# Quantum Computing Glossary — Part 6 — T-Z

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

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

# T-Z

**T.**See*T gate*.**T gate.**A*quantum logic gate*which rotates a*qubit*about the Z-axis by a fixed angle of*pi*divided by four*radians*(45 degrees.) Abbreviated as*T*. Equivalent to the*RZ gate*with an angle of*pi*divided by four. [TBD: what does T stand for?].**T1.**Symbol for*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*. See also:*T2*(*dephasing time*).**T2.**Symbol for*dephasing time*— how long a*qubit*can remain in a*superimposed state*before decaying to a |0> or |1> state, as measured using the*Hahn echo experiment*, but sometimes may be a sloppy reference to*T2**which is*dephasing time*measured using the*Ramsey experiment*. See also:*T1*(*amplitude coherence time*) and*T2**.**T2*.**Symbol for*dephasing time*— how long a*qubit*can remain in a*superimposed state*before decaying to a |0> or |1> state, as measured using the*Ramsey experiment*, in contrast to*T2*, which is*dephasing time*measured using the*Hahn echo experiment*. See also:*T1*(*amplitude coherence time*) and*T2*.**table.**A two-dimensional*model*,*presentation*, or*data structure*which organizes*information*into*rows*of*columns*. See also:*tabular*,*matrix*,*grid*,*lattice*,*array.***tabular.**Relating to the two-dimensional*structure*of a*table*.**tactic.**An*approach*to a narrow, specific issue, in contrast to a*strategy*which is more general and broad. See also:*technique*.**target machine.**The*machine*on which a*quantum program*,*quantum logic circuit*, or*data*is intended to be*executed*, in contrast to the*machine*on which a*tool*or other*software*which is*processing*an*intermediate representation*of that*code*or*data*is*executing*. Alternatively, in contrast to a*quantum simulator*on which the*program*may currently be*executing*.**taxonomy of classes.**A hierarchy of*classes*, such that each*class*is a subset of a broader*class*, and each*class*may have any number of subsidiary or narrower*classes*. Commonly viewed as a*tree*, with a root and branches. See also:*hierarchy of classes*.**TDSE.**Initialism for*time-dependent Schrödinger equation*.**team.**A*group of individuals*focused on a specific*project*or*operation*who are a relatively small portion of a larger*organization*. Usually a relatively small*group*and tightly integrated.**technical.**Relating to*technology*,*science*,*engineering*, or*mathematics*— so-called*STEM*.**technical professional.**A*professional*with*technical*(*STEM*) education,*training*,*knowledge*, and*experience*.**technically feasible.**A*technology*,*solution*,*application*, or*system*which can be*realized*at the present time by a reasonably skilled team of*technical professionals*using currently available*technology*at some reasonable cost, in contrast to*technology*which is strictly*theoretical*or a*speculative*with no feasible or credible technical*implementation*in sight. Cost per se is not an issue, as long as it is credible and not truly sky-high. See also:*practical solution*,*practical project*, and*practical cost*.**technique.**See*method*, but generally more limited, narrow, and specific, in contrast to a broader*strategy*. See also:*tactic*. Alternatively, style used to perform a*process*.**technology.**Some combination of*hardware*and*software*which offers*capabilities*and*functions*. May have some utility for some*purpose*, but although*application software*and*products*have a clear*purpose*,*technology*itself may not necessarily have any*purpose*per se, even if it does have a*function*. Commonly requiring some degree of scientific and technical*knowledge*and engineering*expertise*. Alternatively, the*design*, plans, or even*conceptions*for producing such a combination of*hardware*and*software*, even if it has not yet occurred.**temporal.**The*quality*of being arranged in*time*, with notions of the past, the present, and the future, and position in*time*and durations or*intervals*of*time*. See also:*spatial*.**tensor.***Mathematical framework*used in*physics*for solving multi-dimensional*problems*of*physical systems*involving*vectors*. Useful in*quantum mechanics*. [TBD: more detail]. See the Wikipediaarticle. See also:*Tensor**tensor field*.**tensor field.***Mathematical framework*which assigns a*tensor*to each point in a region of the space of a*physical system*. [TBD: detail, relevance to QM and QC]. See the Wikipediaarticle.*Tensor field***tensor product.***Outer product*of two*vector spaces*or*matrices*. See the Wikipediaarticle. See also:*Tensor product**Kronecker product*. Seedoc from Rigetti Computing.*Introduction to Quantum Computing***tensor product factors.**TBD.**text.**See*character string*, but emphasizing the*word*or*word*-like structure of the text. Alternatively, emphasis on*natural language text*with actual*words*and*punctuation*rather than mere*word*-like*identifiers*or simply a raw*sequence of characters*. May include*proper names*,*keywords*,*numbers*, and*symbols*as well. Synonym for*textual value*.**text search.**Either the use of a*regular expression*to identify occurrences of a*pattern*, or searching for instances of*words*,*numbers*,*names*,*phrases*, and other*patterns*based on*words*, otherwise known as*keyword search*. See also:*search engine*.**textual.**Have the quality of*text*, in contrast to*numeric*,*symbolic*, or*graphical*.**textual expression.**A thought, intention, or*information*which is represented in some*language*as*text*with some*syntax*.**textual value.**See*text*.**theoretical.**Relating to or of the nature of*theory*. Alternatively, synonym for*speculative*. See also:*theorize*.**theoretical design.**A*design*for a*computer*,*device*,*system*, or*software*which has been*theorized*but not yet*realized*(constructed) in the*real world*.**theoretical problem.**A*problem*which is of*theoretical*interest to an organization or individual, in contrast to a*research problem*, an*experimental problem*, or a*practical problem*.**theorize.***Imagine*,*conceptualize*,*formulate*, and*contemplate*a*conceptual approach*to a*problem*or to explain a*phenomenon*, but not necessarily*realize*that*conceptual approach*. May or may not be sufficient for a full*theory*.