*. Also abbreviated as*c-number*.**C classical programming language.**An old programming language for*classical computers*designed for both a reasonable level of expressiveness in terms of algebraic expressions, control structures, and data structures but also for maximum efficiency and performance by exploiting the*hardware*features of*classical computers*. See also:*quantum C language*.**C language.**See*C classical programming language*.**C programming language.**See*C classical programming language*.**c-number.**Abbreviation for*complex number*. Also abbreviated as*C*.**CA.**Initialism for*cellular automaton*.**cable.***Wiring*used to establish a*connection*between*computers*or*devices*. Could be a*fiber optic cable*.**cabling.**See*cable*.**calculate.**See*calculation*.**calculation.**Determination of the*value*of some*quantity*by evaluating a*formula*, such as a*mathematical calculation*or an*algebraic calculation*. Alternatively, the*value*which resulted from performing a*calculation*.**calibration.**See*physical qubit calibration*. See also:*recalibration*.**camera.**A*device*for capturing*photographic images*, either a*digital camera*or an old-fashioned*camera*which captures*images*on film. Alternatively, a*video camera*.**canonical quantum algorithms.**Vague term which generally refers to any and all well-known*quantum algorithms*, such as*Shor’s algorithm*and*Grover’s algorithm*.**capability.**A*quality*,*capacity*, or*function*of a*system*or*device*, including*hardware*,*computing systems*,*computer programs*, and other*software*. See also:*function*,*feature*, and*capacity*.**capacitance.**The amount of*energy*or*charge*which a*capacitor*is capable of storing. See the Wikipediaarticle.*Capacitor***capacitive coupling.**TBD. See also:*fixed capacitive coupling*.**capacitively coupled semiconductor spin qubits.**TBD.**capacitor.**An*electronic component*capable of storing and releasing*energy*or*charge*. See the Wikipediaarticle. See also:*Capacitor**capacitance*and*inductor*.**capacity.**The amount of*code*and*data*which a*system*or*device*can handle, including*hardware*,*computing systems*,*computer programs*, and other*software*. Alternatively, simply a synonym for*capability*.**capture and control atomic ion qubits.**TBD.**cat state.**A*quantum system*or*qubit*which is in a*superposition*of two distinct*quantum states*at the same time. [TBD: two or more states?]. A tribute to*Schrödinger’s cat*. See the Wikipediaarticle.*Cat state***cat states.**(plural) An*entangled*set of*qubits*, analogous to a single*qubit*in the*cat state*. See also:*four-qubit cat state*and*Bell state*.**cat state preparation.**Sequence of*quantum logic gates*that will initialize one or more*qubits*into a*cat state*. The simplest sequence being an*H gate*followed by a*CNOT gate*. See also:*Bell state*.**category.***Criteria*for distinguishing*entities*. Synonym for*class*and*type*.**causation.**The notion that every*effect*must have a*cause*, although it may not always be clear what that*cause*is.**cause.**A*force*or*action*which*results*in an*effect*, such as a*force*acting on an*object*.**cause and effect.**See*causation*.**cavity.**See*resonator*. A*device*for trapping a*photon*.**cavity bus.**The use of a*resonator*(*cavity*) to transmit*energy*,*state*, or*information*between two*devices*, one or both of which may be*qubits*. See also:*readout resonator*and*coupling resonator*. See thepaper by Majer, Chow, Gambetta, Koch, Johnson, Schreier, Frunzio, Schuster, Houck, Wallraff, Blais, Devoret, Girvin, and Schoelkopf.*Coupling Superconducting Qubits via a Cavity Bus***cavity QED.**See*cavity quantum electrodynamics*.**cavity quantum electrodynamics.**The use of*light*trapped in a*cavity*to implement a*qubit*. TBD. See the Wikipediaarticle. Also referred to as*Cavity quantum electrodynamics**cavity QED*.**CCNOT.**See*controlled-controlled-NOT gate*. Synonym for*CCNOT gate*.**CCNOT gate.**See*controlled-controlled-NOT gate*.**cell.**A relatively small, localized*unit*of*processing*which focuses on the*environment*immediately surrounding the*cell*. Can also*communicate*with nearby as well as distant*cells*. See also:*cellular automaton*and*quantum cellular automaton*.**cellular automata.**Plural of*cellular automaton*.**cellular automaton.**A model of*computing*based on a*grid*or*lattice*of small*processors*, called*cells*, each of which*evolves*its*state*based on the configuration of the*states*of the adjacent*cells*. See the Wikipediaarticle. See also:*Cellular automaton**quantum cellular automaton*. Abbreviated as*CA***central processing unit.**The*main processor*of a*computer system*, where the bulk of*computation*is performed. Abbreviated as*CPU*. See also*arithmetic logic unit*.**certainty.**The*quality*that an*outcome*will indeed occur, or has indeed already occurred, or that a*result*will be as expected or already has been as expected, in contrast with*uncertainty*. A*classical computation*will tend to have the*quality*of*certainty*, while*uncertainty*and*probability*are more characteristic of*quantum systems*and*quantum computations*. See also:*deterministic*.**chaos theory.**Study and modeling of*dynamic systems*. See*classical chaos theory*or*quantum chaos theory.*See the Wikipediaarticle.*Chaos theory***character.**A simple*symbol*corresponding to a single*mark*, such as a letter, digit, or punctuation. See also:*string*,*character string*,*text*.**character code.**The*integer value*assigned to a*character*. Traditionally, this was an*8-bit integer*, but with the advent of*Unicode*,*16-bit integer*,*24-bit integer*, and even*32-bit integer*codes are possible. Codes larger than a single*8-bit integer*are represented as*multi-byte character codes*. See also:*code point*.**character sequence.**See*character string*.**character string.**A*sequence of characters*. Synonym for*string*or*text*. Alternatively, a*storage location*in which a*character sequence*can be*stored*and manipulated.**characteristic.**A*quality*of an*entity*. May be of utility in identifying the*type*or*identity*of an*entity*.**charge.**See*electric charge*. See also:*net electric charge*and*charged particle*.**charged particle.**See*ion*. A*particle*which has a*net electric charge*.**charge qubit.**A*qubit*which is based on the*electric charge*of*Cooper pairs*and a*Josephson junction*. A*Cooper pair*is a*charged particle*, two*electrons*. This requires*superconductivity*, so all*charge qubits*are*superconducting charge qubits*, by definition, at least at this time. Also known as a*transmon*. See the Wikipediaand*Transmon*articles. See also:*Charge qubit**superconducting charge qubit*. Other types of*qubit*include*flux qubit*,*phase qubit*, and*spin qubit*.**chemical accuracy.**TBD.**chemical bond.**A persistent attraction between two or more*atoms*or*molecules*which keeps them bound as a single*molecule*. See the Wikipediaarticle.*Chemical bond***chemical compound.**A combination of two or more*chemical elements*, either discrete*atoms*or composite*molecules*, as a result of the formation of one or more*chemical bonds*during a*chemical reaction*.**chemical element.**A type or species of*atom*, based on its number of*protons*— its*atomic number*, with a*name*—*element name*, and a*symbol*—*chemical symbol*. Synonym for*element*. See also:*chemistry*.**chemical reaction.**An interaction between some combination of*atoms*and*molecules*which results in either the formation or elimination of one or more*chemical bonds*, producing one or more*molecules*as a result.**chemical symbol.**A one or two character*symbol*for a*chemical element*. Usually an abbreviation of its*element name*, but sometimes an abbreviation of its classical rather than modern*element name*.**chemistry.**The studical of*chemical elements*and*chemical compounds*, their properties, how they form*chemical compounds*or*molecules*and how*atoms*and*molecules*interact (*chemical reaction*.) See the Wikipediaarticle.*Chemistry***chemistry simulation.**Using*quantum computing*to simulate complex (or simple)*molecules*and*reactions*in*chemistry*.**chimera graph.**A*graph*which is relatively sparsely*connected*. The connectivity model for*qubits*on the D-Wave*quantum computers*. See thepaper by Cao, Jiang, Perouli, and Kais and the*Solving Set Cover with Pairs Problem Using Quantum Annealing*graph paper by Xu, Sun, Wu, Zhang, Arshed, and Sanders. See also:*Quantum walk on a chimera**direct embedding*.**chip.**See*integrated circuit*. May be either the*integrated circuit*itself or the*chip package*.**chip design.**The logical and physical structure and layout or arrangement of*electronic components*on an*integrated circuit*(*IC*,*chip*.) Alternatively, the*process*of deciding what*electronic components*will be placed on an*integrated circuit*, how they will be connected, and how they will connect to the world outside of the*integrated circuit*. Includes extra*electronic components*and connections to facilitate testing.**chip layout.