Quantum Computing Glossary — Part 6 — T-Z

30 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:

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 Wikipedia Tensor article. See also: 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 Wikipedia Tensor field article.
tensor product. Outer product of two vector spaces or matrices. See the Wikipedia Tensor product article. See also: Kronecker product. See Introduction to Quantum Computing doc from Rigetti 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 the Researchers achieve multifunctional solid-state quantum memory article. Shortened as 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 Microsoft The Q# Programming Language — Introduction web page.
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 the Low-cost quantum circuits for classically intractable instances of the Hamiltonian dynamics simulation problem paper by Nam and Maslov. See also: Heisenberg interaction.
time-dependent Schrödinger equation. TDB. See the Wikipedia Schrödinger equation article. Shortened as TDSE.
time-independent Schrödinger equation. TDB. See the Wikipedia Schrödinger equation article. Shortened as 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 Wikipedia Quantum logic gate and Toffoli gate articles.
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 Wikipedia Topological quantum computer article.
topological quantum error correcting code. TBD. See the Wikipedia Toric code article. See also: 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 Wikipedia Toric code article. See also: 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 Wikipedia Euler’s totient function article. Plural: 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 Wikipedia Public-key cryptography article. But even the 2048 and 4096 key sizes are not considered safe and secure in the post-quantum cryptography era, which is theoretically coming, but is not yet here. See the NIST Post-Quantum Cryptography web page. For a discussion of the vulnerabilities of even larger key sizes, see the Wikipedia Key size article.
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 the Open Quantum Assembly Language paper by Cross, Bishop, Smolin, and Gambetta.
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 Wikipedia Ion trap article. Also known as 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 Wikipedia Trapped ion quantum computer article. Also known as 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 Wikipedia Rydberg state article. See the Coherent control of a single trapped Rydberg ion paper.
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 Wikipedia Trigonometric functions article.
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 Wikipedia Multipartite entanglement article and the Bipartite entanglement in AJL’s algorithm for three-strand braids paper by Qu, Dong, Wang, Bao, Song, and Song. see also: bipartite entanglement and multipartite entanglement.
triplet spin qutrit. TBD. Referenced in the Universal holonomic quantum gates over geometric spin qubits with polarised microwaves paper by Nagata, Kuramitani, Sekiguchi, and Kosaka.
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 in The Quantum Processing Unit (QPU) doc from Rigetti Computing.
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 in The Quantum Processing Unit (QPU) doc from Rigetti Computing.
tunable transmons capacitively coupled to fixed-frequency transmons. See tunable transmon qubit capacitively coupled to fixed-frequency transmon qubit. Referenced in The Quantum Processing Unit (QPU) doc from Rigetti Computing.
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 the Elementary gates for quantum computation paper by Barenco, Bennett, Cleve, DiVincenzo, Margolus, Shor, Sleator, Smolin, and Weinfurter.
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 the Universal holonomic quantum gates over geometric spin qubits with polarised microwaves paper by Nagata, Kuramitani, Sekiguchi, and Kosaka.
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 the Universal holonomic quantum gates over geometric spin qubits with polarised microwaves paper by Nagata, Kuramitani, Sekiguchi, and Kosaka.
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 the Universal holonomic quantum gates over geometric spin qubits with polarised microwaves paper by Nagata, Kuramitani, Sekiguchi, and Kosaka.
two-qubit state tomography. TBD. Referenced in the Universal holonomic quantum gates over geometric spin qubits with polarised microwaves paper by Nagata, Kuramitani, Sekiguchi, and Kosaka.
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 the Open Quantum Assembly Language paper by Cross, Bishop, Smolin, and Gambetta of IBM. [TBD: Does “U” have a plain language meaning?].
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 the Open Quantum Assembly Language paper by Cross, Bishop, Smolin, and Gambetta of IBM.
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 the Open Quantum Assembly Language paper by Cross, Bishop, Smolin, and Gambetta of IBM.
u3. See u3 gate.
u3 gate. See U gate. Same parameters, same function. See also: u1 gate and u2 gate. See the Open Quantum Assembly Language paper by Cross, Bishop, Smolin, and Gambetta of IBM.