**theory.**The ideas and*principles*which serve to explain some*phenomenon*. A good*theory*should fully explain the*phenomenon*, fully account for past*observations*, provide*predictions*for future*outcomes*, and suggest experiments which can either*validate*or*falsify*the*theory*. See also:*quantum theory*and*quantum computing theory*.**theory of quantum computing.**See*quantum computing theory*.**theta.**Refers the the angle of rotation of the*quantum state*of a*qubit*about the horizontal, X axis of the*Bloch sphere*, measured in radians or degrees. See also*phi*.**three-dimensional quantum state.**TBD. Referenced in thearticle. Shortened as*Researchers achieve multifunctional solid-state quantum memory**3D quantum state*.**three levels of computation.**See*three levels of quantum computation*.**three levels of quantum computation.**The use of a*hybrid mode of operation*, where only some of the*computation*is performed on a*quantum computer*, with the rest of the*computation*performed on a*classical computer*. The first level is*classical computation*which obtains and*prepares*the*input data*and any user options, and initiates the second level, which is actual*quantum computation*, finally post-processing the*final quantum results*and presenting them to the user, or storing them, or passing them on to additional*classical computing*processing. The third level is*classical computation*which retrieves intermediate*measured results*of the second level, performs some intermediate*classical computation*and then optionally proceeds to initiate one or more additional*quantum computations*at the second level. See the Microsoftweb page.*The Q# Programming Language — Introduction***three-qubit gate.**A*quantum logic gate*with operates on three*qubits*.**threshold theorem.**See*quantum threshold theorem*.**time.**TBD.**time-dependent Heisenberg interaction.**TBD. Referenced in thepaper by Nam and Maslov. See also:*Low-cost quantum circuits for classically intractable instances of the Hamiltonian dynamics simulation problem**Heisenberg interaction*.**time-dependent Schrödinger equation.**TDB. See the Wikipediaarticle. Shortened as*Schrödinger equation**TDSE*.**time-independent Schrödinger equation.**TDB. See the Wikipediaarticle. Shortened as*Schrödinger equation**TISE*.**time-invertible.**See*time-invertible evolution*.**time-invertible evolution.**The*quality*of a*system*, especially a*quantum system*, that, in theory, all actions can be played out in reverse. The essential*meaning*is that no*information*is lost at each stage of the*evolution*(transition from one*state*to the next*state*), so that the*information*available at any given point in time can be used to deduce the*information*at the immediately preceding*moment of time*, simply by reversing the actions that occurred during that small time interval.**TIQIP.**Initialism for*trapped-ion quantum information processor*.**TISE.**Initialism for*time-independent Schrödinger equation*.**TLS.**Initialism for*two-level system*.**TLS defect.**TBD.**Toffoli (CCNOT) gate.**Performs a controlled-controlled-NOT operation on three*qubits*. It complements the*quantum state*of the third*qubit*if and only if both of the first two*qubits*are in the |1>*state*. See the Wikipediaand*Quantum logic gate*articles.*Toffoli gate***token.**The smallest*unit*of a*grammar*for a*language*, such as a*word*,*number*,*special character*, or*punctuation*. Alternatively, any*symbol*which is used as a*marker*for some purpose, typically to grant permission or to*synchronize*some*operation*.**tool.***Hardware*or*software*which facilitates the use of more complex*hardware*or*software*. See also:*software tool*and*utility software*.**topological protection against decoherence.**TBD.**topological quantum computer.**A theoretical*quantum computer*based on*qubits*constructed of*quantum braids*of*anyons*. See the Wikipediaarticle.*Topological quantum computer***topological quantum error correcting code.**TBD. See the Wikipediaarticle. See also:*Toric code**toric code*,*surface code*.**topological qubit.**A*qubit*constructed of*quantum braids*of*anyons*, used to construct a*topological quantum computer*.**topological superconductivity.**TBD.**toric code.**A*quantum error correcting code*based on periodic boundary conditions, which happen to be in the shape of a torus, hence the name. See the Wikipediaarticle. See also:*Toric code**topological quantum error correcting code*.**totative.**One of the positive integers which are counted by*Euler’s totient function*— all positive integers less than a specified number which are relatively prime to that specified number — the greatest common divisor of each such integer and the specified number is 1 — there are no common factors shared between each integer and the specified number. See the Wikipediaarticle. Plural:*Euler’s totient function**totatives*.**totient function.**See*Euler’s totient function*.**toy applications.***Contrived applications*which are too simplistic or more suitable for*testing*,*prototyping*, and*demonstration*, in contrast to*real-world applications*.**trace.**See*trace of a matrix*. Alternatively, a log of*operations*which have been performed.**trace of a matrix.**The sum of the*entries*on the*main diagonal*of a*square matrix*.**trace-preserving quantum operation.**TBD.**traditional computer.**See*classical computer*.**traditional computing.**See*classical computing*.**traditional digital computer.**A*computer*of the style and*architecture*used before the advent of*quantum computing*. See:*classical computer*.**traditional modern cryptographic algorithm.**See*traditional modern cryptographic method*.**traditional modern cryptographic key.**See*traditional modern cryptographic method*.**traditional modern cryptographic method.**Generally,*public-key cryptographic methods*are the gold standard for*cryptography*, safety, and*security*here in July 2018.*RSA key sizes*of 1024, 2048, and 4094 are common, and considered safe and secure, although there is some concern over 1024. See the Wikipediaarticle. But even the 2048 and 4096 key sizes are not considered safe and secure in the*Public-key cryptography**post-quantum cryptography era*, which is theoretically coming, but is not yet here. See the NISTweb page. For a discussion of the vulnerabilities of even larger key sizes, see the Wikipedia*Post-Quantum Cryptography*article.