Quantum Computing Glossary — Part 4 — Q

61 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:

Q

QA. Initialism for quantum annealer, quantum annealing, and quantum annealing system.
QA&A. Initialism for quantum algorithms & applications or quantum algorithms and applications.
QAA. Initialism for quantum amplitude amplification.
QAC. Initialism for quantum adiabatic computing model.
QAE. Initialism for quantum autoencoder and quantum autoencoder algorithm.
QAHE. Initialism for quantum anomalous Hall effect.
QAM. Initialism for quantum abstract machine.
QAOA. Initialism for quantum approximate optimization algorithm. Alternatively, initialism for quantum alternating operator ansatz.
QAOA ansatz. TBD.
QASM. Initialism for quantum assembly language.
QBC. Initialism for quantum bit commitment.
qbit. See qubit and quantum bit. More proper to use qubit.
QC. Initialism for quantum computing, quantum computation, or quantum computer.
QCA. Initialism for quantum cellular automaton.
QCCD. Initialism for quantum charge-coupled device.
QD. Initialism for quantum dot.
QD quantum computing. See quantum dot quantum computer.
QDQC. Initialism for quantum dot quantum computer.
QEC. Initialism for quantum error correction.
QECC. Initialism for quantum error-correcting codes.
QEM. Initialism for quantum error mitigation.
QFA. Initialism for quantum finite-state automaton.
QFT. Initialism for quantum Fourier transform in the context of quantum computing or quantum field theory in the context of quantum mechanics.
QKD. Initialism for quantum key distribution.
QLA. Initialism for quantum-limited amplifier.
QMC. Initialism for quantum Monte Carlo.
QMI. Initialism for quantum machine instruction.
QML. Initialism for quantum machine learning.
QND. Initialism for quantum non-demolition or quantum non-demolition measurement.
QNN. Initialism for quantum neural network or quanvolutional neural network.
QOFA. Initialism for quantum-order finding algorithm.
QPE. Initialism for quantum phase estimation.
QPEA. Initialism for quantum phase estimation algorithm. Alternatively, QPE or PEA.
QPT. Initialism for quantum process tomography.
QPU. Initialism for quantum processing unit.
QPU element. Short for quantum processing unit element.
QST. Initialism for quantum state tomography.
qRAM. Initialism for quantum random access memory.
QRAM. See qRAM.
QTM. Initialism for quantum Turing machine.
quadratic complexity. An algorithm whose computational complexity is approximately the square of its input size — O(n²). Not to be confused with a quadratic speedup which is essentially the inverse of quadratic complexity — O(sqrt(n)).
quadratic speedup. An algorithm which exhibits a computational complexity of O(sqrt(n)) compared to an algorithm of linear complexity, O(n). An example is Grover’s algorithm. Not to be confused with quadratic complexity, O(n²) — a quadratic speedup is essentially the inverse of quadratic complexity. See the What Is Quantum Advantage and What Is Quantum Supremacy? paper.
quadratic unconstrained binary optimization problem. The type of optimization problem which is particularly well-suited for a quantum annealer, such as the D-Wave special-purpose quantum computer. Abbreviated as QUBO. See the Quadratic Unconstrained Binary Optimization Problem Preprocessing: Theory and Empirical Analysis paper by Mark Lewis and Fred Glover.
quality. An aspect of an entity which can be observed, measured, detected, or modeled, directly or indirectly. See also: characteristic, property, and attribute. Alternatively, the degree to which a product or service satisfies its users. Ranging from low quality to high quality. Largely subjective, but sometimes metrics can be defined and measured or calculated. Metrics could include bugs, performance, and response time. For a quantum computer, coherence would be a prime metric.
quanta. Smallest physically possible unit of some physical quantity. The smallest amount of a physical quantity which can be measured. The smallest measure of a physical quantity. For example, a photon of light or electromagnetic radiation.
quantify. Count or measure something.
quantity. Something that can be quantified. Alternatively, the count or measure of something. This term can be used either way, to refer to that which is being counted or measured, or alternatively to refer to the actual count or measurement. In quantum mechanics, there is a correspondence between an operator, an observable, and a quantity of the quantum system under study. In quantum computing, quantity can refer to the quantum state of a qubit, both as it exists as a superposition of quantum states and also as it would be measured as a real quantity in the form of a real number. See also: real quantity.
quantitative and operational connection. TBD.
quantum. General reference to quantum computing or to the principles of quantum mechanics. Alternatively, in context, a general reference to the concept of the smallest, individual, discrete, indivisible unit by which two phenomena, observations, or measurements can differ.
quantum abstract machine. A programming model for a quantum computer. The features which the developer may use and the rules which they must follow. Abbreviated as QAM. See the A Practical Quantum Instruction Set Architecture paper by Smith, Curtis, and Zeng of Rigetti Computing.
quantum acyclic circuit. TBD. Analogous to acyclic circuits in classical computer science.
quantum adiabatic computing model. TBD. Abbreviated as QAC.
quantum adiabatic theorem. If environmental conditions are evolving slowly enough, the quantum system can adapt accordingly, but if environmental conditions are evolving too rapidly, the system will not evolve significantly. See the Wikipedia Adiabatic theorem article.
quantum advantage. At least in the context of a particular application of interest, a quantum computer can perform a computation significantly faster than even the best classical computer or no classical computer may be able to perform the computation at all — or at least not in some reasonable amount of time or with a reasonable number of classical computers in a distributed or networked configuration. Note that a quantum advantage in one or more applications does not necessarily imply an overall quantum advantage in any other application or across all applications. The central essence of quantum advantage is quantum parallelism which enables quantum algorithms to execute with a computational complexity which is polynomial in contrast with classical algorithms which tend to have a greater (worse) computational complexity which is superpolynomial, such as exponential. Or in general, the computational complexity of an algorithm on a quantum computer grows significantly more slowly than for the best comparable algorithm on the best classical computer as the size of the input or complexity of the problem to be solved grows — Big-O for a quantum algorithm on a quantum computer is much smaller than Big-O for the best algorithm on a classical computer. May sometimes be used as a synonym for quantum supremacy, quantum preeminence, or quantum ascendency. May refer to a specific characterization of how much faster or better a quantum computer can execute a particular algorithm compared to a comparable algorithm on a classical computer — the specific advantage. See also: quantum speedup. May also refer to the eventual advantage and promise of quantum computers, as opposed to capabilities which are available today or likely will be in the fairly near-term future. [TBD: See more discussion in the (upcoming) What Is Quantum Advantage and What Is Quantum Supremacy? paper.]
quantum algorithm. An algorithm designed to be executed on a quantum computer. A quantum algorithm would be implemented by a quantum logic circuit or a quantum program. See also: famous quantum algorithms.
quantum algorithm design. The process of designing a quantum algorithm. Creating a quantum algorithm. Construction of a quantum algorithm. See also: quantum programming.
quantum algorithm designer. An individual, typically a professional, who designs quantum algorithms. See also: quantum programmer.
quantum algorithms & applications. See quantum algorithms and applications. Abbreviated as QA&A.
quantum algorithms and applications. Both quantum algorithms and quantum applications — applications which use quantum algorithms. Abbreviated as QA&A. Also written as quantum algorithms & applications.
quantum algorithms and software. Quantum algorithms, quantum logic circuits, and quantum programs, collectively. In addition, may include any complementary classical software for a hybrid mode of operation.
quantum alternating operator ansatz. A quantum algorithm for combinatorial optimization problems which extends the concept of a quantum approximate optimization algorithm by allowing alternation between more general families of operators with general parameterized families of unitaries rather than only those corresponding to the time evolution under a fixed local Hamiltonian for a time specified by the parameter. Abbreviated as QAOA, but may be confused with quantum approximate optimization algorithm, which has the same abbreviation. See the From the Quantum Approximate Optimization Algorithm to a Quantum Alternating Operator Ansatz paper by Hadfield, Wang, O’Gorman, Rieffel, Venturelli, and Biswas.
