Quantum Computing Glossary — Part 1 — A-C

71 min readJul 20, 2018

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

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 in The Quantum Processing Unit (QPU) doc from Rigetti Computing. Synonym for 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 in The Quantum Processing Unit (QPU) doc from Rigetti Computing. Synonym for 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 the Team Demonstrates Multiple DOF, Solid-State Quantum Memory article.
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 Wikipedia Absolute value article.
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 Wikipedia Absolute zero article.
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 Wikipedia Access control article. Abbreviated as 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 the Classical simulation complexity of extended Clifford circuits paper by Jozsa and Van den Nest.
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 the Adiabatic Quantum Annealing Update presentation by Lucas. See also: adiabatic quantum computation.
adiabatic quantum computation. An algorithm to find the optimum for a function using the quantum adiabatic theorem. See the Wikipedia Adiabatic quantum computation article. See also 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 Wikipedia Alternating current article.
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 Wikipedia Amorphous solid article.
ampere. The unit for electric current. The flow of one coulomb of electric charge per second. See the Wikipedia Ampere article.
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 the Quantum Amplitude Amplification and Estimation paper by Brassard, Hoyer, Mosca, and Tapp. See also: amplitude 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 Wikipedia Analog computer article.
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 the Analog quantum computing (AQC) and the need for time-symmetric physics paper by Werbos and Dolmatova. See also: 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 Wikipedia Ancilla bit article.
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 Wikipedia Angular momentum article. See also: spin.
anharmonicity of a qubit. See anharmonicity of the qubit.
anharmonicity of the qubit. TBD. Referenced in The Quantum Processing Unit (QPU) doc from Rigetti Computing.
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 in Breaking Down the Quantum Swap blog post by Gidney.
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 Wikipedia Main diagonal article. See also: 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 Wikipedia Anyon and Topological quantum computer articles. See also 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 QEC. Initialism for approximate quantum error-correction.
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 Approximation Methods in QM. See also: 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 error correcting code. See approximate quantum error-correcting code.
approximate quantum error-correcting code. TBD. See the Complexity and order in approximate quantum error-correcting codes paper by Yi, Ye, Gottesman, and Liu. Abbreviated as AQEC code.
approximate quantum error correction. See approximate quantum error-correction.
approximate quantum error-correction. TBD. See approximate quantum error-correcting code. Abbreviated as AQEC. Also abbreviated as approximate QEC.
approximate quantum error-correction code. See approximate quantum error-correcting code.
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.
AQEC. Initialism for approximate quantum error-correction.
AQEC code. Initialism for approximate quantum error-correction code. Alternatively, initialism for approximate quantum error-correcting code.
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 Wikipedia Artificial intelligence article. Abbreviated as 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 Wikipedia Automata theory article. See also 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 in The Quantum Processing Unit (QPU) doc from Rigetti Computing.
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 the Scaling laws for Shor’s algorithm with a banded quantum Fourier transform paper by Nam and Blümel. Synonym for 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 the Open Quantum Assembly Language paper.
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 the Classical simulation complexity of extended Clifford circuits paper by Jozsa and Van den Nest. See also: 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 Wikipedia Basis (linear algebra) article.
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 MIT Quantum Theory of Radiation Interactions online course lecture notes.
BB84. A protocol for quantum encryption developed by Charles Bennett and Gilles Brassard in 1984. See the Wikipedia BB84 article.
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 Wikipedia Bell state article. Also referred to as a 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 Wikipedia Bell state article and 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 Wikipedia Bell’s theorem article.
Bernstein-Vazirani algorithm. TBD. Referenced in Riggetti Grove docs, UW-Madison CS 880 — Quantum Information Processing course lecture notes, and 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 Wikipedia Big O Notation article and the What Is Quantum Advantage and What Is Quantum Supremacy? paper. May also be written as 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 the Bipartite entanglement in AJL’s algorithm for three-strand braids paper by Qu, Dong, Wang, Bao, Song, and Song. see also: 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 the Universal blind quantum computation paper by Broadbent, Fitzsimons, and Kashefi. See also: 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 Wikipedia Bloch sphere article.
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 Wikipedia Boolean algebra article.
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 Wikipedia Boolean algebra article, but also see the documentation for the 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 Wikipedia Boolean algebra article, but also see the documentation for the 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 Wikipedia Bose–Einstein statistics article.