*Key size***traditional modern cryptography.**See*traditional modern cryptographic method*.**traditional modern public-key.**See*traditional modern public key*.**traditional modern public key.**See*traditional modern cryptographic method*.**traditional modern public-key cryptographic algorithm.**See*traditional modern cryptographic algorithm*.**traditional modern public-key cryptographic method.**See*traditional modern cryptographic method*.**traditional modern public-key cryptography.**See*traditional modern cryptographic method*.**transfer function.**TBD.**transform and execute a quantum algorithm.**See*transform and execute a quantum program*. Technically, this is probably a misnomer since a*developer*must come up with a*design*and mentally*transform*the*quantum algorithm*by hand into a*quantum program*based on that*design*first. Loosely, a lot of people confuse*algorithm*with*code*, treating them as exact synonyms.**transform and execute a quantum program.**All of the*processing steps*needed to take a*quantum algorithm*and carry it through*execution*, capturing of*final results*, and*post-processing*of those*final results*. See Figure 1 of thepaper by Cross, Bishop, Smolin, and Gambetta.*Open Quantum Assembly Language***transformation.**The*process*of*evolving*the*state*of something to a new*state*. For a*quantum system*this means applying an*operator*. For a*quantum computer*this means*executing*a*quantum logic operation*(*gate*). Alternatively, changing*information*from one format to another, such as*compilation of a program*or*post-processing of final results*.**transformation matrix.**The*mathematical matrix*used to express the precise*transformation*of a*quantum system*or*qubit*for a particular*operation*.**transition frequency.**See*qubit transition frequency*.**transmon.**See*superconducting transmon qubit*.**transmon qubit.**See*superconducting transmon qubit*.**transpose.**See*transpose a matrix*.**transpose a matrix.**Create a new*matrix*in which the*columns*of the original*matrix*become the*rows*of the new*matrix*.*Transposing*the new*matrix*will result in the original*matrix*.**transpose of a matrix.**See*transpose a matrix*.**transposed matrix.**See*transpose a matrix*.**transposing a matrix.**See*transpose a matrix*.**transverse coherence time.**TBD.**trapped-atom system.**See*trapped-ion computer*. [TBD: any nuances?].**trapped ion.**Any*method*of capturing and containing a*charged particle*(*ion*) using*electrical or magnetic fields*. Can be used to construct a*qubit*for a*quantum computer*. See Wikipediaarticle. Also known as*Ion trap**ion trap*.**trapped-ion architecture.**TBD.**trapped-ion quantum computer.**Any*quantum computer*whose*qubits*are based on*trapped ions*. See*trapped Rydberg ion quantum computer*. See the Wikipediaarticle. Also known as*Trapped ion quantum computer**ion trap quantum computer*.**trapped-ion quantum computing.***Computing*using a*trapped-ion quantum computer*.**trapped-ion quantum computer system.**A*computer system*based on a*trapped-ion quantum computer*.**trapped-ion quantum control.**TBD. The ability to manipulate the*quantum state*of a*trapped ion*, typically using*laser pulses*.**trapped-ion quantum information processor.**See*trapped-ion quantum computer*. Abbreviated as*TIQIP*.**trapped-ion qubit.**A*qubit*based on a*trapped ion*. See*trapped Rydberg ion qubit*.**trapped-ion system.**See*trapped-ion quantum computer*.**trapped Rydberg ion.***Trapped ions*which are excited to*Rydberg states*. See the Wikipediaarticle. See the*Rydberg state*paper.*Coherent control of a single trapped Rydberg ion***trapped Rydberg ion qubit.***Qubit*which is based on a*trapped Rydberg ion*.**trapped Rydberg ion quantum computer.**A*quantum computer*based on use of*trapped Rydberg ion qubits*.**trapped Rydberg qubit.**See*trapped Rydberg ion qubit*.**tree.**A hierarchical arrangement of*objects*or other*entities*into a*graph*with*nodes*, with a*root*or*root node*,*branches*or*branch nodes*, and*leaves*or*leaf nodes.*See also:*graph*,*structure*,*list*,*grid*,*table*, and*matrix*.**trigonometric function.**One of the standard, traditional trigonometric functions of*mathematics*— sine, cosine, tangent, cotangent, arcsine, arccosine, arctangent, etc. Arguments are*real values*and result is a*real value*, although they may be extended to cover*complex numbers*. See also:*standard mathematical functions*. See the Wikipediaarticle.*Trigonometric functions***tripartite entanglement.***Quantum entanglement*of exactly three*qubits*, in contrast to*bipartite entanglement*which is limited to only a*pair of qubits*. Alternatively, the*quality*of a*quantum computer*of supporting*entanglement*of three*qubits*in a particular*entanglement*at a time. Alternatively, the*quality*of a*quantum computer*of supporting*entanglement*of at least three*qubits*and possibly more than three*qubits*in a single*entanglement*. At present, here in August 2018,*current quantum computers*support only*bipartite entanglement*, no more than*pairs of qubits*. See the Wikipediaarticle and the*Multipartite entanglement*paper by Qu, Dong, Wang, Bao, Song, and Song. see also:*Bipartite entanglement in AJL’s algorithm for three-strand braids**bipartite entanglement*and*multipartite entanglement*.**triplet spin qutrit.**TBD. Referenced in thepaper by Nagata, Kuramitani, Sekiguchi, and Kosaka.*Universal holonomic quantum gates over geometric spin qubits with polarised microwaves***trivial circuit.**A*quantum logic circuit*with only a very few*quantum logic gates*. See also:*nontrivial circuit*.**Trotterization.**TBD.**trough.**See*trough of a wave*. See also:*crest*and*zero crossing*.**trough of a wave.**The low point of a*wave*. The point with greatest*magnitude*in the negative direction. The opposite of the*crest of a wave*. See also:*zero crossing*.**tunable coupler.**TBD.**tunable frequency.**A*frequency*which can vary and be*tuned*, such as for a*photon*or*microwave pulse*, in contrast to a*fixed frequency*, which cannot vary. See also:*resonator*,*resonant frequency*, and*frequency-tunable qubit*.