quantum amplifier. TBD.
quantum amplitude. See probability amplitude. The probability amplitude for a qubit being in a particular quantum basis state, |0> or |1>, a complex number, the square of whose modulus (absolute value) is the probability that the qubit is in that particular quantum basis state. Each quantum basis state has its own amplitude (probability amplitude.) When a qubit is in a quantum state which is a superposition of two quantum basis states, each has its own quantum amplitude and hence probability. The sum of those probabilities is, by definition, 1.0. For example, after execution of the Hadamard (H) gate, the probability of being in the |0> state is 0.5 and 0.5 for the |1> state as well, also meaning that the probability that measurement of the qubit would return 0 is 0.5 and 0.5 for 1 as well. The actual probability amplitude would be a complex number, the square of whose modulus would be 0.5. By definition, quantum amplitude itself is neither visible, observable, detectable, or measurable for a quantum system or a quantum computer — once a qubit is measured, the quantum amplitudes are lost as the quantum state (wave function) collapses to the particular value returned by the measurement.
quantum amplitude amplification. TBD. See the Wikipedia Amplitude amplification article. See the Quantum Amplitude Amplification and Estimation paper by Brassard, Hoyer, Mosca, and Tapp. See Grover’s Algorithm web page in IBM Q Experience documentation. See also: Grover’s algorithm, amplitude estimation, and oblivious amplitude amplification. Abbreviated as QAA. Commonly shortened as amplitude amplification.
quantum analog computer. Vague term, but sometimes applied to a quantum annealing processor or adiabatic quantum computing. Synonym for analog quantum computer.
quantum annealer. See quantum annealing computer.
quantum annealing. An algorithm for finding the global minimum for a function (an objective function.) [TBD: summarize utility]. See the Wikipedia Quantum annealing article. See also quantum annealing computer, simulated annealing, and reverse quantum annealing. Abbreviated as QA.
quantum annealing computer. A quantum computer which is programmed for quantum annealing (QA).
quantum annealing processor. See quantum annealing computer.
quantum annealing system. See quantum annealing computer.
quantum anomalous Hall effect. TBD. Potential for construction of qubits for a topological quantum computer. Shortened as QAHE. See the Wikipedia Quantum anomalous Hall effect article. See the The quantum anomalous Hall effect paper. See the Prospect of quantum anomalous Hall and quantum spin Hall effect in doped kagome lattice Mott insulators paper.
quantum application. See quantum computer application.
quantum approximate optimization algorithm. A quantum algorithm which computes approximate solutions for combinatorial optimization problems. Abbreviated as QAOA. See the A Quantum Approximate Optimization Algorithm paper by Farhi, Goldstone, and Gutmann. See also: quantum alternating operator ansatz.
quantum ascendancy. Synonym for quantum supremacy, quantum preeminence, and quantum advantage. Alternatively, recognizing that quantum computing is rising steadily and rapidly, and at a rate faster than the capacity and performance of classical computers. Although, it’s not abundantly clear that that is the case at this time, yet.
quantum assembly language. A programming language (assembly language) used to express a quantum program or quantum logic circuit in terms of individual quantum logic gates, roughly comparable to a classical assembly language but for a quantum computer. Shortened as QASM. See also: OpenQASM and QUIL. Synonym for assembly language for quantum computers.
quantum assembly language code. Source code written in a quantum assembly language.
quantum-assisted learning. TBD.
quantum-assisted machine learning. TBD.
quantum associative memory. The ability to store patterns and then look up a pattern given only a portion of the pattern, using a neural network to store the patterns based on qubits. See the Quantum Associative Memory paper.
quantum associative memory algorithm. An algorithm for the design of a quantum associative memory.
quantum autoencoder. See quantum autoencoder algorithm. Abbreviated as QAE.
quantum autoencoder algorithm. TBD. Abbreviated as QAE.
quantum automata. The adaptation of the concept of automata to quantum computing. [TBD: more detail] See the Quantum Automata and Quantum Grammars paper. See also quantum language and quantum grammar.
quantum-based technologies. Quantum computing, quantum communication, or any other technology whose primary function is based on quantum mechanics, especially qubits. Referenced in National Quantum Initiative Act bill.
quantum basis. See basis. The set of quantum basis states from which all quantum states are composed, as linear combinations.
quantum basis state. See basis state. One of the quantum states forming a set from which all quantum states are composed as linear combinations.
quantum bath. TBD. See also: bath and open quantum system.
quantum biology. TBD.
quantum bit. The fundamental unit of value on a quantum computer, which may be a superposition of a 0 and a 1, using the quantum states of |0> and |1>, in contrast to the classical bit of a classical computer which can only represent a single value, either a 0 or a 1. Where quantum information is stored. Commonly referred to as a qubit. A single qubit can represent two values simultaneously while a classical bit can only represent a single value at any moment. Two qubits can represent four values simultaneously, a classical bit only two. n qubits can represent 2 to the n values or quantum states simultaneously, while n classical bits can only represent n values (each a single classical bit) at only moment. Qubits can also be entangled. The primary downside to a qubit is that its value cannot be read (measured) without causing its superimposed quantum state to collapse to a single value. Another significant downside is that current quantum technology requires that qubits be chilled to near absolute zero in order to support superposition and entanglement. Alternatively, in the context of quantum communication and quantum teleportation, the quantum state to be teleported. See the Wikipedia Qubit article. See also: qutrit, qudit, stationary qubit, flying qubit.
quantum bit commitment. A protocol for quantum cryptography and quantum communication. [TBD: more detail]. See the Wikipedia Commitment scheme article. See the Quantum bit commitment and the reality of the quantum state paper. Abbreviated as QBC.
quantum braid. A stable configuration of anyon quasiparticles which can be used to construct a qubit for a topological quantum computer. See the Wikipedia Topological quantum computer article.
quantum bus. The equivalent of a classical bus, but for a quantum computer. Interconnections for controlling and interconnecting qubits, including entanglement, such as using microwaves in waveguides. See the Wikipedia Quantum bus article.
quantum C language. A hypothetical variant of the C classical programming language adapted to quantum computing. Proposed by Stephen Blaha in his paper, Quantum Computers and Quantum Computer Languages: Quantum Assembly Language and Quantum C Language. As of June 2018, there is no implementation of this conception.
quantum calibration. See physical qubit calibration.
quantum calculation. See quantum computation, possibly with more of an emphasis on numerical calculation.
quantum cellular automaton. The concept of a cellular automaton adapted to a quantum computer. See the Wikipedia Quantum cellular automaton article. Abbreviated as QCA.
quantum channel. See quantum communication channel.
quantum chaos. See quantum chaos theory.
quantum chaos theory. Classical chaos theory for dynamical systems adapted to quantum mechanics and quantum computing. See the Wikipedia Chaos theory article. See the Wikipedia Quantum chaos article.
quantum charge-coupled device. TBD. Abbreviated as QCCD.
quantum chemist. TBD.
quantum chemistry. TBD.
quantum chemistry simulation algorithm. TBD.
quantum chemistry study. TBD.
quantum chip. An integrated circuit containing one of more qubits and associated circuitry needed to directly control that qubit.
quantum chip interconnect. The physical, mechanical and electrical connection technology used to interface a qubit to the rest of a quantum computer.
quantum circuit. See quantum logic circuit.
quantum circuit abstraction. See quantum logic circuit abstraction.
quantum circuit designer. Someone who conceptualizes and defines quantum circuits — sequences of quantum logic gates. Synonymous with quantum programmer and quantum developer. May also include design of classical computer programs which in turn embody or generate quantum circuits or portions of quantum circuits which may be combined or executed separately to form a complete quantum application.