**See*chip design*. Both the actual*design*and the*process of*design.**chip package.**The packaging used to contain, protect, and connect an*integrated circuit*to a*printed circuit board*. Ambiguous whether the*integrated circuit*or the total*chip package*is the*chip*.**Church’s thesis.**The assertion that all computing devices can be simulated by a Turing machine. That’s for all*classical*computing devices, but does not include*quantum*computing devices.**circuit.**See*quantum logic circuit*. Alternatively,*classical logic circuit*.**circuit ansatz.**TBD.**circuit board.**Short for*printed circuit board*.**circuit depth.**The number of*quantum logic gates*in a*quantum logic circuit*. Synonym for*quantum logic circuit depth*,*gate count*, or*quantum logic gate count*.**circuit execution.**May be either*quantum circuit execution*or*quantum program execution*. May be referred to as simply*execution*.**circuit generation.**See*quantum logic circuit generation*.**circuit fidelity.**See*quantum logic circuit fidelity*.**circuit step.**See*quantum logic circuit step*.**circuitry.**See*electronic circuitry*and*digital circuitry*.**circularly polarised microwave.**TBD. Referenced in thepaper by Nagata, Kuramitani, Sekiguchi, and Kosaka.*Universal holonomic quantum gates over geometric spin qubits with polarised microwaves***circulator.**See*quantum circulator*. Controls flow of*microwave signals*in a*quantum computer*.**class.**A set of criteria for distinguishing a subset of*objects*from all other*objects*. Synonym for*type*and*category*. See also:*class of objects*,*hierarchy of classes*, and*OOP class*.**class of objects.**All*objects*which meet the criteria for inclusion in a specified*class*. See also:*OOP class*.**class of problems.**A collection of*problems*which have enough in common that a*solution*to one*problem*will be a*solution*to all*problems*in the class.**classical.**Traditional approaches and methods, such as*classical mechanics*and*classical computing*, in contrast with approaches which break with tradition, such as*quantum mechanics*and*quantum computing*.**classical algorithm.**An*algorithm*designed to be executed on a*classical computer*.**classical assembly language.***Assembly language*for a*classical computer*, in contrast to*higher-level programming languages*and*quantum assembly language*for a*quantum computer*.**classical binary.**See*classical binary value*. Having a traditional*binary value*, either of two*states*or*values*.**classical binary 0.**The*classical binary value*of 0. In contrast to the*quantum state*of |0>.**classical binary 1.**The*classical binary value*of 1. In contrast to the*quantum state*of |1>.**classical binary value.**0 or 1. Nothing else and always one or the other. See*binary value*. In contrast to the*quantum states*of |0> and |1>.**classical bit.**A*bit*on a*classical computer*, which has a*value*of either 0 or 1, in contrast to a*quantum bit*or*qubit*, whose*value*may be a*superposition*of 0 and 1, or |0> and |1>, technically . See*binary bit*.**classical bus.**A*connection*or set of*connections*, between multiple*hardware components*which facilitate the transfer of a significant amount of*data*between*components*, either due to parallel*connections*or to high speed on a single*connection*. For a*quantum computer*, see*quantum bus*for controlling and interconnecting*qubits*, such as using*microwaves*. See also:*interconnection*. See the Wikipediaarticle.*Bus (computing)***classical chaos theory.***Chaos theory*studies and models the behavior of*dynamic systems*, in a classical, rather than*quantum*sense. See the Wikipediaarticle. See also:*Chaos theory**quantum chaos theory*.**classical code.***Software*, a*program*, or*instructions*as*implementation*of an*algorithm*designed to*execute*on a*classical computer*, in contrast to*quantum code*designed to*execute*on a*quantum computer*. See also:*classical program*.**classical component.**A*component*other than a*qubit*. Any*component*of a*classical computer*or*classical device*. Any*component*other than one which is unique to a*quantum computer*.**classical computation.***Software*running on a*classical computer*.*Computation*based on*classical code*which implements*classical algorithms*operating on*binary bits*, running on a*classical computer*, in contrast to*quantum computation*which is based on*quantum code*which implements*quantum algorithms*operating on*quantum bits*(*qubits*), which follow from the*principles of quantum mechanics*, running on a*quantum computer*. There is one exception:*quantum code*can be run on a*quantum simulator*, running on a*classical computer*, in which case this is true*quantum computation*rather than*classical computation*, although the simulator itself is in fact*classic computation*.**classical computational chemistry.***Computational chemistry*performed on a*classical computer*. In contrast to*quantum computational chemistry*.**classical computer.**A*traditional digital computer*whose architecture is based on*binary bits*, in contrast to a*quantum computer*which is based on*quantum bits*(*qubits*) which follow from the*principles of quantum mechanics*.**classical computer engineering.**Traditional*computer engineering*as applied to the design and construction of the*hardware*for*classical computers*, in contrast to*quantum computer engineering*for*quantum computers*. See also:*classical computer science*.**classical computer science.**Traditional*computer science*as applied to the theory, design, development, and application of*classical computer software*on*classical computers*, in contrast to*quantum computer science*for*quantum computers*. See also:*classical computer engineering*.**classical computer simulation.***Software*which allows a*computer*to simulate a particular type of*classical computer*, in contrast to a*quantum computer simulation*.**classical computing.**The use or operation of a*classical computer*with*classical storage*,*classical programming*, and*classical programming languages*with*classical data structures*and*classical control structures*. As well as*user interface (UI)*interaction. And all of the activities associated with using a*classical computer*, as well as the*classical computing ecosystem*.**classical computing ecosystem.**The*computing ecosystem*for*classical computing*. The technology, tools, support infrastructure, vendors, component suppliers, service providers, community, and people. And of course the*classical computers*themselves.**classical computing limit.**The*theoretical*and*practical*limits for*performance*and*capacity*of*computations*on*classical computers*. Not well-characterized at the present time. Essentially only a vague notion rather than a hard limit since*classical computers*continue to grow in*performance*and*capacity*, as does the cleverness of our*architectures*and*algorithms*.**classical control flow.**See*classical control structures*.**classical control structures.***Control structures*used in a*classical programming language*to program a*classical computer*. This includes conditional execution (if), repetition (loops), and nesting (blocks, function calls, and user-defined functions.) Not relevant to a*quantum program*on a*quantum computer*, but still relevant for*hybrid mode of operation*.**classical data structures.***Data structures*used in a*classical programming language*to program a*classical computer*. This include*arrays*,*matrices*,*lists*,*trees*,*tables*,*databases*, user-defined*classes*of*objects*, etc. Not relevant to a*quantum program*on a*quantum computer*.**classical device.**Any*device*other than one which is unique to a*quantum computer*. Anything but a*qubit*, generally.**classical digital logic circuit.**An*electronic circuit*using*classical digital logic components*. See*classical logic circuit*.**classical digital logic components.**See*classical logic gate*.**classical host computer.**The*computer*on which a user runs the*software*(*host program)*that interfaces remotely to a*quantum computer*. By definition, the user is running on a*classical computer*. Synonym for*host computer*.**classical host program.**The*software*(*host program)*which a user runs on their computer which interfaces remotely to a*quantum computer*. By definition, the user is running on a*classical computer*. Synonym for*host program*.**classical host program and computer.**The*software*and*hardware*which a user uses to interface to a*quantum computer*. See*classical host program*and*classical host computer*.**classical instruction set.**See*classical instruction set architecture*.**classical instruction set architecture.**A*detailed specification*of the*instruction set architecture*of a*classical computer*, which is the set of*operations*or*instructions*that a*classical computer*can*execute*, including any internal data and control resources, such as*registers*and*memory*which can be*accessed*by those instructions, as well as any*data formats*which are relevant to both instructions and internal data and control resources. Both overview and details for an*instruction set architecture*would be found in a*principles of operation*document. See also*quantum instruction set architecture*.