**tunable qubit.**See*frequency-tunable qubit*. See also:*fixed-frequency qubit*.**tunable transmon.**See*tunable transmon qubit*.**tunable transmon qubit.**A*transmon qubit*whose*frequency*can be*tuned*, in contrast to a*fixed-frequency transmon qubit*.**tunable transmon capacitively coupled to fixed-frequency transmon.**See*tunable transmon qubit capacitively coupled to fixed-frequency transmon qubit*. Referenced indoc from Rigetti Computing.*The Quantum Processing Unit (QPU)***tunable transmon qubit capacitively coupled to fixed-frequency transmon qubit.**See*quantum entanglement*(*quantum coupling*). The use of*capacitive coupling*to achieve*quantum entanglement*of the*quantum states*of two*qubits*, one a*tunable transmon qubit*and the other a*fixed-frequency transmon qubit*. Referenced indoc from Rigetti Computing.*The Quantum Processing Unit (QPU)***tunable transmons capacitively coupled to fixed-frequency transmons.**See*tunable transmon qubit capacitively coupled to fixed-frequency transmon qubit*. Referenced indoc from Rigetti Computing.*The Quantum Processing Unit (QPU)***tune.**To vary or change the*frequency*, such as for a*device*.**tunnel.**A*method*of traveling or transiting through some barrier. See*tunneling of electrons*.**tunneling of electrons.**The effect of*quantum mechanics*which enables*electrons*to*tunnel*through an*insulator*, under controlled conditions. See*quantum tunneling*.**two-bit exclusive-OR gate.**Old name for the*CNOT gate*(*controlled-NOT gate*,*controlled-X gate*, or*CX gate*), vintage 1995. See thepaper by Barenco, Bennett, Cleve, DiVincenzo, Margolus, Shor, Sleator, Smolin, and Weinfurter.*Elementary gates for quantum computation***two level system.**See*two-level system*.**two level system defect.**See*two-level system defect*.**two-level system.**A*quantum system*which has exactly two discrete*quantum states*, corresponding to |0> and |1>, as well as*superposition*or a*linear combination*of both states simultaneously. This is a requirement for a*qubit*. Abbreviated as*TLS*.**two-level system defect.**TBD.**two-particle reduced density matrix.**TBD. Abbreviated as*2-RDM*.**two-qubit exclusive-OR gate.**See*two-bit exclusive-OR gate*.**two-qubit gate.**See*two-qubit logic gate*.**two-qubit gate fidelity.**TBD. Referenced in thepaper by Nagata, Kuramitani, Sekiguchi, and Kosaka.*Universal holonomic quantum gates over geometric spin qubits with polarised microwaves***two-qubit gate performance.**See*2-qubit gate performance*.**two-qubit holonomic gate.**Short for*two-qubit holonomic quantum logic gate*.**two-qubit holonomic logic gate.**Short for*two-qubit holonomic quantum logic gate*.**two-qubit holonomic quantum gate.**Short for*two-qubit holonomic quantum logic gate*.**two-qubit holonomic quantum logic gate.**TBD. Referenced in thepaper by Nagata, Kuramitani, Sekiguchi, and Kosaka.*Universal holonomic quantum gates over geometric spin qubits with polarised microwaves***two-qubit interaction.**See*quantum entanglement*or*quantum coupling*, where a change in the*quantum state*of one*qubit*will implicitly change the*quantum state*of another*qubit*to which it is*coupled*(*entangled*.) In contrast to*single-qubit control*, where the*quantum state*of a*qubit*is directly changed explicitly, such as with a*quantum logic gate*. See also:*two-qubit operation*and*two-qubit logic gate*.**two-qubit logic gate.**See*two-qubit quantum logic gate*.**two-qubit operation.**An*operation or quantum logic gate*which references two*qubits*, in contrast to a*single-qubit operation*which references only one*qubit*. Synonym for*two-qubit quantum logic gate*.**two-qubit quantum logic gate.**A*quantum logic gate*which operates on two*qubits*. Synonym for*two-qubit operation*. Abbreviated as*2Q gate*or*2Q*.**two-qubit quantum state tomography.**TBD. See*two-qubit quantum state tomography method*.**two-qubit quantum state tomography method.**TBD. Referenced in thepaper by Nagata, Kuramitani, Sekiguchi, and Kosaka.*Universal holonomic quantum gates over geometric spin qubits with polarised microwaves***two-qubit state tomography.**TBD. Referenced in thepaper by Nagata, Kuramitani, Sekiguchi, and Kosaka.*Universal holonomic quantum gates over geometric spin qubits with polarised microwaves***two-qubit states.**The four possible*quantum states*of two*qubits*, |00>, |01>, |10> and |11>, either individually or*superimposed*.**two-qubit unitary evolution.**TBD.**type.**A classification of*entities*such that*entities*of the same*type*have some fraction of their*qualities*or*properties*in common, and*entities*of different*types*less so. See*class*.**U.**see*U gate*.**U gate.**A*quantum logic gate*which is equivalent to three rotations of a*qubit*. It has three parameters, theta, phi, and lambda, each an angle in*radians*. Equivalent to*RZ*(phi),*RY*(theta), and*RZ*(lambda), in that order. See also:*u1 gate*,*u2 gate*, and*u3 gate*. See thepaper by Cross, Bishop, Smolin, and Gambetta of IBM. [TBD: Does “U” have a plain language meaning?].*Open Quantum Assembly Language***u1.**See*u1 gate*.**u1 gate.**A*quantum logic gate*which is equivalent to a single rotation of a*qubit*. It has a single parameter, lambda, an angle in*radians*. Equivalent to the*U gate*with parameter values of 0.0 for theta and phi. Equivalent to*RZ*(lambda). See also:*u2 gate*and*u3 gate*. See thepaper by Cross, Bishop, Smolin, and Gambetta of IBM.*Open Quantum Assembly Language***u2.**See*u2 gate*.**u2 gate.**A*quantum logic gate*which is equivalent to three rotations of a*qubit*, but it has only two parameters, phi and lambda, both angles in*radians*. Equivalent to the*U gate*with a parameter value of 0.0 for theta. Equivalent to*RZ*(phi),*RY*(*pi*/ 2), and*RZ*(lambda), in that order. See also:*u1 gate*and*u3 gate*. See thepaper by Cross, Bishop, Smolin, and Gambetta of IBM.*Open Quantum Assembly Language***u3.**See*u3 gate*.**u3 gate.**See*U gate*. Same parameters, same function. See also:*u1 gate*and*u2 gate*. See thepaper by Cross, Bishop, Smolin, and Gambetta of IBM.*Open Quantum Assembly Language***ubiquitous algorithmic primitive.**See*algorithmic building block*.**ultra-high-speed cryogenic SFQ computer.