quantum circuit execution. See quantum logic circuit execution.
quantum circuit generation. See quantum logic circuit generation.
quantum circuit intermediate representation. See quantum logic circuit intermediate representation.
quantum circuit IR. See quantum circuit intermediate representation.
quantum circuit model. See quantum circuit model of computation.
quantum circuit model of computation. The model for performing computation on a quantum computer as a quantum logic circuit which consists of a sequence of quantum logic gates or operations. For a discussion of this model as well as alternatives, see the Quantum Computation Beyond the Circuit Model MIT PhD thesis by Stephen Paul Jordan.
quantum circuit processing. The portion of the logic of a larger algorithm, typically a quantum/classical hybrid algorithm, which is implemented using a quantum circuit. Alternatively, the logic which is implemented by a quantum circuit.
quantum circuit validation. Review and checking of a quantum circuit for logic and consistency issues before it is to be executed.
quantum circulator. A device for controlling the flow of a microwave signal in a quantum computer. This is a microwave circulator, but simply specialized for the needs of a quantum computer. Microwaves are used to control qubits, so careful control of the flow of microwaves is needed to minimize quantum decoherence. See the Physics Synopsis: Quantum Circulators Simplified article (synopsys.)
quantum and classical future. The era when both quantum computing and classical computing are both very relevant, each having its own strengths and own weaknesses. Synonym for classical and quantum future.
quantum/classical hybrid algorithm. See quantum hybrid algorithm. Also written as hybrid quantum/classical computing.
quantum-classical boundary. TBD.
quantum-classical interface. The software and hardware needed for a classical computer to communicate with and control a quantum computer. Alternatively, the electronic circuitry needed to connect classical, binary digital circuitry to a qubit.
quantum cloud service. One or more quantum computers available as a cloud-based service on the Internet. The user connects remotely and queues up a quantum program to be executed remotely when a quantum computer of the given type is available. The user will be notified when quantum program execution has been completed and final results of the quantum computation are available.
quantum co-design. See quantum codesign.
quantum code. A quantum program or quantum circuit as implementation of a quantum algorithm designed to run on a quantum computer, in contrast to classical code designed to execute on a classical computer.
quantum codesign. Codesign for quantum algorithms and quantum computers — collaborative design with the intention of achieving a much more optimal design for both. Quantum algorithms and the quantum computer on which those algorithms will run are designed at the same time, feeding knowledge about the algorithms into design of the quantum computer and knowledge about the quantum computer into design of the quantum algorithms, as well as feedback loops between both design processes. May be referred to simply as codesign or co-design. Also written as quantum co-design.
quantum cognition. An attempt to model the human mind in a quantum-like manner, but not necessarily implying that quantum mechanics is needed to explain the operation of the brain and neurons, although there is that possibility — see quantum mind. See the Wikipedia Quantum cognition article. See the Quantum cognition: a new theoretical approach to psychology paper. See the How ‘Quantum Cognition’ Can Explain Humans’ Irrational Behaviors article from The Atlantic. See the Wikipedia Quantum mind article.
quantum coherence. The ability of a quantum computer to maintain its quantum state without incurring quantum errors or losing at least some of its state over time. Coherence of a quantum computer is practically characterized by the number of quantum logic gates that can be executed before quantum errors begin to occur, or by the elapsed time that it takes that number of gates to be executed. Quantum error correction (QEC) can be used to mitigate quantum decoherence. See also: quantum decoherence. See the Wikipedia Quantum decoherence article. See also: fidelity.
quantum coherence time. The elapsed time before a qubit or a quantum computer loses coherence — the quantum state of qubits begins to deteriorate. Synonym for quantum decoherence time. Shortened as coherence time.
quantum communication. The use of quantum entanglement to communicate over a significant distance. Utilizes a quantum communication channel and quantum memory. See the Quantum communication with photons paper.
quantum communication channel. A communication channel used for quantum communication which is capable of transmitting quantum information and maintaining its quantum state. See the Wikipedia Quantum channel article. Shortened as quantum channel. See also: quantum memory.
quantum communication system. See quantum communication.
quantum complexity theory. Computational complexity theory as applied to quantum computing. The study of how much work a quantum computer must perform to solve a problem of a given size, and how long it would take the quantum computer to complete execution of a given quantum program which solves the problem. See the Wikipedia Quantum complexity theory and Computational complexity theory articles.
quantum composer. An interactive software tool which facilitates construction of quantum logic circuits and quantum programs. The tool itself runs on a user’s personal classical computer, not the eventual quantum computer on which the circuit or quantum program is intended to execute. An example is the IBM Q Experience Quantum Composer, which refers to a created circuit as a quantum score.
quantum computation. Computation on a quantum computer. Execution of the quantum logic gates of a quantum program or quantum circuit, based on quantum code which implements quantum algorithms operating on quantum bits (qubits), which follow from the principles of quantum mechanics, including and especially superposition and entanglement. The essence of quantum computation is the precise control of the quantum states of qubits. See Chapter 6 Quantum Computation by John Preskill of CalTech. See the Wikipedia Quantum computing article. Abbreviated as QC.
quantum computational chemistry. TBD. In contrast to classical computational chemistry.
quantum computational chemistry package. TBD. Such as OpenFermion or Qiskit Aqua.
quantum computational complexity. Computational complexity of a quantum algorithm or quantum program or quantum circuit as computed according to quantum computational complexity theory.
quantum computational complexity theory. TBD.
quantum computational cost. TBD.
quantum computational gate synthesis. The process of transforming quantum logic gates into control of the quantum state of qubits. See the Control aspects of quantum computing using pure and mixed states paper
quantum computational supremacy. See quantum supremacy.
quantum computer. A machine or computer capable of quantum computation. A machine exploiting the principles of quantum mechanics to perform computation in a way that is significantly superior to a classical computer. A computer in which the basic unit of information is a superposition of 0 and 1, and supports entanglement of values. May be either a physical quantum computer or a quantum computer simulator. Generally, the former. See the Wikipedia Quantum computing article. Abbreviated as QC.
quantum computer application. An application for a quantum computer.
quantum computer architecture. The specification of the technology and major components of a quantum computer and how they interact. Including number of qubits, their connectivity, and quantum logic gates which are supported. Would also generally include some sense of performance and limitations, such as coherence and maximum circuit depth.
quantum computers are probabilistic rather than deterministic. The essential distinction between quantum computation and classical computation. Based on quantum mechanics being probabilistic, particularly when superposition is being exploited.
quantum computer chip. An integrated circuit which implements one or more qubits of a quantum computer.
quantum computer design. A combination of the instruction set architecture and the hardware design of a physical quantum computer. A quantum computer simulator will have the former, but not necessarily the latter. Alternatively, the process of producing the design for a quantum computer.
quantum computer engineering. The adaptation and extension of classical computer engineering to the design and construction of the hardware of quantum computers, in contrast to classical computer engineering for classical computers. Includes the implementation of quantum instruction set architectures. See also: quantum computer design, quantum science, and quantum computer science.
quantum computer language. A programming language used for coding of a quantum program or a quantum circuit.
quantum computer modality. See qubit modality.
quantum computer operation. Either a single quantum logic operation or the physical activity of a quantum computer. Alternatively, the human activity needed to keep a quantum computer in operation.
quantum computer processor. The heart of a quantum computer. The quantum computing hardware of a quantum computer which houses the qubits and where quantum logic gates are executed against the qubits. May also be referred to as a quantum information processor. May informally be referred to as the quantum processor, or in context as the processor. Alternatively, sometimes used simply as a synonym for the overall quantum computer.
quantum computer processor operation. See quantum computer operation.
quantum computer program. See quantum program.