**classical level.**Portions of a*computation*which*execute*on a*classical computer*, while other portions of the same overall*computation*execute directly on a*quantum computer*. See*hybrid mode of operation*.**classical logic**. Any combination of*operations*(*classical operations*) designed to perform some*computation*, ranging from a single*operation*, to a sequence of*operations*,*statements*and*expressions*in a*high-level language*, to an entire*block*or*function*, or even an entire*program*. In contrast to*quantum logic*. In a*high-level language*the logic is expressed in*expressions*and*statements*, including*function calls*. Alternatively, a synonym for*classical logic gate*and*classical logic circuit*.**classical logic circuit.***Classical hardware*. A collection of*classical logic gates*and other*electronic components*as well as their*interconnections*.**classical logic gate.**A*physical logic gate*which performs a*logic operation*directly in hardware. In contrast to a*quantum logic gate*which is a specification of a*quantum logic operation*to be performed rather than its physical realization.**classical logic operation.**In contrast to a*quantum logic operation*. AND, OR, NOT, XOR, etc.**classical mechanics.**See*Newtonian mechanics*.**classical operation.**Any operation which can be performed by a*classical computer*. This includes arithmetic, bit manipulation,*(classical) logical operations*, and control flow. In contrast to*quantum operation*.**classical post-processing.**See*post-processing*. Redundant since all*post-processing*is performed on a*classical computer*.**classical program.**A*computer program*for a*classical computer*.**classical programming language.**A*programming language*used to develop*programs*for a*classical computer*, including*classical data structures*and*classical control structures*, in contrast to a*quantum programming language*.**classical/quantum.**Relating to the*hybrid mode of operation*. See thepaper by Smith, Curtis, and Zeng of Rigetti Computing.*A Practical Quantum Instruction Set Architecture***classical/quantum algorithm.**An*algorithm*based on the*hybrid mode of operation*. See thepaper by Smith, Curtis, and Zeng of Rigetti Computing.*A Practical Quantum Instruction Set Architecture***classical quantum chemistry.**TBD.**classical/quantum computation.**A*computation*based on the*hybrid mode of operation*. See thepaper by Smith, Curtis, and Zeng of Rigetti Computing.*A Practical Quantum Instruction Set Architecture***classical and quantum future.**See*quantum and classical future*. The emphasis is intended to be on*quantum computing*.**classical register.**A*register*or*device*on a*classical computer*which is capable of representing a single*value*at any given moment, in contrast to a*quantum register*, which can represent all possible*values*at every moment.**classical simulability.**Whether a*quantum algorithm*or*quantum circuit*can be simulated on one or more*classical computers*in any reasonable amount of time, or even ever. See also:*quantum supremacy*.**classical state.**The essential quantities or qualities which define and describe the character of a*system*. See the Wikipediaarticle. May or may not describe all of the fine detail of the*State (computer science)**system*. For example, the*classical state*of a*bit*is 0 or 1, despite the details of voltage and current which are used to achieve that state. May simply be enough to recreate or restore the*system*. See also:*quantum state*and*state of matter*.**classical storage.**How data is stored and accessed in a*classical computer*, including*memory*and*mass storage*(disk, tape, etc.) See also:*storage*.**classical structures.**Either*classical control structures*or*classical data structures*, or some combination thereof. The*code*and*data*of a*classical computer program*. Not present in a*quantum computer*(*quantum processor*), but relevant for the*hybrid mode of operation*.**classical system.**A*traditional computing system*. A*computing system*based on*traditional digital computing*. In contrast to a*quantum system*.**classical uncertainty.**TBD. See also:*uncertainty principle*and*Heisenberg’s uncertainty principle*.**classical value.**Any*value*which is supported by a*classical computer*, both*numeric values*and*non-numeric values*, in contrast to*quantum value*. Alternatively the*binary value*of a*bit*, either 0 or 1, in contrast to the*quantum value*of a*qubit*which may be a*superposition*of 0 and 1, or |0> and |1>, technically.**classically intractable.**There is no known*practical solution*for a*problem*at this time using*classical computers*. It is either not theoretically possible to*develop*an*algorithm*for a*solution*on a*classical computer*, or even if an*algorithm*can be*designed*, it would more*resources*—*time*and*storage*— than is readily available or economically feasible. If a*solution*is possible using a*quantum computer*, this would constitute a*quantum advantage*.**classically intractable regime.**TBD.**classically intractable subroutine.**TBD. A*quantum circuit*is*executed*as if it were a*subroutine*called from a larger*classical algorithm*. The expectation is that there is no*tractable classical implementation*which is functionally equivalent to the*quantum circuit*.**classically simulate.**Simulate a*quantum circuit*or*quantum program*on a*classical computer*using a*quantum simulator*.**classically simulate a quantum computer.**Use or run a*quantum simulator*on a*classical computer*.**Clifford circuit.**A sequence of one or more*quantum logic gates*operating on one or more*qubits*whose effect on the*quantum state*of those*qubits*can be expressed as a sequence of*basic Clifford gates*. A*Clifford circuit*consisting solely of*basic Clifford gates*is a*unitary Clifford circuit*. TBD. Referenced in thepaper by Jozsa and Van den Nest. See also:*Classical simulation complexity of extended Clifford circuits**adaptive Clifford circuit*and*non-adaptive Clifford circuit*.**Clifford computation.**TBD. Referenced in thepaper by Jozsa and Van den Nest.*Classical simulation complexity of extended Clifford circuits***Clifford computational task.**TBD. Referenced in thepaper by Jozsa and Van den Nest.*Classical simulation complexity of extended Clifford circuits***Clifford gate.**Either a*basic Clifford gate*or a*gate*whose effect on the*quantum state*of*qubits*can be expressed using only*basic Clifford gates*— either an*H gate*,*T gate*, or*CZ gate*. TBD. Referenced in thepaper by Jozsa and Van den Nest. See also:*Classical simulation complexity of extended Clifford circuits**non-clifford gate*.**Clifford group.**TBD. See thepaper by Helsen, Wallman, Wehner.*Representations of the multi-qubit Clifford group***Clifford operation.**See*Clifford circuit*. TBD. Referenced in thepaper by Jozsa and Van den Nest. See also:*Classical simulation complexity of extended Clifford circuits**n-qubit Clifford operation*and*non-Clifford operation*.**cloud based quantum computing.**See*cloud-based quantum computing*.**cloud-accessible device.**TBD.**cloud-based computing service.***Computing*offered as a*cloud-based service*.**cloud-based quantum computing.**A*computing service model*in which a user can design and develop a*quantum program*on their own personal computer, a*classical computer*, but*execute*the program on either a*real quantum computer*, or on a*high-end quantum computer simulator*, which is maintained in the cloud as a shared resource for many users over the Internet. The user’s*program*will be uploaded to the*quantum cloud service*, where it will be queued up for*execution*on a*real quantum computer*, or on a*high-end quantum simulator*, when it becomes available, and any*final results*from*program execution*returned to the user upon completion of*quantum execution*. For example, the.*IBM Q Experience***cloud-based quantum computing service.***Quantum computing*offered as a*cloud-based computing service*. See*cloud-based quantum computing*.**cloud-based service.**Any*service*offered over the Internet, where the*software*for the service runs on*servers*in the*cloud*. See also*cloud-based computing service*.**cloud-based shared service.***Cloud-based service*where limited resources must be shared among potentially many users using a*queued-work model*.**cluster state.**TBD.**cluster-state computer.**TBD.**cluster-state model.**TBD.**CNN.**Initialism for*convolutional neural network*. See also:*QNN*—*quanvolutional neural network*.**CNOT.**See*controlled-NOT gate*. Synonym for*CNOT gate*.**CNOT gate.**See*controlled-NOT gate*. Synonym for*CNOT*.**CNOT operation.**See*controlled-NOT gate*. Synonym for*CNOT gate*.**co-design.**See*codesign*. See also:*quantum codesign*.**coaxial cable.