**See*single-flux-quantum computer*. By definition it will operate at*cryogenic temperatures*, and be very fast.**ultra-high-speed cryogenic SFQ computing.***Quantum computing*using a*single-flux-quantum computer*.**ultraviolet.**See*ultraviolet radiation*.**ultraviolet radiation.***Electromagnetic radiation*which is just above the threshold for visible violet*light*, with a slightly higher*frequency*and slightly shorter*wavelength*. People cannot directly see or feel*ultraviolet radiation*. See the Wikipediaarticle. Shortened as*Ultraviolet**ultraviolet*. Abbreviated as*UV*. See also:*infrared radiation*.**unauthorized access.**A*user*or*group of users*is attempting to gain*access*to a*resource*to which they have not been granted*authorization*. Alternatively, an explicit declaration of specific*users*or specific*groups of users*who are not permitted*access*to a particular*resource*. See also:*authorization*,*unrestricted access*, and*authorized access*.**unbounded Toffoli gates.**TBD. Referenced in thepaper by Beauregard.*Circuit for Shor’s algorithm using 2n+3 qubits***uncertainty.**The*quality*that an*outcome*is not assured or that a*result*is not guaranteed to be as expected, in contrast with*certainty*. 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:*nondeterministic*.**uncertainty principle.**See*Heisenberg’s uncertainty principle*. See the Wikipediaarticle.*Uncertainty principle***uncomputation.**TBD. See Wikipediaarticle.*Uncomputation***uncomputing.**See*uncomputation*.**undirected edge.**In*graph theory*, an*edge*which does not have a*direction*. See also:*undirected graph*.**undirected graph.**In*graph theory*, a*graph*whose*edges*are*undirected edges*. See also:*network*.**Unicode.**An approach to representing*characters*which do not fit in a traditional*8-bit byte*. See the Wikipediaarticle. See also:*Unicode**multi-byte character codes*.**Unicode Transformation Format.***Unicode*method of representing*character codes*which do not fit in a single*byte*. Abbreviated as*UTF*. See*multi-byte character codes*and*code units*.**uniform superposition.**TBD.**unit.**The smallest and indivisible measure of*quantity*. Alternatively, some number of*items*which are physically, logically, or functionally related to the extent that it makes sense to treat them together, as a*unit*. Alternatively, a synonym for*subsystem*, a collection of*components*which work together to form an integrated*unit*.**unit vector.***Vector*with a*magnitude*(length, or*absolute value*, or*modulus*) of 1.0. See the Wikipediaarticle. See also:*Unit vector**Bloch sphere*and*orthonormal*.**unitarity.**The principle of*quantum mechanics*that the sum of the*probabilities*of all possible states of a*quantum system*is 1.0*.*See the Wikipediaarticle.*Unitarity (physics)***unitary.**The concept that all*transformations*in a*quantum system*or*quantum computer*must be*reversible*. Mathematically, this means that multiplying the*transformation matrices*of an operation and its reverse must yield the*identity matrix*. Alternatively, an*operation*to be performed on the*quantum state*of a*qubit*, as defined by a*unitary matrix*— essentially a*quantum logic gate*.**unitary basis change.**TBD.**unitary Clifford circuit.**A*Clifford circuit*(*Clifford operation*) comprised of only*basic Clifford gates*—*H gate*,*T gate*, and*CZ gate*. A*Clifford circuit*in general may contain other types of*gates*, provided that their effect on the*quantum state*of*qubits*can be achieved using solely the*basic Clifford gates*. Referenced in thepaper by Jozsa and Van den Nest.*Classical simulation complexity of extended Clifford circuits***unitary dynamics.**TBD.**unitary evolution.**TBD. Referenced indoc from Rigetti Computing.*The Quantum Virtual Machine (QVM)***unitary matrix.**TBD.**unitary operator.**TBD.**unitary rotation.**A*quantum logic gate*which rotates the*quantum state*of a*qubit*around one of the three axes — x, y, or z.**unitary tomography.**TBD.**unitary tomography protocol.**TBD.**unitary transformation.**A*transformation*in a*quantum system*or performed by a*quantum logic gate*must be*reversible*. Mathematically, this means that multiplying the*transformation matrices*of an operation and its reverse must yield the*identity matrix*.**universal blind quantum computing.**TBD. See thepaper by Broadbent, Fitzsimons, and Kashefi. See also:*Universal blind quantum computation**blind quantum computation*.**universal gate set.**See*universal quantum logic gate set*.**universal holonomic quantum gate.**TBD. Referenced in thepaper by Nagata, Kuramitani, Sekiguchi, and Kosaka.*Universal holonomic quantum gates over geometric spin qubits with polarised microwaves***universal logic gate set.**See*universal quantum logic gate set*.**universal quantum computation.**Subject to practical*capacity*limitations, the ability of a*quantum computer*to do anything a*classical computer*can do, in addition to anything any*quantum computer*can do beyond the capabilities of a*classical computer*, in particular, supporting a*universal quantum logic gate set*. It must be able to compute all mathematically computable*functions*as well as able to simulate any*real physical quantum system*, subject to practical*capacity*limits. By definition, this includes all*classical computation*, including any*function*which is*computable*by a*classical Turing machine*. In theory,*universal quantum computation*is any*computation*possible by a*universal quantum Turing machine*. Even if a*quantum computer*is universal, it may not be able to practically do everything which a*classical computer*can do — it may have too few*qubits*, too short a*coherence*, or lack sufficient*quantum error correction*. See mypaper and the classic*What Is a Universal Quantum Computer?*paper by David Deutsch. Alternatively, in practice, the ability to compute the lion-share of*Quantum theory, the Church-Turing principle and the universal quantum computer**computations*which have*practical application*in the*real world*. Alternatively, the*computations*possible using a*universal quantum logic gate set*, in contrast to the limited set of functions supported by a special-purpose or*fixed-function quantum computer*, and in contrast to the full*functions*of a*classical Turing machine*. See also:*universal quantum computer*and*universal quantum logic gate set*.