quantum computer science. Not yet a defined field of its own. Ultimately, an adaptation and extension of classical computer science to the theory, design, development, and application of software which executes on, interfaces with, or otherwise utilizes a quantum computer, in contrast to classical computer science for classical computers. This includes both quantum programs and software operating in the hybrid mode of operation. Includes the specification and use of quantum instruction set architectures, but not the implementation of the hardware of a quantum computer. See also: quantum science and quantum computer engineering.
quantum computer simulation. See quantum computer simulator.
quantum computer simulator. Software which simulates the operation of a quantum computer on a classical computer, simulating the execution of a quantum program. The quantum program will likely run much slower than on a real quantum computer. It may also execute more correctly, without decoherence, since it is not limited by the physical device limitations of a real quantum computer. See also high-end quantum computer simulator.
quantum computer system. Either a reference to a quantum computer itself or to the entire system, including supporting devices, equipment, apparatus, cabling, shielding, cooling, power, software, etc. See quantum computing system.
quantum computer technology. See qubit technology.
quantum computing. Computing using a quantum computer. All of the activities which surround the use of a quantum computer, from design of quantum algorithms, to development of quantum programs, to execution on a quantum computer, to integration with classical computing, to post-processing of measured results from the quantum computer. And the entire quantum computing ecosystem. See also: quantum computation. Alternatively, includes design and development of the quantum computer itself rather than only the use of the quantum computer. Abbreviated as QC.
quantum computing algorithm. An algorithm designed to exploit the capabilities of a quantum computer. See also: quantum program.
quantum computing application. An application which utilizes a quantum computer. May be either a synonym for quantum computing application software or a problem whose solution can be achieved using a quantum computer.
quantum computing application software. Application software which utilizes a quantum computer. The combination of one or more quantum circuits (quantum programs) and one or more classical computer programs to orchestrate processing for a complete software application. How much of the application is executed directly on the quantum computer vs. a hybrid mode of operation will vary.
quantum computing architecture. The foundation conception and structure of a quantum computer in which computing is based on the fundamental value unit of a qubit, which can be simultaneously in a superposition of the |0> and |1> states, in contrast to binary computing architecture where the value unit is a binary bit which has a value of either 0 or 1. [TBD: link to more detail].
quantum computing capabilities. All features and functions of a quantum computer.
quantum-computing capabilities. See quantum computing capabilities.
quantum computing component. A component which is part of or used with a quantum computer. May be a quantum hardware component or a quantum software component. For example, a qubit, a quantum circulator, or a quantum assembler.
quantum computing concept. Any concept or principle related to quantum computing, such as quantum mechanics, superposition, entanglement, quantum logic gate, quantum circuit, quantum program, preparation, execution, and measurement, among many others. See also: quantum computing principles.
quantum computing device. Either a quantum computer or a quantum computing hardware component.
quantum computing ecosystem. The computing ecosystem for quantum computing. The technology, tools, support infrastructure, vendors, component suppliers, service suppliers, community, and people. And of course the quantum computers themselves.
quantum computing era. The era or period of time which begins with reasonably widespread use of robust and reliable quantum computers, when many organizations have access to commercially-viable quantum computers. Whether quantum ready signals that the era is underway is a matter of debate. Personally, I would say that the very definition of quantum ready indicates that robust quantum computers are not yet available, indicating that the quantum computing era has not yet begun, at least in earnest.
quantum-computing expert. A professional who is widely recognized for their knowledge and expertise in quantum computing.
quantum computing hardware. The hardware for a quantum computer itself. What the vendor will ship when an organization buys a quantum computer. See also: quantum computing software.
quantum computing modality. See qubit modality.
quantum computing platform. Synonym for quantum computer or quantum computing system, emphasizing the features and how they can be used by quantum developers, in contrast to performance or other characteristics which are not directly visible to quantum developers.
quantum-computing platform. See quantum computing platform.
quantum computing principles. The principles of quantum computing and quantum mechanics, especially superposition, entanglement, qubits, quantum logic gates, quantum logic circuits, quantum preparation, quantum execution, quantum measurement, and decoherence. Synonym for principles of quantum computing.
quantum computing project. A project or effort which utilizes a quantum computer.
quantum computing research. All aspects of research into quantum computing, including principles, theory, hardware, instruction set architecture, algorithms, fault tolerance, software, development tools, software tools, and applications.
quantum computing software. All levels of software for quantum computing. The full stack. Operating system, middleware, tools, compilers, editors, packages and libraries, interactive development tools, debugging tools, simulators, analysis tools, etc. And quantum applications.
quantum computing solution. Solution to a problem or opportunity which utilizes a quantum computer.
quantum computing stack. See quantum computing software.
quantum computing system. Both the quantum computing hardware and quantum computing software needed for a quantum computer to execute quantum programs for users, as well as any additional equipment to support the system and connect it to the Internet, so that users can submit quantum programs for execution. Synonym for quantum computer system.
quantum computing solutions. Full, end to end solutions to commercial, industrial, and scientific problems, both quantum computing hardware and quantum computing software. And quantum computing services as well.
quantum computing technology. Any hardware or software relevant to the design, development, construction, deployment, or use of a quantum computer. See also qubit technology.
quantum computing technology ecosystem. The vendors, products, and services which enable and facilitate the conception, theory, design, development, construction, deployment, or use of a quantum computing technology.
quantum computing theory. Formalization of the core principles underlying the functioning of a quantum computer, specifically qubits, with quantum superposition and quantum entanglement, quantum logic operations, quantum logic circuits, quantum logic preparation, quantum logic execution, and quantum logic measurement. [TBD: no solid reference yet?]. See the Wikipedia Quantum computing article. Synonym is theory of quantum computing. See also: quantum computing principles.
quantum computing toolkit. A collection of software tools and software libraries which enable and facilitate the development of quantum programs.
quantum connectivity. See quantum entanglement. See also: connectivity between qubits and connectivity map.
quantum control. The non-quantum hardware and firmware which effects the manipulation of qubits, primarily due to execution of quantum logic gates, such as through microwave pulses or laser pulses.
quantum controlled phase gate. TBD. See the Heralded quantum controlled phase gates with dissipative dynamics in macroscopically-distant resonators paper by Qin, Wang, Miranowicz, Zhong, and Nori. See also: controlled phase gate and heralded quantum controlled phase gate.
quantum convolutional layer. TBD.
quantum core. The innermost subsystem or chip(s) of a quantum computer which contains the qubits. Alternatively, also includes the subsystem which contains all of the control circuitry and other hardware needed for the execution of quantum logic gates.
quantum correlation. TBD. See the Wikipedia Quantum correlation article.
quantum coupling. See quantum entanglement. They are synonyms. See also: qubit coupling.
quantum cryptographic algorithm. See quantum cryptography.
quantum cryptographic method. See quantum cryptography.
quantum cryptography. The use of a quantum computer to perform tasks associated with cryptography, including quantum key distribution, encryption, decryption, and quantum communication. See the Wikipedia Quantum cryptography article. See also: post-quantum cryptography. Alternatively, the use of a quantum computer to crack a cryptographic key. See also: traditional modern cryptography.
quantum data. See quantum information.
quantum data processing inequality. TBD.
quantum decoherence. The tendency of a quantum computer to lose its quantum coherence due to quantum errors, typically due to poor isolation from the surrounding environment. The coherence of a quantum computer is practically characterized by the number of quantum logic gates which can be executed before quantum errors begin to occur, or by the elapsed time that it takes that number of gates can be executed. Quantum error correction (QEC) can be used to mitigate quantum decoherence. See also: quantum coherence. See the Wikipedia Quantum decoherence article. [TBD: expand, add detail, cleanup.] See also: fidelity. See also: quantum coherence time and quantum decoherence time.