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 Wikipedia Ultraviolet article. Shortened as 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 the Circuit for Shor’s algorithm using 2n+3 qubits paper by Beauregard.
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 Wikipedia Uncertainty principle article.
uncomputation. TBD. See Wikipedia Uncomputation article.
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 Wikipedia Unicode article. See also: 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 Wikipedia Unit vector article. See also: 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 Wikipedia Unitarity (physics) article.
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 the Classical simulation complexity of extended Clifford circuits paper by Jozsa and Van den Nest.
unitary dynamics. TBD.
unitary evolution. TBD. Referenced in The Quantum Virtual Machine (QVM) doc from Rigetti Computing.
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 the Universal blind quantum computation paper by Broadbent, Fitzsimons, and Kashefi. See also: blind quantum computation.
universal gate set. See universal quantum logic gate set.
universal holonomic quantum gate. TBD. Referenced in the Universal holonomic quantum gates over geometric spin qubits with polarised microwaves paper by Nagata, Kuramitani, Sekiguchi, and Kosaka.
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 my What Is a Universal Quantum Computer? paper and the classic Quantum theory, the Church-Turing principle and the universal quantum computer paper by David Deutsch. Alternatively, in practice, the ability to compute the lion-share of 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 my What Is a Universal Quantum Computer? paper. See also: 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 Wikipedia Quantum logic gate article and the Universal Quantum Gates paper by Brylinski and Brylinski.
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 my What Is a Universal Quantum Computer? paper and the Wikipedia Quantum Turing machine article. See the Quantum Turing Machines Computations and Measurements paper by Guerrini, Martini, and Masini. See the classic Quantum theory, the Church-Turing principle and the universal quantum computer paper by David Deutsch. Shortened as QTM. See also: quantum Turing machine.
universal set of operations. See universal gate set.
universal variational quantum computation. TBD. See the Universal Variational Quantum Computation paper by Biamonte.
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 (data) 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 the Open Quantum Assembly Language paper.
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 the A Generalised Variational Quantum Eigensolver paper by Wang, Higgott, and Brierley. See also: 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 Wikipedia Vector space article. Synonym for 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 Wikipedia Voltage article.
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 Wikipedia W state article. See also: 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 the A fast quantum mechanical algorithm for database search paper by Grover.
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 Wikipedia Wave article. See also: 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 Wikipedia Wave function article.
wavelength. The distance electromagnetic radiation will travel to complete one cycle of its wave, crest to crest, trough to trough, or three zero-crossings since there is a zero-crossing in the middle of the wave. See the Wikipedia Wavelength article. See also: 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 in The Quantum Virtual Machine (QVM) doc from Rigetti Computing.
wavefunction simulation of unitary evolution. TBD. Referenced in The Quantum Virtual Machine (QVM) doc from Rigetti Computing.
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 Wikipedia Waveguide article. See also: 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 Wikipedia XML article. See also: XML data format.
XML data format. See extensible markup language (XML). See the Wikipedia XML article.
xmon qubit. TBD. Cross-shaped qubit. See the Coherent Josephson qubit suitable for scalable quantum integrated circuits paper by Barends, Martinis, et al.
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.
Y2Q. The moment when public key encryption based on semiprime numbers is cracked by a quantum computer which can rapidly factor a semiprime public key into its two component prime integers, such as with Shor’s factoring algorithm. Analogous to Y2K — a negative technical milestone by which time mitigation measures must be taken to avert a technological disaster. The solution is to shift to post-quantum cryptography, an effort which is underway under the auspices of NIST.
Z. See Z gate.
z-basis measurement. TBD.
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 Wikipedia Zero crossing article. See also: 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 the Universal holonomic quantum gates over geometric spin qubits with polarised microwaves paper by Nagata, Kuramitani, Sekiguchi, and Kosaka.
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 — Part 6 — T-Z

T-Z

Written by Jack Krupansky