**universal quantum computer.**A*quantum computer*capable of*universal quantum computation*. A*quantum computer*which can be applied to all classes of*problems*and capable of*computing*whatever a*classical computer*can*compute*, in addition to anything a*quantum computer*can*compute*, including*simulation*of*real physical quantum systems*, in contrast to a*fixed-function quantum computer*which is tailored to only one relatively narrow niche class of*problems*. Note that universal refers to each of the discrete*operations*which can be performed, not necessarily the amount of*data*which can be processed or its*structure*. Alternatively, a*quantum computer*which supports a*universal quantum logic gate set*, in contrast to a special-purpose or*fixed-function quantum computer*, and in contrast to a*computer*supporting the full*functions*of a*classical Turing machine*. Alternatively, a vague marketing term asserting that a*quantum computer*or some purported*future quantum computer*is somehow all-powerful, or at least much more impressive than current and envisioned*classical computers*. Alternatively, again as a vague marketing term, simply a crude synonym for a*general purpose quantum computer*, in contrast to a*fixed-function quantum computer*. See mypaper. See also:*What Is a Universal Quantum Computer?**general purpose quantum computer*. Note that a*universal quantum computer*may not have the*resources*and*capabilities*to make it suitable as a*general purpose computer*.**universal quantum computing.**TBD. May be synonym for*general-purpose quantum computing*. See also:*universal quantum computer*.**universal quantum computing system.**See*universal quantum computer*.**universal quantum gates.**See*universal quantum logic gate set*.**universal quantum logic gate set.**A set of*quantum logic gates*or*operations*to which all possible sequences of theoretical*operations*possible on a*quantum computer*can be reduced. This set of*gates*needs to be sufficient to create all possible*quantum programs*. This does not necessarily imply that such a*quantum computer*is indeed a*universal quantum computer*. See the Wikipediaarticle and the*Quantum logic gate*paper by Brylinski and Brylinski.*Universal Quantum Gates***universal quantum Turing machine.**A hypothetical equivalent of the concept of a*universal Turing machine*of*classical computing*applied to*quantum computing*. This is the ultimate, ideal conception of a*universal quantum computer*, in*theory*even if not in practice. Such a conception has been neither formalized in*theory*nor*realized*in the lab in any*current quantum computer*or*near-term quantum computer*as of July 2018. See mypaper and the Wikipedia*What Is a Universal Quantum Computer?*article. See the*Quantum Turing machine*paper by Guerrini, Martini, and Masini. See the classic*Quantum Turing Machines Computations and Measurements*paper by David Deutsch. Shortened as*Quantum theory, the Church-Turing principle and the universal quantum computer**QTM*. See also:*quantum Turing machine*.**universal set of operations.**See*universal gate set*.**universal variational quantum computation.**TBD. See thepaper by Biamonte.*Universal Variational Quantum Computation***unrestricted access.**All*users*and all*groups of users*are permitted*access*to some*resource*without any need for explicit*authorization*, in contrast to*authorized access*and*unauthorized access*. See also:*authorization*.**unstructured information.***Information*(d*ata*) which has very little if any*structure*, including*raw data*,*raw text*, and*log files*. See also:*structured information*,*semi-structured information*,*knowledge*, and*insight*. Alternatively, simply a synonym for*data*.**up to a global phase.**TBD. See also:*up to a global phase factor*.**up to a global phase factor.**TBD. See also:*global phase factor*.**usable quantum computer.**TBD.**usable quantum device.**TBD.**usable qubit.**A potential technology for a*qubit*actually works in the lab and in practice, enabling working*qubits*to be*fabricated*and used in a*real quantum computer*, in contrast to an idea or*concept*for a*qubit*which has not yet been*realized*.**use.**To interact with a*system*for some*purpose*to achieve some*effect*, nominally to*solve*some*problem*or to*exploit*some*opportunity*. See also:*user*. Alternatively, the*purpose*for which a*system*is*used*.**useful quantum computation.**TBD.**user.**Any*entity*which interacts with any*system*. Any*entity*which*uses*a system. Most commonly, an*end-user*, a person who is not a*computer professional*or at least not a*software developer*, typically using*application software*. A*computer professional*or*software developer*is a*user*of a*computer*,*software tools*, and*programming languages*. Alternatively, a*user*may be*software*which invokes other*software*, essentially*automating*the actions of a real*user*.**user-defined gate.**A*quantum logic gate*(*operation*) which is defined by the*user*(*programmer*) in the QASM quantum assembly language. In contrast to a*built-in gate*. This requires manual defining the*entries of a matrix*to be used to implement the*logic gate*. See thepaper.*Open Quantum Assembly Language***UTF.**Initialism for*Unicode Transformation Format*. See*multi-byte character code*and*code unit*.**UTF-8.***UTF*which uses*8-bit code units*. See*multi-byte character code*.**UTF-16.***UTF*which uses*16-bit code units*. See*multi-byte character code*.**UTF-32.***UTF*which uses*32-bit code units*. See*multi-byte character code*.**utility.**The fact that something is useful. That is has*value*. Alternatively, see*utility software*.**utility software.**See*software tool*. Generally focused on facilitating the use of the specific*hardware*and*low-level software features*of a*computer system*, in contrast to facilitating the use of*applications*or*software development*..**UV.**Initialism for*ultraviolet*or*ultraviolet radiation*.**valid.**See*validate*. Desired status for a*theory*or a*value*.**valid coherence monotones.**TBD.**validate.**Confirm that a claim or*theory*is true —*valid*. See also:*falsify*.**validate a theory.