quantum decoherence time. The elapsed time before a qubit or a quantum computer loses coherence — the quantum state of qubits begins to deteriorate. Synonym for quantum coherence time. Shortened as decoherence time.
quantum decryption. The use of a quantum computer to decrypt messages.
quantum developer. A software developer or other computer professional, or possibly a scientist or engineer, who engages in the development of quantum programs or quantum logic circuits based on quantum algorithms, which they may or may not have designed or adapted themselves. Usually a member of a project and a team.
quantum development. Development of quantum programs and quantum logic circuits.
quantum development environment. Software tools for quantum development. For example, Forest from Rigetti Computing.
quantum device. Synonym for quantum computer, the raw machine, the hardware. Alternatively, an individual qubit.
quantum device engineer. TBD.
quantum devices without error correction. Quantum computers which do not employ any scheme to mitigate quantum errors. That makes them simpler and faster, but less reliable. This is generally not by choice, but usually the only quantum technology which is available. The common case in 2018. Quantum error correction (QEC) is still limited to the research stage. Alternatively, an individual qubit, emphasizing that it has no quantum error correction.
quantum dot. A very small semiconductor particle exhibiting behavior in between larger semiconductor components and discrete molecules. See the Wikipedia Quantum dot article. Abbreviated as QD. See depletion mode quantum dots and enhancement mode quantum dots.
quantum dot cellular automata. A quantum computer based on a grid or lattice of quantum dots (QD). See the Wikipedia Quantum dot cellular automaton article. See the Quantum Computing with Quantum-dot Cellular Automata using Coherence Vector Formalism paper.
quantum dot cellular automaton. See quantum dot cellular automata.
quantum dot quantum computer. A quantum computer based on quantum dots (QD). See also scalable quantum dot quantum computer. Abbreviated as QDQC. See the Quantum Computation with Quantum Dots paper by Loss and DiVincenzo.
quantum dot technology. Any device based on quantum dots (QD).
quantum ecosystem. See quantum computing ecosystem.
quantum eigenvalue estimation algorithm. See quantum phase estimation algorithm.
quantum enabled project. See quantum-enabled project.
quantum-enabled project. A program, application, or system which uses quantum algorithms and the execution of quantum programs or quantum logic circuits on a quantum computer for some portion(s) of its computation. See also: hybrid mode of operation.
quantum encryption. The use of a quantum computer to encrypt messages and/or decrypt messages. Alternatively, to use a quantum computer to crack an encrypted message.
quantum energy level. The energy level of a quantum system can take on only discrete quantities of energy, a discrete level — the ground state or an excited state. See the Wikipedia Energy level article.
quantum-enhanced feature space. TBD.
quantum enhanced feature space. See quantum-enhanced feature space.
quantum entanglement. Two (or more) qubits (or any particles for quantum mechanics in general) have a combined, shared, common quantum state (entangled state) as if they were a single quantum system and do not have an independent quantum state for each qubit (or particle.) Measurement of an observable of either qubit or particle will necessarily give a value that is identical to that same observable of the other qubit (or particle.) Commonly achieved by a combination of a Hadamard gate (H gate) and a controlled-NOT gate (CNOT gate) — see entangle two qubits. See the Wikipedia Quantum entanglement article. See also: entangle two qubits, connectivity between qubits, and connectivity map.
quantum entanglement detection. Any method used to detect that the quantum states of two qubits are entangled. See quantum entanglement. See the Entanglement detection paper.
quantum entanglement witness. A technique to examine whether a qubit is entangled or not. See the Wikipedia Entanglement witness article.
quantum error. Any deviation from the proper quantum state for a particular qubit or the quantum computer as a whole (all qubits). This may be due to decoherence or stray electromagnetic radiation if the machine is not properly isolated from the surrounding environment. See also: quantum decoherence. See also: quantum error correction (QEC). [TBD: expand, more detail, link.]
quantum error correcting code. See quantum error-correcting codes.
quantum error-correcting codes. Additional qubits in a quantum computer used to compensate for quantum errors roughly analogous to Error-Correcting Code (ECC) memory on a classical computer. Shortened as QECC.
quantum error correction (QEC). Various techniques to compensate for errors in the quantum state of a qubit due to decoherence or stray electromagnetic radiation, such as adding code qubits — see quantum error-correcting codes (QECC). See the Wikipedia Quantum error correction article.
quantum error-correction scheme. See quantum error correction.
quantum error mitigation. Techniques for designing quantum circuits to compensate for qubit errors and gate errors. Abbreviated as QEM. See also quantum error correction (QEC).
quantum error mitigation scheme. See quantum error mitigation.
quantum error mitigation technique. TBD. Abbreviated as QEM.
quantum error rate. The probability that an error will occur when executing a quantum logic gate or operation. 1 in 1,000 or 0.001 for single-qubit operations and 1 in 100 or 0.01 for two-qubit operations is common with quantum computers as of July 2018.
quantum execution. May be either quantum logic gate execution, quantum circuit execution, or quantum program execution.
quantum execution phase. The stage of processing of a quantum circuit or quantum program when execution is performed — quantum logic circuit execution. See also: quantum preparation phase and quantum measurement phase.
quantum experiment. An experiment run on a quantum computer.
quantum factorization. Prime factorization using a quantum computer. Such as to crack an encryption key. See the Quantum factorization of 56153 with only 4 qubits paper by Dattani and Bryans. See also: Shor’s algorithm.
quantum fault-tolerance theorem. See quantum threshold theorem.
quantum fault. See quantum error. There are three stages of execution during which quantum faults may occur: preparation, logic gate execution, and measurement. See faulty quantum logic preparation, faulty quantum logic gate execution, and faulty quantum measurement.
quantum fidelity. See quantum coherence.
quantum field theory. The theoretical framework in theoretical physics that combines classical field theory, special relativity, and quantum mechanics. See the Wikipedia Quantum field theory article. Abbreviated as QFT (which may be confused with quantum Fourier transform.)
quantum finite-state automaton. Adaptation of the concept of a finite-state automaton to quantum computing. Abbreviated as QFA.
quantum finite-state machine. Adaptation of the concept of a finite-state machine to quantum computing. See also: quantum finite-state automaton.
quantum Fourier transform. The discrete Fourier transform adapted to quantum computation. See the Wikipedia Quantum Fourier transform article. Abbreviated as QFT. See also: approximate quantum Fourier transform, banded quantum Fourier transform, and full quantum Fourier transform.
quantum future. Vague, general reference to future years when quantum computing is common and quantum computers are relatively cheap and relatively plentiful, or at least significantly more practical than they are today. A time when it is not uncommon for your average Fortune 500 company to be using quantum computing on a regular and consistent basis. Not necessarily implying that classical computing will have waned to any significant degree. Alternatively, the point where classical computing is essentially fully eclipsed by quantum computing, but not likely soon.
quantum gate. See quantum logic gate.
quantum gate array. Synonym for quantum logic circuit (quantum circuit) or quantum program. Term used by Shor in Polynomial-Time Algorithms for Prime Factorization and Discrete Logarithms on a Quantum Computer.
quantum gate library. See quantum logic gate library.
quantum gate sequence. See quantum logic circuit.
quantum gate set. See quantum instruction set. Alternatively, [TBD: review literature].
quantum gate set tomography. TBD. Abbreviated as GST.
quantum grammar. The adaptation of the concept of a language grammar to quantum computing. [TBD: more detail] See the Quantum Automata and Quantum Grammars paper. See also quantum automata and quantum language.
quantum hardware. The physical hardware of a quantum machine, quantum device, or quantum computer. Alternatively, the hardware for the qubits alone, possibly including the hardware which directly manipulates the qubits (quantum control), and possibly the hardware for quantum logic gate execution, separate from all of the other hardware of a quantum computer.