**Electrical*cable*used to deliver*microwave pulses*to a*qubit chip*to control the*quantum state*of the*qubit*. One per*qubit*. Although nominally an*electrical cable*, with two copper*conductors*, the function of*coaxial cable*is the transmission of*electromagnetic radiation*, specifically*radio frequency*(*RF*) signals, which includes*microwaves*. See the Wikipediaarticle.*Coaxial cable***code.***Software*, a*program*,*statements*,*instructions*or*operations*to be*executed*on a*computer*as the*implementation*of an*algorithm*. See also:*design and code*. May be*classical code*for a*classical computer*or*quantum code*for a*quantum computer*. Alternatively, a*code*is a*data value*or*pattern*of*data values*which have a particular meaning, such as a*code qubit*or a*character code*.**code analysis tool.**A*development tool*which provides*software developers*with statistical and specific information about their*code*, such as what it actually does, what it doesn’t do, what side effects it might have, as well as suggestions for improvement.**code or data format.**See*data format*and*code format*. May represent*code*or may represent*data*. At some levels,*code*and*data*are both simply*data*.**code format.**See*data format*.*Code*is simply another form of*data*, either as*text*for*source code*or*binary data*or*binary code*for*compiled code*.**code fragment.***Source code*which is only a portion of a complete*program*or maybe only a portion of a complete*function*. A*sequence of instructions*or*sequence of operations*or*sequence of statements*. May represent an interesting portion of an*algorithm*. For a*quantum computer*this would constitute a*quantum logic circuit*or possibly only a portion of a*quantum logic circuit*.**codesign.**Collaborative*design*with the intention of achieving a much more optimal overall*design*. Such as designing*algorithms*and the*hardware*on which those*algorithms*will run at the same time to to achieve a more optimal*design*for both, feeding knowledge about the*algorithms*into*design*of the*hardware*and knowledge about the*hardware*into*design*of the*algorithms*, as well as feedback loops between both*design*processes. See also:*quantum codesign*. Also written as*co-design*.**coding.**The activity of writing*code*. May or may not include some degree of*designing*. May or may not include development of new*algorithms*, or simply use existing*algorithms*. See also*designing and coding*.**code block.**See*block of code*.**code point.**A*character code*in*Unicode*.**code qubit.**Additional*qubits*(*ancilla qubits*) used for*quantum error correction*.**code unit.**The*units*for representing*code points*(*character codes*). Many*code points*may fit in a single*code unit*, but some may two or more*code units*. See*8-bit code unit*,*16-bit code unit*, and*32-bit code unit*. See also:*multi-byte character codes*.**coefficient vector.**TBD.**coherence.**See*quantum coherence*.**coherence monotones.**TBD.**coherence time.**See*quantum coherence time*— the*elapsed time*before a*qubit*or a*quantum computer*loses*coherence*— the*quantum state*of*qubits*begins to deteriorate. Synonym for*decoherence time*. Referenced indoc from Rigetti Computing. See also:*The Quantum Processing Unit (QPU)**amplitude coherence time*or*T1*and*dephasing time*or*T2*.**coherent control.**Control or manipulation of the*quantum state*of a*quantum system*(even a single*qubit*) using an external field such as a laser pulse or*microwave pulse*. See the Wikipediaarticle.*Coherent control***coherent error.**TBD.**coherent state.**TBD.**collapse.**See*collapse of quantum state on measurement*.**collapse of quantum state on measurement.**Any attempt to*observe*or*measure*the*quantum state*of a*quantum system*or*qubit*will cause the*wave function*of the*quantum state*to collapse to the*measured state*, which is equivalent to its measured*classical value*. It no longer has a*quantum value*. See also:*wave function*.**collapse of wave function.**See*collapse of quantum state on measurement*.**collapse of wave function on measurement.**See*collapse of quantum state on measurement*.**column.**The horizontal*dimension*of a*table*or*matrix*.*Data*or*information*is*organized*vertically as*rows*in a*column*. See also:*row*.**column matrix.**See*column vector*.**column vector.**A*vector*which is an*n*x 1*matrix*, one column wide but*n*rows vertically. A*column vector*can be*transposed*to form a*row vector*, and vice versa. See the Wikipediaarticle. See also*Row and column vectors**row vector*,*ket*. Synonym for*column matrix*.**combined error mitigation.**TBD.**commercial availability stage.**The stage of*development*of a*technology*where the*research stage*,*experimental stage*, and*product development stage*have been completed and*products*based on the*technology*are now ready for*real-world applications*.**commercial development of quantum applications.**TBD. Referenced inbill.*National Quantum Initiative Act***commercial problem.**A*problem*which is relevant to commercial entities — businesses.**commercially available classical computer.**See*commercially-available classical computer*.**commercially-available classical computer.***Classical computer*which is readily available from*vendors*today. Excludes*experimental*,*research*, and*theoretical**computers*.**commercially available quantum computer.**See*commercially-available quantum computer*.**commercially-available quantum computer.***Quantum computer*which is readily available from*vendors*today. Excludes*experimental*,*research*, and*theoretical**computers*.**commercially relevant quantum computer.**See*commercially-relevant quantum computer*.**commercially-relevant quantum computer.**The stage at which*quantum computing*becomes relevant to a broad swath of*commercial problems*, rather than only extreme, niche applications. The stage at which an average large company could expect to be able to buy and maintain a*quantum computer*at a reasonable price and be able to assign a relatively average and easy to assemble team of*application developers*to develop relatively sophisticated*quantum computing solutions*, rather than requiring an elite team of super-experts, or to be able to buy off the shelf, packaged solutions to relatively common business problems. Alternatively, cloud-based quantum computing services are readily available at a reasonable price.**commercially-viable quantum computer.**Synonym for*commercially relevant quantum computer*. Also, from the perspective of the vendor, revenues from sales, leases, and services for their*quantum computers*will yield a healthy per-unit profit margin as well as quickly recoup the full research and development cost, and ongoing profits will fully fund ongoing research and development for next generation quantum systems on a sustainable basis for many years to come.**commercially-viable quantum computing.**See*commercially-viable quantum computer*.**common format.**A*code or data format*which is shared by more than one*tool*or*application*.**commonly used quantum gate.**See*commonly used quantum logic gate*.**commonly used quantum gate library.**See*commonly used quantum logic gate library*.**commonly used quantum logic gate.**As*quantum computing*is such a new and unsettled field, not all*quantum computers*share the exact same*quantum instruction set*(*quantum logic gates*), but there are a number of*quantum logic gates*which are reasonably common and widely supported on most*quantum computers*. These are the*commonly used quantum logic gates*.**commonly used quantum logic gate library.**A*quantum logic gate library*for the*commonly used quantum logic gates*, organized in a form to facilitate the*development*,*compilation*, and*execution*of*quantum programs*using those*gates*.**compensate.**See*compensation*.**compensation.**Capability of*mitigating*,*correcting*, partially*mitigating*, or in some way responding in at least a somewhat positive manner to some*event*or*conditions*which have been*detected*. Such as*errors*—*error detection*and*error correction*. See also:*detection*and*mitigation*.**compilation.**See*compilation of a program*.**compilation of a program.***Transformation*of*source code*into*executable code*using a*programming language compiler*. See also:*interpreter***compilation of quantum programs.**See*compilation of a program*.**compiled code.**See*binary code*or*code format*. The result of*processing*of*source code*by a*compiler*. See also:*intermediate representation*.**compiler.**See*programming language compiler*.**complete quantum entanglement.**Redundant — simply*quantum entanglement*. It’s all or nothing. [TBD: verify]**complex.**Either a reference to having a*high complexity*, or a reference to a*complex number*.**complex number.**A*number*which has both a*real part*and an*imaginary*part. Central to*quantum mechanics*, and hence central to the function of a*quantum computer*and*quantum states*in particular. See the Wikipediaarticle. Abbreviated as*Complex number**c-number*or*C*. See also:*real number*,*integer number*,*absolute value*, and*modulus*.**complex plane.**TBD.**complex value.