**Propose and perform*experiments*which can confirm whether a*theory*is*valid*or can be*falsified*. Until*validated*, a*theory*is merely*speculative*.**validated quantum circuit.**A*quantum circuit*for which*quantum circuit validation*has been performed in advance of*execution*.**value.**A discrete*unit*of*data*. A*numeric value*or a*non-numeric*value. Alternatively, the*utility*of an*entity*to a*user*,*customer*, or*organization*. See also:*business value*.**variable.**A place where a*value*can be*stored*and retrieved (*accessed*), such as for use in an*algebraic expression*. The place will generally have a*symbolic name*.**variational 2-qubit gate.**TBD.**variational ansatz.**TBD.**variational fermionic simulation.**TBD.**variational parameter optimization.**TBD.**variational parameters.**TBD.**variational principle.**TBD.**variational quantum algorithm.**TBD.**variational quantum eigensolver.**See*variational quantum eigensolver algorithm*.**variational quantum eigensolver algorithm.***Method*for calculation of energy states for*real quantum systems*, such as for*computational chemistry*. Abbreviated as*VQE*. See thepaper by Wang, Higgott, and Brierley. See also:*A Generalised Variational Quantum Eigensolver**quantum phase estimation (QPE)*.**variational quantum eigensolver ansatz.**TBD. Abbreviated as*VQE ansatz*.**variational quantum simulator algorithm.**TBD.**variational quantum simulator technique.**TBD.**variational relaxation.**TBD.**vector.**Generally, an arrow which has a*magnitude*and a*direction*in some*coordinate system*. The units may be of any form of number, but most commonly*real numbers*or*complex numbers*, with*complex numbers*commonly used*quantum mechanics*and*quantum computers*. A*vector*is an element of a*vector space*. See also:*vector space*and*unit vector*.**vector space.**Oversimplifying since it is a very mathematical concept, the collection of all possible*vectors*in some*coordinate system*, including all possible additions and multiplications of all*vectors*in that*space*. May be finite or infinite. See also:*Hilbert space*, especially for*quantum computers*. Not needed for the average user of a*quantum computer*. See the Wikipediaarticle. Synonym for*Vector space**linear vector space*and*linear space*. See also:*basis*,*basis vector*,*basis state*,*quantum state*,*quantum system*.**velocity.**Rate of*motion*of an*object*or other*entity*in*space*. Includes both a*magnitude*(*speed*) and a*direction — velocity*is a*vector*. See also:*position*,*direction*, and*distance*.**vendor.**A*business*or*organization*which supplies*products*and*services*to*customers*, typically for some fee and for profit.**verification function.**TBD.**viable quantum computer.**A*design*for a*quantum computer*which is technically and economically feasible in a given timeframe — no additional research or laboratory experimentation is needed. Alternatively, includes the requirement that there be a nontrivial market or demand for the capabilities of that*machine*at the price at which it is marketed. There may be demand in very narrow, high-value niches, such as government research laboratories, defense or security applications, or*specialized applications*in large corporations, even if there is no general demand in a larger market for more modest sized corporations or for*general-purpose computing*. Also referred to as a*practical quantum computer*.**video.**Combination of visual imagery and*audio*, separate but*synchronized*. See also:*video signals*and*video processing*.**video camera.**A*device*for capturing*video*, including*audio*), either a*digital video camera*, or an old-fashioned video camera using magnetic tape.**video capture.**Recording of*video signals*, including associated*audio signals*. Could a*quantum computer*capture*video*and*audio*with much greater fidelity or at a much higher speed?**video processing.***Processing*of captured or live*video signals*. Includes*image processing*and*audio processing*, but*synchronized*and with special emphasis on*continuity*through imagery over time. 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:*audio processing*and*image processing*.**video signals.**The*waveforms*of*video*. Both the visual and the auditory, separate but synchronized.**virtual machine.**See*simulated computer*. Alternatively, a*software*which permits a*computer*to act as if a*computer program*had direct access to resources which it does not in fact have actual access to. Alternatively, an*interpreter*permitting direct*execution*of a*program*written in a*programming language*which is not translated into the*machine language*of the particular*computer*on which the*program*is being*executed*. The Java*programming language*and the Java*virtual machine*(JVM) is an example of the latter. Abbreviated as*VM*.**virtual memory.**A*hardware feature*which allows a*computer program*to*access memory*independently of how that*memory*is physically*organized*on the underlying*computer*. Abbreviated as*VM*.**visible light.**See*light*. Typically excludes*infrared*and*ultraviolet*.**visual.**The*quality*of visible and discernable appearance, generally associated with an*image*of the*real-world*, but can also be artificial or*imaginary*, such as*art*or a*computer-generated image*. See also:*graphical*and*spatial*.**VM.**Initialism for*virtual memory*or*virtual machine*.**voltage.**The*energy*of a*unit*of*current*or*charge*, the*unit*being one*coulomb*, which is proportional to a multiple of 6.242 times 10 to the 18th of the*energy*of a single*electron*. See the Wikipediaarticle.*Voltage***VQE.**Initialism for*variational quantum eigensolver*.**VQE ansatz.**Abbreviation for*variational quantum eigensolver ansatz*.**W state.**Three or more*qubits*which are*entangled*with only a single*qubit*in the |1>*state*and all remaining*qubits*in the |0>*state*. Most commonly, three*qubits*in the (|001> + |010> + |100>)/sqrt(3)*quantum state*. See the Wikipediaarticle. See also:*W state**GHZ state*and*multipartite entanglement*.**Walsh-Hadamard transform.**Perform a*Hadamard gate*on*n qubits*, which places the*qubits*into a*superposition*of 2^n discrete*quantum states*. Commonly used to prepare for*quantum parallelism*, to evaluate a*computation*on all 2^n*quantum states*simultaneously. Also referred to simply as a*Hadamard transform*.