quantum hardware component. A hardware component which is part of or used with a quantum computer, in contrast to a quantum software component. For example, a qubit or a quantum circulator. Alternatively, only the hardware for the qubits themselves, and possibly the hardware components which directly manipulate the qubits and for quantum logic gate execution.
quantum hybrid algorithm. Algorithm which is split into portions which are classical algorithms and portions which are quantum algorithms, so that portions utilize a classical computer and portions utilize a quantum computer. See hybrid mode of operation. Synonym for quantum/classical hybrid algorithm.
quantum information. Data or information which is held in the quantum state of a quantum system — the qubits of a quantum computer. See the Wikipedia Quantum information article. Alternatively, both quantum computing and quantum communication.
quantum information application. See quantum computer application.
quantum information processing. See quantum computation.
quantum information processing algorithm. See quantum algorithm. Essentially, all quantum information processing is quantum computation.
quantum information processor. Synonym for quantum computer. Alternatively, may be emphasizing only the core processing logic of the hardware (the quantum computer processor or quantum processor) where logic gates are executed against qubits.
quantum information research. All aspects of research into quantum information — both quantum computing and quantum communication. Includes theory, hardware, instruction set architecture, algorithms, fault tolerance, software, development tools, software tools, and applications.
quantum information research community. All quantum information researchers.
quantum information researcher. Professional engaged in quantum information research. Member of the quantum information research community.
quantum information science. Information science adapted to quantum computing. Representing, storing, transmitting, manipulating, creating, transforming, and monitoring information in devices and media which require quantum mechanics to fully explain their behavior. See the Wikipedia Quantum information science article. See also: quantum information theory.
quantum information science and engineering. TBD. Referenced in National Quantum Initiative Act bill.
quantum information science and engineering field. TBD. Referenced in National Quantum Initiative Act bill.
quantum information science and engineering research. TBD. Referenced in National Quantum Initiative Act bill.
quantum information science and technology. TBD. Referenced in National Quantum Initiative Act bill.
quantum information science and technology activities. TBD. Referenced in National Quantum Initiative Act bill.
quantum information science and technology applications. TBD. Referenced in National Quantum Initiative Act bill.
quantum information science and technology industry. TBD. Referenced in National Quantum Initiative Act bill.
quantum information science and technology research. TBD. Referenced in National Quantum Initiative Act bill.
quantum information science and technology research and development. TBD. Referenced in National Quantum Initiative Act bill.
quantum information science and technology research and development programs. TBD. Referenced in National Quantum Initiative Act bill.
quantum information science and technology research and education. TBD. Referenced in National Quantum Initiative Act bill.
quantum information science and technology research, testing, and education. TBD. Referenced in National Quantum Initiative Act bill.
quantum information science and technology workforce. TBD. Referenced in National Quantum Initiative Act bill. See also: quantum information workforce.
quantum information science and technology workforce pipeline. TBD. Referenced in National Quantum Initiative Act bill.
quantum information scientist. TBD.
quantum information theorist. Quantum researcher working in the area of quantum information theory. See also: quantum information research and quantum information researcher.
quantum information theory. See quantum information. See Chapter 5 Quantum Information Theory by John Preskill of CalTech.
quantum information workforce. Professionals working in the field of quantum computing. See also: quantum information science and technology workforce.
quantum-inspired algorithm. Short for quantum-inspired classical algorithm.
quantum-inspired classical algorithm. See quantum-inspired computing technology.
quantum-inspired computing. See quantum-inspired computing technology.
quantum-inspired computing technology. Attempting to apply some of the concepts from quantum computing and quantum algorithms to the development of algorithms designed to execute on classical computers, beyond merely simulating a quantum computer. The goal is to achieve either greater performance or the capacity to handle larger problems than with classical algorithms, or to achieve results that classical algorithms have not been capable of achieving. There is also potential for enhancement of classical computing hardware to better support quantum-inspired computing, possibly using GPUs and FPGAs. Not all quantum computing concepts can be migrated to classical systems, but there is still some potential. This is more of an aspirational concept at this stage than a practical reality. Related terms are quantum-inspired algorithm, quantum-inspired classical algorithm, and quantum-inspired computing. See also: Ewinization.
quantum instruction language. An assembly language for quantum computers. Abbreviated as QUIL. Developed by Rigetti Computing. See the A Practical Quantum Instruction Set Architecture paper by Smith, Curtis, and Zeng.
quantum instruction set. The instruction set or types of quantum logic gates of a quantum computer. See quantum instruction set architecture.
quantum instruction set architecture. A detailed specification of the instruction set architecture of a quantum computer, which is the set of gates, operations, or instructions that a quantum computer can execute, including any internal data and control resources, such as registers and memory which can be accessed by those instructions, as well as any data formats which are relevant to both instructions and internal data and control resources. At present, qubits are the only resources available for access. See also classical instruction set architecture. For an example see the A Practical Quantum Instruction Set Architecture paper from Rigetti Computing.
quantum integrated circuit. Integrated circuit comprised of one or more qubits (qubit circuits). Synonym for qubit chip. See also: non-planar quantum integrated circuit.
quantum interference. TBD.
quantum interference circuit. TBD.
quantum interferometric computation. TBD. Abbreviated as QUIC. Referenced in The role of Quantum Interference in Quantum Computing paper by Shiekh.
quantum intermediate measurement. Quantum measurement performed before the completion of a quantum circuit. The outcome of the quantum intermediate measurement may be used to influence the choice of what quantum logic gates will follow.
quantum kernel method. TBD.
quantum key distribution. A method and protocol based on quantum mechanics for producing and exchanging cryptographic keys between two parties so that they can communicate securely. Abbreviated as QKD. See the Wikipedia Quantum key distribution article. See also: quantum communication.
quantum language. The adaptation of the concept of a language to quantum computing. [TBD: more detail] See the Quantum Automata and Quantum Grammars paper. See also quantum automata and quantum grammar. Alternatively, a quantum programming language.
quantum latency. TBD.
quantum leap. The significant advantage that quantum computing is perceived to have over classical computing in terms of performance and capacity, or at least is expected to have once research is completed and practical obstacles are addressed.
quantum learning. See quantum machine learning.
quantum-like. An approach which is similar or analogous to quantum. Exhibiting at least a passing resemblance to the principles of quantum computing, such as quantum states, superposition, and entanglement. See also quantum-inspired.
quantum-limited amplifier. TBD. See the IBM Q Rising above the noise: quantum-limited amplifiers empower the readout of IBM Quantum systems web page. Abbreviated as QLA.
quantum logic. Any combination of quantum logic gates (or quantum logic operations) designed to perform some computation, ranging from a single gate (operation), to a sequence of gates (operations), to a full circuit (quantum logic circuit) or even a full program (quantum program). In contrast to classical logic. Alternatively, a synonym for quantum algorithm.
quantum logic circuit. A sequence of quantum logic gates specifying quantum logic operations to be applied to the qubits of a quantum computer in the order specified. See also quantum program. Sometimes referred to as a gate sequence or a quantum gate array. The quantum equivalent of a code fragment for a classical computer, although it may indeed be equivalent to a complete classical program.
quantum logic circuit abstraction. The conception of a quantum logic circuit and its operation, as distinct from its physical or simulated realization. The abstract process of executing a quantum logic circuit, from generation, to preparation, to execution, to measurement, and finally to post-processing of results.
quantum logic circuit depth. The number of quantum logic gates in a quantum logic circuit. Synonym for quantum logic gate count, circuit depth, or gate count. The length of a quantum program.
quantum logic circuit execution. Execution of a quantum logic circuit on a quantum computer, either a real quantum computer or a simulated quantum computer, each quantum gate of the logic circuit is executed in the order specified. The circuit may be a complete quantum program, or in the case of hybrid mode of operation, it may be only a portion of a larger collection of circuits which require intervention by classical code before execution can continue. May be referred to as quantum execution, circuit execution, or simply execution. See also: quantum logic gate execution.