**A*value*which is a*complex number*. On a*classical computer*this is a pair of*real values*, one for the real part of the complex number and one for the imaginary part. [TBD: QC?]**complexity.**The level of intricacy of a*system*or any portion thereof. How many*components*it has, their*complexity*, how many*connections*they have, and how many*relationships*they have, among any number of other issues which can complicate understanding and control of the*system*. See also:*high complexity*.**component.**A smaller part of a larger whole. The parts, pieces, or units which are needed to construct a*system*,*subsystem*, or*device*. Generally, either a*hardware component*or a*software component*.**component failure.**A*component*either produces*errors*, malfunctions, is unavailable, or is completely unable to*function*at all. See also:*fault tolerance*.**component physical system.**TBD.**component system.**TBD.**composed.**Constructed using*composition*.**composite physical system.**TBD.**composite quantum system.**TBD.**composite state.**Mathematically combining two or more*states*into a single*state*, such as the*quantum states*of two*qubits*to*execute*a*two-qubit quantum logic gate*.**composite system.**TBD.**composition.**The*process*of constructing a*system,**subsystem*, or*component*from smaller*components*,*hardware*or*software*.**computable function.**TBD. In contrast to a*non-computable function*.**computation.**The processing of*data*to achieve a*desired result*, according to one or more*algorithms*, using*code*or*software*packaged as a*program*,*executing*on a*computer*. This can involve*classical computation*on a*classical computer*or*quantum computation*on a*quantum computer*, or*hybrid computation*, part*classical*and part*quantum*.**computational.**Relating to*computation*.**computational basis.**The full set of*computational basis states*(*pure states*) for a single qubit, two un-entangled qubits, two entangled qubits, an n-qubit register, or all qubits of an n-qubit quantum computer. All of the*quantum states*which can be*measured*(*observed*.)*Superposition*of*quantum states*cannot be directly*observed*or directly*measured*. Synonym for*computational basis states*, plural.**computational basis measurement.**TBD.**computational basis state.**A*pure state*which is part of the*computational basis*for a qubit, subset of qubits, or all qubits of a quantum computer. |0> and |1> for a single qubit, |00>, |01>, |10>, and |11> for two un-entangled qubits, |00> and |11> or |01> and |10> for two entangled qubits (Bell states), or |x1 x2… xn> for xi = 0 and 1 for an n-qubit register or an n-qubit quantum computer — although it gets more complicated if xi and xj are entangled.*Superposition*does not affect the*computational basis states*— the full*quantum state*(*wave function*) for one or more qubits is a*linear combination*of*computational basis states*. Each of the terms of the*wave equation*for a single qubit, two un-entangled qubits, two entangled qubits, a qubit register, or all qubits of a quantum computer is a discrete*computational basis state*, separate from the*amplitude*for each term in the*wave function*.**computational chemistry.**TBD. See*classical computational chemistry*and*quantum computational chemistry*. See the Wikipediaarticle.*Computational chemistry***computational chemistry package.**TBD.**computational complexity.**An approximate sense of how much*computing resources*will be required for an*algorithm*to handle*input data*of various sizes or values, particularly*time*and*memory*. See also:*polynomial time*and*exponential time*. Also referred to as*algorithmic complexity*. See also*Big-O notation*. See also the Wikipediaand*Computational complexity*articles and the*Computational complexity theory*paper.*What Is Quantum Advantage and What Is Quantum Supremacy?***computational complexity theory.**An approximate sense of how much*computing resources*will be required to*solve*a*problem*given*input data*of various sizes or values, particularly*time*and*memory*. Similar to*computational complexity*, but focuses on the nature of the*problem*being*solved*rather than a particular*algorithm*to*solve*the*problem*. See also the Wikipediaand*Computational complexity*articles.*Computational complexity theory***computational entity.**An*entity*within a*computer system*, including*data*,*data structures*,*control structures*,*functions*,*programs*,*quantum logic gates*,*quantum logic circuits*,*software components*,*subsystems*, and*systems*.**computational environment.***Data*and*control structures*immediately surrounding and near a*computational entity*. The*context*in which a*computation*is being*executed*or in which*data*or*code*resides. See also:*physical environment*.**computational hardness.**TBD.**computational Hilbert space.**TBD.**computational qubit.**Synonym for*logical qubit*.**computational variety.**Design of a*system*or*application*which utilizes different forms of*computing hardware*, particularly*classical computing*,*quantum computing*,*graphical processing units*(*GPUs*),*field-programmable gate arrays*(*FPGAs*),*full-custom integrated circuits*, or other forms of*custom hardware*, separately or in some, hybrid, combination. See thereport from Accenture.*Embracing computational variety***computer.**A*system*or*device*which can be*programmed*to accomplish some*task*through the*execution*of a*sequence of steps*or*operations*or*instructions*, known as a*computer program*. May be a*classical computer*or a*quantum computer*.**computer engineer.**An*electrical engineer*or*computer scientist*who specializes in the conception, architecture, design, and*implementation*of the*hardware*of*computers*. See also:*software developer*.**computer engineering.***Design*and*development*of the*hardware*for a*computer*,*classical computer engineering*for a*classical computer*and*quantum computer engineering*for a*quantum computer*. See also:*computer science*.**computer professional.**Individual with specialized education, training, knowledge, experience, and judgment in some aspect of*computing*. Commonly a*software developer*or*computer engineer*.**computer program.***Code of software*which has been packaged to*execute*as a*unit*, in a*process*, on a*computer system*. Abbreviated as*program*. Each*program*which is*executing*on a*computer system*will*execute*within a distinct*process*— multiple*programs*means multiple*processes*.**computer programmer.**See*programmer*and*software developer*.**computer programming.**See*programming*.**computer science.***Theory*,*design*,*development*, and*application*of the*software*for a*computer*,*classical computer science*for a*classical computer*and*quantum computer science*for a*quantum computer*. See also:*computer engineering*.**computer scientist.**A scientist specializing in*computing*, especially*algorithms*and*systems*of*computers*.**computer software.**See*software*. Any*software*needed to use a*computer*to solve*problems*.**computer system**. Either a synonym for*computer*or a*computer*combined with any additional*devices*or equipment needed to support the operation of the*computer*. May or may not include the*computer software*which may be needed to use the*computer*in order to solve*problems*.**computing.**The use or operation of a*computer*, including*design*,*development*, and*execution*of*computer software*as well as operation of the*physical computer*itself. As well as*user interface (UI)*interaction. And all of the activities associated with using a*computer*, as well as the*computing ecosystem*.**computing ecosystem.**The technology, tools, support infrastructure, vendors, component suppliers, service providers, community, and people involved in any way with the conception, design, production, use, and support for*computing*. And of course the*computers*themselves.**computing needs.**What*tasks*a*user*or*customer*wishes to accomplish, or what*goals*they wish to achieve which require*computation*. See also:*computing tasks*.**computing service model.**A*computing model*where a*user*on their own*computer*remotely connects over the Internet to a*computing service provider*who maintains*servers*which can satisfy the*computing needs*of the*user*on demand. The*provider*will allocate resources as needed and when available, freeing them up for other*users*when they are no longer needed.**computing service provider.**A*vendor*who maintains any number of*servers*on the Internet which can be made available, on demand, for*customers*or*users*needing to perform*computing tasks*but not wanting to acquire and maintain servers of their own. These servers could be, and generally are,*classical computers*, but may be*quantum computers*as well, or*high-end quantum computer simulators*. Abbreviated to*provider*.**computing tasks.**Actions and activities required to complete a c*omputation*, including the*computation*itself. Efforts required to satisfy*computing needs*.**concentric transmon.**See*concentric transmon qubit*.