**Walsh-Hadamard transformation.**TBD. See*Walsh-Hadamard transform*. Referenced in thepaper by Grover.*A fast quantum mechanical algorithm for database search***wave.**The*movement*or*transmission*of*energy*through a*gas*,*plasma*,*liquid*, or*solid*, or*electromagnetic radiation*through a vacuum. Generally sinusoidal, with a frequency and*phase*, and possibly an*amplitude*. Includes*sound*or*mechanical waves*as well. Features a*crest*, a*trough*, and an intervening*zero crossing*. See the Wikipediaarticle. See also:*Wave**zero crossing of a wave*.**wave function.**In*quantum mechanics*, a mathematical formulation of the entire*quantum state*of a*quantum system*.*Superposition*permits multiple*wave functions*to be*composed*(*superimposed*) into a larger*wave function*. It is presumed that the*system*is essentially*isolated*from the*surrounding environment*. See the Wikipediaarticle.*Wave function***wavelength.**The distance*electromagnetic radiation*will travel to complete one*cycle*of its*wave*,*crest*to*crest*,*trough*to*trough*, or three*zero-crossing*s since there is a*zero-crossing*in the middle of the*wave*. See the Wikipediaarticle. See also:*Wavelength**frequency*.**waveform.**The*state*of a*wave*or collection of*waves*over a short or extended*period of time*.**waveform processing.**Analyzing the combined and individual*waves*in some localized region of*space*.*Computationally intensive*for a*classical computer*. Potential for acceleration by*quantum computing*, which could open up entire new avenues of pursuit. See also:*audio processing*and*video processing*.*Continuous processing*of*waves*may offer opportunities which*discrete processing*does not.**wavefunction simulation.**TBD. Referenced indoc from Rigetti Computing.*The Quantum Virtual Machine (QVM)***wavefunction simulation of unitary evolution.**TBD. Referenced indoc from Rigetti Computing.*The Quantum Virtual Machine (QVM)***waveguide.**A conduit for facilitating the transmission of*electromagnetic signals*between two*devices*. Commonly for*microwaves*, but*optical fiber*is also a*waveguide*. See the Wikipediaarticle. See also:*Waveguide**resonator*and*coplanar waveguide*.**weight.**The*constants*used in*linear combinations*to indicate the relative contributions of the various*vectors*being combined. These are*complex numbers*. The*vectors*are*eigenvectors*and the*constants*are their*eigenvalues*. In*quantum mechanics*, the*constants*will be the*amplitude*(*probability amplitude*) for each*basis state*(*basis vector*or*eigenvector*.) The*probability*that the*quantum system*is in a particular*basis state*(*basis vector*or*eigenvector*) is the square of the*modulus*of the*amplitude*(*probability amplitude*) — the sum of the squares of the*real part*and the*imaginary part*of the*complex number*representing the*amplitude*. See also:*eigenvalues and eigenvectors*.**well-motivated circuit ansatz.**TBD. In contrast to a*random number*.**whole number.**See*integer*. May actually be a*real number*which happens to not have any non-zero*fractional digits*.**wire.**A*conducting material*used to transmit*electrons*for*power*,*signals*, or*data*between*devices*. See also:*wired*.**wired.**When*devices*are*connected*with a*conducting medium*, such as copper*wiring*, in contrast to*wireless*or the use of a*waveguide*.**wireless.**See*wireless connection*. See also:*wireless communication*.**wireless communication.***Communication*which does not require a*physical connection*(*wiring*.) May be*radio waves*,*microwave*,*infrared*, or*visible light*.**wireless connection.**A*connection*between*devices*which are not*connected*physically with a wire, cable, or*optical fiber cable*or other*waveguide*.**wiring.**See*wire*. Loosely, may also include*fiber optic cable*, which conveys*data*but not*electrons*.**working prototype.**See*prototype*, with emphasis on the degree to which it is*fully functional*. There is no*requirement*that it be 100%*fully functional*, but simply offer enough*function*and*features*to prove its*value*.**X.**See*X gate*.**X gate.**See*Pauli-X gate*. A*quantum logic gate*which rotates a*qubit*about the X-axis by*pi*radians. Abbreviated as*X*. See also:*Y gate*and*Z gate*.**XEB.**Initialism for*cross-entropy benchmarking*.**XEB gate sequence.**TBD.**XML.**Initialism for*extensible markup language*. See the Wikipediaarticle. See also:*XML**XML data format*.**XML data format.**See*extensible markup language*(*XML*). See the Wikipediaarticle.*XML***xmon qubit.**TBD. Cross-shaped*qubit*. See thepaper by Barends, Martinis, et al.*Coherent Josephson qubit suitable for scalable quantum integrated circuits***Y.**See*Y gate*.**Y gate.**See*Pauli-Y gate*. A*quantum logic gate*which rotates a*qubit*about the Y-axis by*pi*radians. Abbreviated as*Y*. See also:*X gate*and*Z gate*.**Z.**See*Z gate*.**Z gate.**See*Pauli-Z gate*. A*quantum logic gate*which rotates a*qubit*about the Z-axis by*pi*radians. Abbreviated as*Z*. Synonym for*R-pi gate*. See also:*X gate*and*Y gate*.**zero crossing.**See*zero crossing of a wave*.**zero crossing of a wave.**The point in*space*or moment in*time*when the sign of the*value*of a*wave*is changing, going from negative to positive or from positive to negative. There are two*zero crossings*for each*cycle*of a*wave*when measured*crest*to*crest*or*trough*to*trough*, or three when measured*zero crossing*to*zero crossing*(one at each end and one in the middle of the*wave*.) See the Wikipediaarticle. See also:*Zero crossing**crest of a wave*and*trough of a wave*.**zero crossing of the wave.**See*zero crossing of a wave*.**zero-crossing.**See*zero crossing*.**zero-crossing of the wave.**See*zero crossing of a wave*.**zero-magnetic field.**TBD. Referenced in thepaper by Nagata, Kuramitani, Sekiguchi, and Kosaka.*Universal holonomic quantum gates over geometric spin qubits with polarised microwaves***zero state.**The*quantum state*of a*qubit*is |0>, equivalent to a*binary value*of 0, in contrast to the*one state*, which is equivalent to a*binary value*of 1. Note that a*qubit*can be in*both*the*zero state*and*one state*at the same time due to*superposition*.

To browse other parts of the glossary:

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