quantum logic circuit fidelity. A measure of logic gate errors during the execution of a quantum circuit. See also: cross entropy. For detailed math, see the Characterizing Quantum Supremacy in Near-Term Devices paper. Shortened as quantum fidelity or even fidelity.
quantum logic circuit generation. Generation of a sequence of quantum logic gates from a higher-level language or intermediate representation of a quantum logic circuit or a quantum program. Also referred to as quantum circuit generation or simply circuit generation. Once generated, the circuit is ready for execution.
quantum logic circuit intermediate representation. A data format (code format) which represents the abstract logic of a quantum circuit, but distinct from the exact code format required for execution on a quantum computer. This allows software tools to perform various transformations on the code in this code format before it is finally ready for execution. See also: intermediate representation and intermediate format.
quantum logic circuit measurement. Additional gates placed at the end of a quantum logic circuit to measure the quantum state of the qubits, to select the subset of the quantum state which is considered the results of the circuit. See also: quantum logic circuit preparation.
quantum logic circuit preparation. Additional quantum logic gates placed at the beginning of a quantum logic circuit to initialize the quantum state of the qubits which are the inputs to the main logic of the circuit. See also: quantum logic circuit measurement.
quantum logic circuit step. An individual quantum logic gate or operation in a quantum logic circuit or quantum program. The circuit is a sequence of steps.
quantum logic gate. A single quantum logic operation to be performed on one or two qubits, or on all qubits of a quantum register in parallel. A specification of a specific quantum logic operation. The basic, building block, unit of execution in a quantum computer. A sequence of quantum logic gates are combined into quantum circuits to form quantum programs. In contrast to classical logic gates, which are physical logic gates, a quantum gate is simply an operation rather than a physical gate. Commonly shortened to quantum gate, logic gate, or gate. The common quantum logic gates are controlled (cX cY cZ) gate, controlled-NOT (CNOT) gate, Deutsch (D-theta) gate, Fredkin (CSWAP) gate, Hadamard (H) gate, Ising (XX) gate, Pauli-X gate, Pauli-Y gate, Pauli-Z (R-pi) gate, phase shift (R-phi) gates, square root of NOT gate (SQRT NOT), square root of Swap gate ( SQRT SWAP), and swap (SWAP) gate. See the Wikipedia Quantum logic gate article.
quantum logic gate count. The number of quantum logic gates in a quantum logic circuit. Synonym for quantum logic circuit depth, circuit depth, or gate count.
quantum logic gate error. Execution of a quantum logic gate (operation) fails to give the correct or expected result. Commonly due to quantum decoherence or stray electromagnetic radiation. See also: quantum error.
quantum logic gate execution. Execution of a single quantum logic gate in a quantum logic circuit. This is the unit of execution on a quantum computer. See also: quantum logic circuit execution. May be shortened as logic gate execution or gate execution..
quantum logic gate instruction set. See quantum instruction set.
quantum logic gate library. The collective definitions of any group of quantum logic gates, organized in a form to facilitate the development, compilation, and execution of quantum programs using those gates. See also: commonly used quantum logic gate library.
quantum logic gate sequence. See quantum logic circuit.
quantum logic operation. A logic operation for a quantum computer. In contrast to a classical logic operation for a classical computer. Quantum logical operations are specified as quantum logic gates, and sequences of them are referred to as circuits (quantum logic circuits). Synonym for quantum logic gate. May be referred to as quantum operation, or simply operation, or gate.
quantum logic subcircuit. Portion of a quantum logic circuit. A sequence of quantum logic gates which are part of a larger quantum logic circuit. Synonym for sequence of quantum logic gates.
quantum logical gate. See quantum logic gate. Alternatively, a quantum logic gate being executed on a quantum logical qubit which is implemented as multiple quantum physical qubits for the purpose of quantum error correction (QEC). A quantum logic gate being executed on one of those quantum physical qubits is considered a quantum physical logic gate or physical logic gate for short.
quantum logical qubit. An ideal qubit as seen from the perspective of a quantum instruction set architecture, quantum program, programmer, or user, in contrast to a physical qubit in the underlying hardware. Error correction schemes may require multiple quantum physical qubits to implement each quantum logical qubit. See also: quantum logical gate and quantum physical gate. Shortened as logical qubit.
quantum machine. Synonym for quantum computer. May intend to emphasize the hardware, the physical machine.
quantum machine learning. The artificial intelligence concept of machine learning, applied to quantum computing. [TBD: any special aspects worth noting?]. See the Wikipedia Quantum machine learning article.
quantum machine instruction. See quantum logic gate. Abbreviated as QMI.
quantum matrix inversion. TBD.
quantum machine learning. Machine learning (ML) on a quantum computer. Abbreviated as QML. See also: quantum machine learning algorithm.
quantum machine learning algorithm. An algorithm for machine learning which is optimized for the unique capabilities of a quantum computer. See the Implementing a distance-based classifier with a quantum interference circuit paper by Schuld, Fingerhuth, and Petruccione.
quantum measurement. A request to capture the quantum state of one or more qubits, by executing a quantum measurement logic gate (one per qubit.) Alternatively, the result of such a request. By definition, a measurement will be a real value. This will cause the quantum state of any measured qubits to collapse, to a discrete, specific real value, no longer a superposition of values, so measurement is generally done at the end of a quantum logic circuit, since any superposition of quantum states will be lost. It is effectively a quantum logic gate, but is not a true, reversible quantum logic gate since there will be no way to recreate the previous quantum state solely from the result due to collapse of the wave function. In terms of quantum mechanics, measurement returns a value which is a basis state, |0> or |1>, which is represented by an eigenvector of the eigenstate of the wave function for the qubit, with the eigenvector chosen based on its probability, which is represented by the amplitude (probability amplitude) of the eigenvector which is represented by the eigenvalue associated with that eigenvector. The probability for each eigenvector of a qubit is the square of the modulus of the complex number representing the eigenvalue, the amplitude or probability amplitude, for its associated eigenvector — the sum of the squares of the real part and the imaginary part of the amplitude. The probabilities for each of the eigenvectors for a given qubit must sum to 1.0, by definition, according to the principle of unitarity of quantum mechanics. Shortened as measurement. Synonym for quantum readout. See the Wikipedia Measurement in quantum mechanics article. See also: quantum intermediate measurement and eigenvalues and eigenvectors.
quantum measurement logic gate. A quantum logic gate used to perform quantum measurement.
quantum measurement phase. The stage of processing of a quantum circuit or quantum program when measurement is performed. See also: quantum preparation phase, quantum execution phase, quantum intermediate measurement, and post-processing phase.
quantum mechanical entanglement. Proper term from quantum mechanics for what we call entanglement or quantum entanglement in the context of quantum computing.
quantum mechanical transistor. See quantum transistor.
quantum mechanics. The subfield of physics concerned with motion and interactions at the atomic and subatomic level, including electromagnetic radiation or photons, where the distinction between particles and waves overlaps and is more about probability than certainty and determinism. In contrast to classical or Newtonian mechanics where probability is not needed as certainty and determinism rule. The state of a quantum system is defined or modeled as a wave function which expresses the probabilities of the values of every observable or measurable quality or quantity of the system, where the system might be a single atom, a single electron, or a single photon. Wave functions enable superposition of multiple quantum states for a single particle or wave. This is the foundation science of quantum computing. See the Wikipedia Quantum mechanics article. For a more gentle introduction, see the Wikipedia Introduction to quantum mechanics article. Quantum physics is a synonym.