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 Wikipedia Boson article.
boson sampling. A theoretical approach to quantum computing using photons and the linear optical quantum computing paradigm. See the Wikipedia Boson sampling article.
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 Wikipedia Bound state article. See also: 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 Wikipedia BQP article. See also: 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 Wikipedia Bra–ket notation article. See also: 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 Wikipedia Brute-force search article. Synonym for 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 the Open Quantum Assembly Language paper.
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 Wikipedia Capacitor article.
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 Wikipedia Capacitor article. See also: 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 Wikipedia Cat state article.
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 the Coupling Superconducting Qubits via a Cavity Bus paper by Majer, Chow, Gambetta, Koch, Johnson, Schreier, Frunzio, Schuster, Houck, Wallraff, Blais, Devoret, Girvin, and Schoelkopf.
cavity QED. See cavity quantum electrodynamics.
cavity quantum electrodynamics. The use of light trapped in a cavity to implement a qubit. TBD. See the Wikipedia Cavity quantum electrodynamics article. Also referred to as 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 Wikipedia Cellular automaton article. See also: 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 Wikipedia Chaos theory article.
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 Wikipedia Transmon and Charge qubit articles. See also: 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 Wikipedia Chemical bond article.
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 Wikipedia Chemistry article.
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 the Solving Set Cover with Pairs Problem Using Quantum Annealing paper by Cao, Jiang, Perouli, and Kais and the Quantum walk on a chimera graph paper by Xu, Sun, Wu, Zhang, Arshed, and Sanders. See also: 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 the Universal holonomic quantum gates over geometric spin qubits with polarised microwaves paper by Nagata, Kuramitani, Sekiguchi, and Kosaka.
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 Wikipedia Bus (computing) article.
classical chaos theory. Chaos theory studies and models the behavior of dynamic systems, in a classical, rather than quantum sense. See the Wikipedia Chaos theory article. See also: 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 the A Practical Quantum Instruction Set Architecture paper by Smith, Curtis, and Zeng of Rigetti Computing.
classical/quantum algorithm. An algorithm based on the hybrid mode of operation. See the A Practical Quantum Instruction Set Architecture paper by Smith, Curtis, and Zeng of Rigetti Computing.
classical quantum chemistry. TBD.
classical/quantum computation. A computation based on the hybrid mode of operation. See the A Practical Quantum Instruction Set Architecture paper by Smith, Curtis, and Zeng of Rigetti Computing.
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 Wikipedia State (computer science) article. May or may not describe all of the fine detail of the 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 the Classical simulation complexity of extended Clifford circuits paper by Jozsa and Van den Nest. See also: adaptive Clifford circuit and non-adaptive Clifford circuit.
Clifford computation. TBD. Referenced in the Classical simulation complexity of extended Clifford circuits paper by Jozsa and Van den Nest.
Clifford computational task. TBD. Referenced in the Classical simulation complexity of extended Clifford circuits paper by Jozsa and Van den Nest.
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 the Classical simulation complexity of extended Clifford circuits paper by Jozsa and Van den Nest. See also: non-clifford gate.
Clifford group. TBD. See the Representations of the multi-qubit Clifford group paper by Helsen, Wallman, Wehner.
Clifford operation. See Clifford circuit. TBD. Referenced in the Classical simulation complexity of extended Clifford circuits paper by Jozsa and Van den Nest. See also: 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 Wikipedia Coaxial cable article.
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 in The Quantum Processing Unit (QPU) doc from Rigetti Computing. See also: 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 Wikipedia Coherent control article.
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 Wikipedia Row and column vectors article. See also 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 in National Quantum Initiative Act bill.
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 Wikipedia Complex number article. Abbreviated as 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 Wikipedia Computational chemistry article.
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 Wikipedia Computational complexity and Computational complexity theory articles and the What Is Quantum Advantage and What Is Quantum Supremacy? paper.
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 Wikipedia Computational complexity and Computational complexity theory articles.
computational diversity. The use of a variety of types of computing hardware — classical digital processors — both basic processors and high-end processors, multiple classical processors, supercomputers with a large number of processors, analog signal processing, GPUs, FPGAs, custom hardware, and finally, quantum computers.
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 the Embracing computational variety report from Accenture.
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 computation, including the computation itself. Efforts required to satisfy computing needs.
concentric transmon. See concentric transmon qubit.
concentric transmon qubit. TBD. See the Concentric transmon qubit featuring fast tunability and an anisotropic magnetic dipole moment paper by Braumüller, Sandberg, Vissers, Schneider, Schlör, Grünhaupt, Rotzinger, Marthaler, Lukashenko, Dieter, Ustinov, Weides, and Pappas.
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 the Polynomial-Time Algorithms for Prime Factorization and Discrete Logarithms on a Quantum Computer paper by Shor.