**concentric transmon qubit.**TBD. See thepaper by Braumüller, Sandberg, Vissers, Schneider, Schlör, Grünhaupt, Rotzinger, Marthaler, Lukashenko, Dieter, Ustinov, Weides, and Pappas.*Concentric transmon qubit featuring fast tunability and an anisotropic magnetic dipole moment***concept.**An idea,*theory*, or*design*, independent of whether it has been*realized*in the*real world*.**conception.**See*concept*.**conceptual approach.**The essence of an*approach*, independent of the detail needed to actually pursue that*approach*. A high-level*approach*.**conceptualize.**To take a vague idea and flesh it out into a more credible and complete*concept*. See also:*conceptual approach*,*imagine*,*formulate*, and*theorize*.**condition.**Some*event*or*data value*or*pattern*of*events*or*data values*which is of interest for some reason and worthy of a response if*detected*. See also:*detection*,*mitigation*,*correction*, and*compensation*. Alternatively,*environmental conditions*.**conduction.**See*conduction of electricity*.**conduction of electricity.**See*flow of current*.**conductor.**A*material*which facilitates the*transmission*of an*electric charge*, in contrast to an*insulator*which inhibits the*transmission*of an*electric charge*.**conductor of electricity.**Anything which is a*conductor*.**conducting material.**A*material which is a conducting medium*.**conducting medium.**A*medium*, such as a*solid*, which is a*conductor of electricity*.**conductivity.***Quality*of a*conductor*.**configuration parameter.**Any*information*other than actual*input data*which is used to*control*or affect a*system*,*device*,*application*,*software component*,*process*, or*computer program*. Synonym for*configuration setting*.**configuration setting.**See*configuration parameter*.**conjugate transpose.**TBD. Referenced in thepaper by Shor.*Polynomial-Time Algorithms for Prime Factorization and Discrete Logarithms on a Quantum Computer***connect.***Execution*of a*quantum logic operation*which causes two*qubits*to become*connected*(*entangled*.) See*connectivity between qubits*. Alternatively,*connect*between*classical components*.**connected.**Two*qubits*whose*quantum states*are*entangled*. See*quantum entanglement*and*connectivity between qubits*. Alternatively,*classical components*which are*connected*.**connected qubits.**Two*qubits*whose*quantum states*are*entangled*. See*quantum entanglement*. Alternatively, one or more pairs of*qubits*which are*connected*(*entangled*.) See*connectivity between qubits*. Also referred to as*entangled qubits*or*pair of qubits*or*qubit pair*.**connection.**A pathway for*energy*,*electricity*, or*data*between two or more*components*. Both*hardware*and*software*. May be used for either*power*,*control*, or*data*. May or may not have a direction or be bidirectional.*Connections*can be*photonic*or*wireless*in addition to*electrical*or*electronic*. See also:*interconnection*and*bus*.**connectivity.**The potential for*pairs of qubits*to become*connected*(*entangled*.) See*connectivity between qubits*. Alternatively,*connectivity*between*classical components*.**connectivity between qubits.***Quantum entanglement*between a pair of*qubits*. Alternatively, any number of*pairs of qubits*, where the*quantum state*of each pair is*entangled*. Alternatively, the degree to which all possible pairs of*qubits*in a*quantum computer*can be connected (*entangled*), from*minimally connected*to*partially connected*to*fully connected*. See also:*connectivity map*.**connectivity map.**A*specification*of which*pairs*of*qubits*can be*entangled*(*coupled*.) There may be*hardware*restrictions which do not allow all pairs to be*entangled*. There may be further restrictions on which*qubits*can be the*control qubit*for a given*target qubit*, and vice versa. Each*design*of*quantum computer*is different. Synonym for*coupling map*. See also:*connectivity between qubits*. See thepaper by Wang, Li, Yin, and Zeng.*16-qubit IBM universal quantum computer can be fully entangled***constant.**Something which does not change, such as a*state*,*environmental condition*, or*value*. See also:*mathematical constant*and*symbolic constant*.**constraint.**See*requirement*. A*criteria*or*condition*which is expected or required to remain true.**constructive interference.**TBD. In contrast to*destructive interference*.**contemplate.**Consider and ponder an*entity*,*real*or*imagined*. See also:*imagine*and*theorize*.**context.***Location*and*conditions*immediately surrounding and near an*entity*. See also:*environment*.**continuous.**Proceeding through*time*or*space*without gaps or*discrete*steps, in contrast to*discrete*. Alternatively, a*phenomenon*or*system*which*evolves**continuously*, in contrast to*evolving*in*discrete steps*.**continuous interval of time.**A period of time. All*moments of time*in that*interval*.**continuous level.**The level of some*quantity*is*continuous*, rather than*discrete*.**continuous period of time.**See*continuous interval of time*.**continuous process.**See*continuous processing*.**continuous processing.**Processing which occurs at all*moments of time*, in contrast to*discrete processing*which occurs at*intervals of time*.**continuous quantum variable.**TBD. Referenced in thepaper by Travaglione and Milburn.*Preparing encoded states in an oscillator***continuous signal.**A*signal*which has*continuous values*, such as a*voltage*, in contrast to a*discrete signal*or a*digital signal*.**continuous-time quantum walk.**TBD. In contrast to a*discrete-time quantum walk*. See the Wikipediaarticle.*Quantum walk***continuous value.**A*quantity*which does not require*discrete*steps, such as a*voltage*or*energy*, in contrast to*discrete values*where there is a clear and discernible distinction between adjacent or successive values, such as a*digital signal*. See also:*analog signal*.**continuous-value quantum computing.**TBD. Referenced in thepaper by Werbos and Dolmatova. See also:*Analog quantum computing (AQC) and the need for time-symmetric physics**analog quantum computing*.**continuous variable.**A*quantity*which takes on a smooth spectrum of values, in contrast to a*discrete variable*which takes on a very limited number of values, with clear gaps between the values. Abbreviated as*CV*. See also:*continuous value*.**continuous-variable quantum computation.**TBD. Referenced in thepaper by Humphreys, Kolthammer, Nunn, Barbieri, Datta, and Walmsley. Shortened as*Continuous-Variable Quantum Computing in Optical Time-Frequency Modes using Quantum Memories**CV quantum computation*. See also:*continuous-variable quantum computing*and*continuous-value quantum information*.**continuous-variable quantum computing.**TBD. Referenced in thepaper by Humphreys, Kolthammer, Nunn, Barbieri, Datta, and Walmsley. Shortened as*Continuous-Variable Quantum Computing in Optical Time-Frequency Modes using Quantum Memories**CV quantum computing*. See also:*continuous-value quantum computation*and*continuous-value quantum information*.**continuous-variable quantum information.**TBD. Referenced in thepaper by Humphreys, Kolthammer, Nunn, Barbieri, Datta, and Walmsley. Shortened as*Continuous-Variable Quantum Computing in Optical Time-Frequency Modes using Quantum Memories**CV quantum information*. See also:*continuous-variable quantum computation*and*continuous-value quantum computing*.**continuum quantum computer.**A particular characterization of*quantum computers*by physicist Stephen Blaha. See thepaper. Unclear if this has any general acceptance.*A Quantum Computer Foundation for the Standard Model and SuperString Theories***contrived application.**An*application*which was conceived for some purpose other than to solve a*real-world problem*, in contrast to a*real-world application*. See also:*toy application*.**control.**The ability to cause or prevent some activity or*state change*of some*component*or*entity*.**control and construct quantum systems.**Able to demonstrate the ability to manipulate the*quantum state*of some*physical device*sufficiently well to create working*qubits*and to assemble a meaningful number of those*qubits*into a working*quantum computer*. Referenced innews release.*NSF launches effort to create first practical quantum computer***control logic.***Code*, a*host program*, running on a*host computer*, a*classical computer*, which supervises, monitors, and controls the*execution*of a*quantum program*on a*quantum computer*or a*quantum simulator*. A given*quantum logic circuit*must*execute*on its own to completion, but there may be more than one*circuit*or more than one*iteration*of the same*circuit*needed for the full*computation*, the full*solution*to a*problem*. Or, errors may occur and the host program may need to re-*execute*the*circuit*. The*control logic*may also make modifications or additions to a*circuit*for successive*iterations*, including changes to the*preparation logic*(*quantum logic circuit preparation*) which initializes the*quantum state*of the*qubits*. Alternatively, the*digital logic circuits*within a*quantum computer*which control and directly interface with the*qubits*and interface them to the outside world.**control pulse.**TBD.**control qubit.**A specified*qubit*in a*quantum logic gate*which must be in the |1>*state*in order for the*function*of the*quantum logic gate*to be performed. See also:*CNOT gate*,*CZ gate*, and*CSWAP gate*.**control structures.**See*classical control structures*.*Quantum computers*do not, at present, have*control structures*per se. Any control needs to be done at the*classical level*or as a*hybrid mode of operation*.**controlled (cX cY cZ) gate.***Quantum logic gate*(*operation*) which*flips*the*quantum state*of a specified*qubit*about the specified axis if the*control qubit*is in the*one state*, |1>. [TBD: is a pure |1> required or is control probabilistic?]. See the Wikipediaarticle. See also:*Quantum logic gate**controlled-X gate*,*controlled-Y gate*, and*controlled-Z gate*.**controlled-controlled-NOT gate.**A*three-qubit gate*which complements (*flips*) the*quantum state*of a third*qubit*if the first two*qubits*are in the |1>*state*. [TBD: is a pure |1> required or is control probabilistic?]. This is equivalent to applying the*X gate*, conditionally. See*Toffoli (CCNOT) gate*. Abbreviated as*CCNOT*.**controlled-controlled-NOT operation.**See*controlled-controlled-NOT gate*.**controlled multiplication gates.**TBD. Referenced in thepaper by Beauregard.*Circuit for Shor’s algorithm using 2n+3 qubits***controlled-NOT gate.***Quantum logic gate*(*operation*) which*flips*the*quantum state*of a specified*qubit*(the target*qubit*) if and only if another specified*qubit*(the*control qubit*) is in the*one state*, |1>. This is comparable, loosely, to the Boolean*NOT*operation.*Flipping*is equivalent to the*X gate*. Commonly used in conjunction with the*Hadamard gate*(*H gate*) on the*control qubit*to*entangle two qubits*. Four*Bell states*are possible for*entanglement*: 1)*input*of |0> to the*H gate*and target*input*of |0> to the*CNOT gate*produces the*|PHI+> Bell state*— 1/SQRT(2)*(|00> + |11>), 2)*input*of |0> to the*H gate*and target*input*of |1> to the*CNOT gate*produces the*|PSI+> Bell state*— 1/SQRT(2)*(|01> + |10>), 3)*input*of |1> to the*H gate*and target*input*of |0> to the*CNOT gate*produces the*|PHI-> Bell state*— 1/SQRT(2)*(|00> — |11>), and 4)*input*of |1> to the*H gate*and target*input*of |1> to the*CNOT gate*produces the*|PSI-> Bell state*— 1/SQRT(2)*(|01> — |10>). Abbreviated as*CNOT*or*CNOT gate*. Synonym for*controlled-X gate*(*CX gate*) and*CNOT operation*. See the Wikipediaarticle.*Quantum logic gate***controlled-NOT operation.**See*controlled-NOT gate*.**controlled phase gate.**A collection of four*quantum logic gates*which apply a controlled*phase*to a*qubit*based on the*quantum states*of both the target*qubit*and the*control qubit*. [TBD: verify, and is it a phase shift or an absolute phase?.] See*CPHASE gate*,*CPHASE00 gate*,*CPHASE01 gate*,*CPHASE10 gate*, and*CPHASE11 gate*. Referenced infrom Rigetti Computing. See the*Source Code Documentation — pyquil.api*paper by Qin, Wang, Miranowicz, Zhong, and Nori. See also:*Heralded quantum controlled phase gates with dissipative dynamics in macroscopically-distant resonators**heralded quantum controlled phase gate*.**controlled-X gate.**See*CX gate*. See also:*CNOT gate*and*controlled-NOT gate*.**controlled-Y gate.**See*CY gate*.**controlled-Z gate.**See*CZ gate*.**conventional computer.**Synonym for*classical computer*. In contrast to a*quantum computer*.**convolutional neural network.**TBD. Abbreviated as*CNN*. See also:*quanvolutional neural network*.**Cooper pair.**A pair of electrons which are bound together at ultra-low temperatures and are responsible for*superconductivity*. Used as the basis for a*charge qubit*, also known as a*superconducting charge qubit*,*superconducting transmon qubit*, or simply*transmon*. See the Wikipediaarticle.*Cooper pair***coordinate.**A*number*used in the specification of a location in a*space*. Alternatively, as a verb, to*synchronize*the*activities*of two or more*entities*.**coordinate system.**A*mathematical framework*for specifying a location in a*space*, using*coordinates*. See the Wikipediaarticle.*Coordinate system***coordination of quantum and classical parts of the computation.**In a*hybrid mode of operation*, the code at the*classical level*, executing on a*classical computer*, sends a*quantum circuit*to a*quantum computer*for*execution*. Upon completion of*quantum execution*, any*measured state*, referred to as*results*or*final results*is returned from the*quantum computer*to the*classical code*which is*executing*at the*classical level*for further*processing*. This*process*may be repeated as many times as needed (*iteration*) to complete the*execution*of the entire*computation*. Additional*software*running on the*quantum computer*and the*classical computer*facilitate the handoff of*control*and*data*between the two*computers*.**coplanar waveguide.**A*waveguide*for transmitting*microwaves*in a*quantum computer*to control, read, and enable*entanglement*of*qubits*. Abbreviated as*CPW*. See the Wikipediaarticle. See also:*Coplanar waveguide**resonator*.**coplanar waveguide (CPW) resonator.**See*coplanar waveguide*. See also:*resonator*.**coprocessor.**See*auxiliary processor*. Such as a classical floating-point coprocessor.**correction operation.**TBD.**correlated fermion systems.**TBD.**correlated fermionic systems.**TBD.**correlated fermions.**TBD.**correlated quantum simulations of chemistry.**TBD.**cost function landscape.**TBD.**coulomb.**The*unit*or*charge*or*current*. Approximately 6.242 times 10 to the 18th*electrons.*See the Wikipediaarticle.*Coulomb***Coulomb gate.**TBD.**couple.**See*coupling*,*couple qubits*, and*entangle*.**couple qubits.**To*entangle*(*couple*) the*quantum states*of two*qubits*. See also:*coupling resonator*.**coupled.**See*coupling*and*entangled*.**coupled qubits.**Two*qubits*whose*quantum states*are*entangled*(*coupled*.)**coupled transmon qubits.**TBD.**coupled two level system defect.**See*coupled two-level system defect*.**coupled two-level system defect.**TBD.**coupler.***Electronic device*used to*connect*or*couple*two or more*qubits*, such as to enable*quantum entanglement*. Commonly a*cavity*or*resonator*, or a*superconducting loop*. Referenced in thetutorial.*Introduction to the D-Wave Quantum Hardware***coupler flux bias.**TBD.**coupling.**See*entanglement*. They are synonyms. Two*qubits*can be*coupled*— their*quantum states*are then*entangled*.**coupling map.**See*connectivity map*. Which*qubits*may be*entangled*(*coupled*) and in what ways. Each*design*of*quantum computer*is different.**coupling resonator.**A*cavity*(*resonator*) used to*entangle*the*quantum state*of two*qubits*. See also:*readout resonator*. See thepaper by Majer, Chow, Gambetta, Koch, Johnson, Schreier, Frunzio, Schuster, Houck, Wallraff, Blais, Devoret, Girvin, and Schoelkopf.*Coupling Superconducting Qubits via a Cavity Bus***coupling strength.**TBD. Referenced indoc from Rigetti Computing.*The Quantum Processing Unit (QPU)***coupling strength between a qubit and a resonator.**TBD. Referenced indoc from Rigetti Computing.*The Quantum Processing Unit (QPU)***coupling strength between two neighboring qubits.**TBD. Referenced indoc from Rigetti Computing.*The Quantum Processing Unit (QPU)***CPHASE.**See*CPHASE gate*.**CPHASE gate.**See*controlled phase gate*. A*quantum logic gate*which applies a*phase*to a*qubit*if the*qubit*and a*control qubit*are both in the |1>*basis state*. [TBD: is it an absolute phase or a phase shift?] Synonym for*CPHASE11 gate*. Abbreviated as*CPHASE*. Referenced infrom Rigetti Computing. See also:*Source Code Documentation — pyquil.api**CPHASE00 gate*,*CPHASE01 gate*, and*CPHASE10 gate*.**CPHASE00.**See*CPHASE00 gate*.**CPHASE00 gate.**See*controlled phase gate*. A*quantum logic gate*which applies a*phase*to a*qubit*if the*qubit*and a*control qubit*are both in the |0>*basis state*. [TBD: is it an absolute phase or a phase shift?] Abbreviated as*CPHASE00*. Referenced infrom Rigetti Computing. See also:*Source Code Documentation — pyquil.api**CPHASE gate*,*CPHASE01 gate*,*CPHASE10 gate*, and*CPHASE10 gate*.**CPHASE01.**See*CPHASE01 gate*.**CPHASE01 gate.**See*controlled phase gate*. A*quantum logic gate*which applies a*phase*to a*qubit*if the*qubit*and a*control qubit*are in the |0> and |1>*basis states*respectively. [TBD: is it an absolute phase or a phase shift?] Abbreviated as*CPHASE01*. Referenced infrom Rigetti Computing. See also:*Source Code Documentation — pyquil.api**CPHASE gate*,*CPHASE00 gate*,*CPHASE10 gate*, and*CPHASE11 gate*.**CPHASE10.**See*CPHASE10 gate*.**CPHASE10 gate.**See*controlled phase gate*. A*quantum logic gate*which applies a*phase*to a*qubit*if the*qubit*and a*control qubit*are in the |1> and |0>*basis states*respectively. [TBD: is it an absolute phase or a phase shift?] Abbreviated as*CPHASE10*. Referenced infrom Rigetti Computing. See also:*Source Code Documentation — pyquil.api**CPHASE gate*,*CPHASE00 gate*,*CPHASE01 gate*, and*CPHASE11 gate*.