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 the 16-qubit IBM universal quantum computer can be fully entangled paper by Wang, Li, Yin, and Zeng.
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 the Preparing encoded states in an oscillator paper by Travaglione and Milburn.
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 Wikipedia Quantum walk article.
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 the Analog quantum computing (AQC) and the need for time-symmetric physics paper by Werbos and Dolmatova. See also: 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 the Continuous-Variable Quantum Computing in Optical Time-Frequency Modes using Quantum Memories paper by Humphreys, Kolthammer, Nunn, Barbieri, Datta, and Walmsley. Shortened as CV quantum computation. See also: continuous-variable quantum computing and continuous-value quantum information.
continuous-variable quantum computing. TBD. Referenced in the Continuous-Variable Quantum Computing in Optical Time-Frequency Modes using Quantum Memories paper by Humphreys, Kolthammer, Nunn, Barbieri, Datta, and Walmsley. Shortened as CV quantum computing. See also: continuous-value quantum computation and continuous-value quantum information.
continuous-variable quantum information. TBD. Referenced in the Continuous-Variable Quantum Computing in Optical Time-Frequency Modes using Quantum Memories paper by Humphreys, Kolthammer, Nunn, Barbieri, Datta, and Walmsley. Shortened as 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 the A Quantum Computer Foundation for the Standard Model and SuperString Theories paper. Unclear if this has any general acceptance.
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 in NSF launches effort to create first practical quantum computer news release.
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 Wikipedia Quantum logic gate article. See also: 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 the Circuit for Shor’s algorithm using 2n+3 qubits paper by Beauregard.
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 Wikipedia Quantum logic gate article.
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 in Source Code Documentation — pyquil.api from Rigetti Computing. See the Heralded quantum controlled phase gates with dissipative dynamics in macroscopically-distant resonators paper by Qin, Wang, Miranowicz, Zhong, and Nori. See also: 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 Wikipedia Cooper pair article.
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 Wikipedia Coordinate system article.
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 Wikipedia Coplanar waveguide article. See also: 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 Wikipedia Coulomb article.
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 the Introduction to the D-Wave Quantum Hardware tutorial.
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 the Coupling Superconducting Qubits via a Cavity Bus paper by Majer, Chow, Gambetta, Koch, Johnson, Schreier, Frunzio, Schuster, Houck, Wallraff, Blais, Devoret, Girvin, and Schoelkopf.
coupling strength. TBD. Referenced in The Quantum Processing Unit (QPU) doc from Rigetti Computing.
coupling strength between a qubit and a resonator. TBD. Referenced in The Quantum Processing Unit (QPU) doc from Rigetti Computing.
coupling strength between two neighboring qubits. TBD. Referenced in The Quantum Processing Unit (QPU) doc from Rigetti Computing.
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 in Source Code Documentation — pyquil.api from Rigetti Computing. See also: 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 in Source Code Documentation — pyquil.api from Rigetti Computing. See also: 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 in Source Code Documentation — pyquil.api from Rigetti Computing. See also: 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 in Source Code Documentation — pyquil.api from Rigetti Computing. See also: 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 in Source Code Documentation — pyquil.api from Rigetti Computing. See also: 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 the Characterizing Quantum Supremacy in Near-Term Devices paper.
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 the Superconducting Caps for Quantum Integrated Circuits paper by O’Brien, Vahidpour, Whyland, Angeles, Marshall, Scarabelli, Crossman, Yadav, Mohan, Bui, Rawat, Renzas, Vodrahalli, Bestwick, and Rigetti.
CRQC. Initialism for cryptanalytically relevant quantum computer.
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 Wikipedia Cryogenics article. See also: 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 Wikipedia Cryostat article. Synonym for dilution refrigerator. Technically, the latter is only part of the larger cryostat. Synonym for refrigeration unit — in the context of quantum computing.
cryptanalytically relevant quantum computer. A quantum computer with sufficient size and sophistication to enable it to crack public-key cryptography. Would need sufficient qubit count, qubit fidelity, qubit connectivity, coherence time, maximum circuit depth, and fine granularity of phase to execute Shor’s factoring algorithm or a similar factoring algorithm for public keys with lengths of 1024, 2048, or 4096 bits. As of this writing on May 4, 2022, no such quantum computer (no CRQC) is known to exist and none is expected to be introduced within the next few years. Abbreviated as CRQC.
cryptanalytically-relevant quantum computer. See cryptanalytically relevant quantum computer.
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 Wikipedia Key (cryptography) article. See also: 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 Wikipedia Cryptography article. See also: 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 Wikipedia Crystal article. See also: crystalline, lattice, grid.
crystal lattice. Mathematical formalization of the structure of a crystal or lattice. See the Wikipedia Bravais lattice article.
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 NIST Post-Quantum Cryptography web page.
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 — Part 1 — A-C

Glossary A-C

Written by Jack Krupansky

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