**CPHASE11.**See*CPHASE11 gate*.**CPHASE11 gate.**See*controlled phase gate*. A*quantum logic gate*which applies a*phase*to a*qubit*if the*qubit*and a*control qubit*are both in the |1>*basis state*. [TBD: is it an absolute phase or a phase shift?] Synonym for*CPHASE gate*. Abbreviated as*CPHASE11*. Referenced infrom Rigetti Computing. See also:*Source Code Documentation — pyquil.api**CPHASE00 gate*,*CPHASE01 gate*, and*CPHASE10 gate*.**CPU.**Initialism for*central processing unit*.**CPW.**Initialism for*coplanar waveguide*.**crack.**To bypass a*security measure*, such as a*password*or*cryptographic key*.**crack a cryptographic key.**The use of one or more*high-performance computers*or a*quantum computer*to determine the*cryptographic key*for an*encrypted message*so that it can be*decrypted*. Technically, the goal is to get the*decryption key*, which allows an*encrypted message*to be read —*decrypted*. See*prime factorization problem*.**crack a decryption key.**See*crack a cryptographic key*.**crack an encryption key.**See*crack a cryptographic key*. Technically, the goal is to get the*decryption key*, which allows an*encrypted message*to be read —*decrypted*.**crack an encrypted message.**See*crack a cryptographic key*.**crest.**See*crest of a wave*. See also:*trough*and*zero crossing*.**crest of a wave.**The high point of a*wave*. The point with greatest*magnitude*in the positive direction. The opposite of the*trough of a wave*. See also:*zero crossing*.**cross entropy.**A measure of*logic gate errors*during the*execution*of a*quantum circuit*. See also:*circuit fidelity*. For detailed math, see thepaper.*Characterizing Quantum Supremacy in Near-Term Devices***cross entropy difference.**A measure used to compare the*execution*of an*algorithm*on a*quantum computer*with a comparable*algorithm*on a*classical computer*. See also:*cross entropy*.**cross-entropy benchmarking.**TBD. Abbreviated as*XEB*.**cross talk.**See*crosstalk*.**cross-talk.**See*crosstalk*.**crosstalk.**TBD.**crosstalk between neighboring resonant elements.**TBD. See thepaper by O’Brien, Vahidpour, Whyland, Angeles, Marshall, Scarabelli, Crossman, Yadav, Mohan, Bui, Rawat, Renzas, Vodrahalli, Bestwick, and Rigetti.*Superconducting Caps for Quantum Integrated Circuits***cryogenic.**See*cryogenics*.**cryogenics.**Relating to materials at extremely cold temperatures, cold enough that oxygen, nitrogen, and hydrogen gas liquefy. Or even colder, where helium liquefies. And even colder, where*superconductivity*occurs. Includes the techniques, processes, and equipment required to achieve, maintain, and operate at these ulta-cold temperatures, as well as the behavior of materials at these temperatures. Or even colder, close to absolute zero. Currently required for the operation of a*quantum computer*See the Wikipediaarticle. See also:*Cryogenics**cryostat*and*dilution refrigerator*.**cryogenic temperature.**Temperatures near*absolute zero*. Measured in degrees*kelvin*(*K*). 4 degrees*kelvin*, where helium gas liquefies, is considered warm by cryogenic standards.*Quantum computers*today commonly operate at 15 or 20*millikelvin*, 15 to 20-thousandths of a single degree*kelvin*, 0.015-degrees K to 0.020-degrees K, or 15*mK*to 20*mK*.**cryostat.**The*device*which achieves and maintains the intense, ultra-cold temperature required for*quantum computing*. See*cryogenics*. The equivalent of a car’s radiator and air conditioner for a*quantum computer*, the part that keeps the*qubit chips*super-cold, cooling them in the first place and dissipating heat as they operate. See the Wikipediaarticle. Synonym for*Cryostat**dilution refrigerator*. Technically, the latter is only part of the larger*cryostat*. Synonym for*refrigeration unit*— in the context of*quantum computing*.**cryptographic algorithm.**The*algorithm used for a*particular*cryptographic method*for*encryption*of*data*.**cryptographic key.**The*key*used to*encrypt*and*decrypt**cryptographic messages*. The product of two relatively large*prime numbers*. The two*prime numbers*then become the*encryption keys*for a message to be*encrypted*. Believed to be a very*hard problem*to solve — at least on a*classical computer*, while in theory a powerful*quantum computer*could solve the problem, although that has not happened, yet. See also:*post-quantum cryptography*. See the Wikipediaarticle. See also:*Key (cryptography)**prime factorization*and*RSA key*.**cryptographic message.**A*message*which has been*encrypted*using*cryptographic methods*.**cryptographic method**. An*approach*,*technique*,*algorithm*,*tool*, or*technology*used to produce and exchange*cryptographic keys*and*encrypt*and*decrypt**encrypted messages*. Alternatively, some particular combination of*cryptographic methods*.**cryptography.**The*methods*,*protocols*, and*technology*for encoding and decoding*messages*in a secure manner so that unauthorized parties may not decipher them. See the Wikipediaarticle. See also:*Cryptography**quantum cryptography*,*encryption*,*decryption*,*cryptographic methods*, and*post-quantum cryptography*.**crystal.**A*regular*three-dimensional arrangement of*atoms*,*ions*, or*molecules*. A*crystal lattice*. See the Wikipediaarticle. See also:*Crystal**crystalline*,*lattice*,*grid*.**crystal lattice.**Mathematical formalization of the structure of a*crystal*or*lattice*. See the Wikipediaarticle.*Bravais lattice***crystalline.**Having the structure of a*crystal*or*lattice*.**CSWAP.**See*CSWAP gate*.**CSWAP gate.**Controlled swap of the*states*of two*qubits*. Swap the*states*of two*qubits*if a third*qubit*is in the |1>*state*. See also:*SWAP gate*.**current.**See*electric current*. The flow of*electric charge*.**current general purpose quantum computer.**A*current quantum computer*which is fact a*general purpose quantum computer*, not a*fixed-purpose quantum computer*, and with sufficient power and capacity to handle a wide range of*real-world applications*.**current quantum computer.***Quantum computers*which are available today, in contrast to a*future quantum computer*, which may become available sometime in the future, possibly even far in the future, and*near-term quantum computer*, which is likely to be available in the near future or may currently be available. Also referred to as an*existing quantum computer*.**customer.**A business, organization, government agency, consumer, or consumer group or association which acquires (buys or leases)*products*and*services*from*vendors*. They may or may not be the true*user*or*end-user*, who may be staff, members, family members, or someone within another business, organization, government agency, consumer, or consumer group or association.**CV.**Initialism for*continuous variable*.**CV quantum computation.**See*continuous-variable quantum computation*.**CV quantum computing.**See*continuous-variable quantum computing*.**CV quantum information.**See*continuous-variable quantum information*.**CX.**See*CX gate*.**CX gate.**A*quantum logic gate*which performs a controlled rotation of a*qubit*about the X-axis by*pi*radians. The rotation is performed only if the specified*control qubit*is in the |1>*state*. Equivalent to the*CNOT gate*. Synonym for*controlled-X gate*. Abbreviated as*CX*. See also:*X gate*,*CY gate*, and*CZ gate*.**CY.**See*CY gate*.**CY gate.**A*quantum logic gate*which performs a controlled rotation of a*qubit*about the Y-axis by*pi*radians. The rotation is performed only if the specified*control qubit*is in the |1>*state*. Synonym for*controlled-Y gate*. Abbreviated as*CY*. See also:*Y gate*,*CX gate*, and*CZ gate*.**cybersecurity.**The technology, art, practice, and field of assuring that*computer systems*,*networks*, and*data*are not subject to unauthorized access, corruption, or disruption. Modern*cryptographic methods*are utilized to limit access to systems, networks, and data. Unfortunately,*traditional modern cryptographic methods*are potentially crackable using*quantum computers*, maybe not today, but eventually. See the NISTweb page.*Post-Quantum Cryptography***cycle.***Unit*of repetition, either of a single*event*or a sequence of related*events*. See also:*frequency*. Alternatively, a*process*which has a beginning, middle, and end.**cyclic multiplicative group.**TBD.**CZ.**See*CZ gate*.**CZ gate.**A*quantum logic gate*which performs a controlled rotation of a*qubit*about the Z-axis by*pi*radians. The rotation is performed only if the specified*control qubit*is in the |1>*state*. Synonym for*controlled-Z gate*. Abbreviated as*CZ*. See also:*Z gate*,*CX gate*, and*CY gate*.

To browse other parts of the glossary:

- Quantum Computing Glossary — Introduction.
- Quantum Computing Glossary — Part 1 — A-C. This part.
- Quantum Computing Glossary — Part 2 — D-G.
- Quantum Computing Glossary — Part 3 — H-P.
- Quantum Computing Glossary — Part 4 — Q.
- Quantum Computing Glossary — Part 5 — R-S.
- Quantum Computing Glossary — Part 6 — T-Z.