quantum memory. Method or device for storing quantum information, especially in conjunction with a quantum communication channel. Referenced in the Continuous-Variable Quantum Computing in Optical Time-Frequency Modes using Quantum Memories paper by Humphreys, Kolthammer, Nunn, Barbieri, Datta, and Walmsley. Alternatively, sometimes may include qubits as well.
quantum metrology. TBD. See the Wikipedia Quantum metrology article.
quantum mind. A belief that the behavior of the human mind cannot be explained without the need for quantum mechanics to explain the operation of the brain and neurons. Essentially, that the human brain and mind constitute a quantum computer. See the Wikipedia Quantum mind article. Not to be confused with quantum cognition.
quantum Monte Carlo method. TBD. Abbreviated as QMC.
quantum network. The ability to transmit quantum information — the quantum state of qubits between quantum computers. See the Wikipedia Quantum network article. See also: quantum communication. The concept of networking quantum computers is not feasible with current quantum computers or near-term quantum computers, nor does it seem to be coming any time soon after that, but ultimately it will present some very interesting possibilities.
quantum neural network. The concept of a neural network adapted to quantum computing. Abbreviated as QNN. See the Wikipedia Quantum neural network article.
quantum noise. Any electrical, magnetic, electromagnetic, thermal, acoustic, or vibration effect from either the surrounding environment or from within a system or apparatus itself that has the effect of disrupting the quantum state of a quantum system, such as the qubits of a quantum computer. See the Wikipedia Quantum noise article. See also: decoherence.
quantum non-demolition. TBD. Abbreviated as QND.
quantum non-demolition measurement. TBD. Abbreviated as QND.
quantum nonlocality. The ability of two physically separated quantum systems, such as two qubits, to share their quantum state so that they may interact at a distance, such as with quantum entanglement. See the Wikipedia Quantum nonlocality article.
quantum operation. See quantum logic operation.
quantum operator. In quantum mechanics, a matrix which operates of the quantum state of a quantum system, producing a new quantum state. Mathematically this is simply matrix multiplication. Alternatively, a quantum logic operation, which effectively represents that matrix and effectively implements such a matrix multiplication in hardware.
quantum optics. Quantum mechanics applied to the interaction between light (or other electromagnetic radiation) and matter. See the Wikipedia Quantum optics article.
quantum oracle. TBD.
quantum order finding algorithm. See quantum order-finding algorithm.
quantum order-finding algorithm. A quantum algorithm to find the order of an integer modulo another integer. Also known as the period of the integer. The first integer is raised to successive powers until the remainder when divided by the second integer is 1. The order or period of the first integer is the power. Used primarily for factorization of large integers. The basic algorithm can be simply implemented as a classical algorithm, but its performance (computational complexity) will be exponential (very bad), while the performance of the equivalent quantum algorithm will be polynomial (much better.) This is the core, quantum portion of Shor’s algorithm. There are a number of variations on Shor’s original algorithm. In theory, this is the algorithm which will enable a quantum computer to crack even the strongest public-key encryption. Abbreviated as QOFA. See section 5 of the Polynomial-Time Algorithms for Prime Factorization and Discrete Logarithms on a Quantum Computer paper by Shor.
quantum parallel. TBD.
quantum parallelism. Each quantum logic operation can be applied to all quantum states which are superimposed. [TBD: clarify, explain.]
quantum phase estimation. See quantum phase estimation algorithm.
quantum phase estimation algorithm. Method for calculating an approximation of the phase (fraction of a full circle) for a qubit. See the Wikipedia Quantum phase estimation algorithm article. Alternatively, method for calculation of energy states for real quantum systems, such as for computational chemistry. Shortened as phase estimation algorithm. Abbreviated as QPE or PEA or QPEA. See the A Generalised Variational Quantum Eigensolver paper by Wang, Higgott, and Brierley. See also: variational quantum eigensolver (VQE).
quantum phenomena. See quantum phenomenon.
quantum phenomenon. A phenomenon which occurs in a quantum system and is due to quantum mechanics. Such as superposition, entanglement, collapse of quantum state on measurement, and coherence. [TBD: expand]
quantum photonic computing. TBD. See quantum photonic processor. Synonym for photonic quantum computing.
quantum photonic processor. TBD. See also: on-chip quantum photonic processor. See the Xanadu corporate website.
quantum physical logic gate. A quantum logic gate being executed on a quantum logical qubit which is implemented as multiple quantum physical qubits for the purpose of quantum error correction (QEC). A quantum logic gate being executed on one of those quantum physical qubits is considered a quantum physical logic gate or physical logic gate for short. See also: quantum logical gate.
quantum physical qubit. Either the hardware implementing a qubit or one of a collection of qubits which collectively represent a single quantum logical qubit for the purpose of quantum error correction (QEC). See also: quantum physical logic gate.
quantum physics. See quantum mechanics. They are synonyms.
quantum physics of coherent superposition and entanglement. TBD.
quantum physics simulator. A simulator which can simulate the quantum mechanics (quantum physics) of a physical system, both of individual particles and waves, and interactions between them. Not to be confused with a quantum computer, which is simply using quantum mechanics to implement the functions of quantum logic gates. That said, in theory, even a quantum computer could be simulated with a quantum physics simulator.
quantum post processing. Processing (post-processing) of quantum measurements which occurs on a classical computer after completion of execution of a quantum program on a quantum program. See post-processing phase.
quantum preeminence. See quantum ascendency, quantum advantage, and quantum supremacy. The stage at which quantum computing is clearly superior to classical computing for a reasonably wide range of applications. Alternatively, the stage when quantum computing is clearly superior to classical computing for one or more reasonably wide niche of applications, even if short of preeminence across all niches.
quantum preparation. See quantum preparation phase.
quantum preparation phase. The stage of processing of a quantum circuit or quantum program when preparation is performed, the initialization of the quantum state of the qubits which are the inputs to the main logic of the circuit. See also: quantum execution phase, quantum measurement phase, and post-processing phase. Synonym for quantum state preparation.
quantum probabilistic grammar. A quantum grammar, with probabilities for each grammar rule. See the Quantum Computers and Quantum Computer Languages: Quantum Assembly Language and Quantum C paper by Stephen Blaha.
quantum probability. TBD. See quantum probability theory. Alternatively, a reference to the probabilistic nature of quantum computing.
quantum probability theory. TBD. See the Introduction to Quantum Probability paper by Swart and the Quantum Probability Theory paper by Redei and Summers.
quantum process tomography. TBD. Abbreviated as QPT. See also quantum state tomography and output state tomography.
quantum processing unit. See quantum processor. Abbreviated as QPU.
quantum processing unit element. The individual electronic components or electronic devices which collectively comprise a single qubit or entire quantum processing unit (or quantum processor or even quantum computer.) This includes Josephson junctions, superconducting loops, and resonators. Shortened as QPU element.
quantum processor. The heart of a quantum computer which houses the actual qubits and where quantum logic gates are executed. More properly referred to as the quantum computer processor. Alternatively, it may simply be a synonym for the overall quantum computer. See also: quantum processing unit.
quantum processor noise. See quantum noise.
quantum program. The full sequence of quantum logic gates in a quantum circuit specifying the sequence of quantum logic operations to be performed on the qubits of a quantum computer. Alternatively, for the hybrid mode of operation, a larger collection of quantum circuits, each of which may be selectively and conditionally executed under the control of a classical computer controlling the quantum computer. A quantum circuit begins with logic gates which perform preparation (quantum logic circuit preparation), initializing the quantum state of the qubits which are the inputs to the main logic of the quantum circuit, and is followed by logic gates which perform measurement (quantum logic circuit measurement), to retrieve the portions of the quantum state which are considered the results or final results.
quantum program execution. Execution of a quantum program on a quantum computer, either a real quantum computer or a simulated quantum computer. A program can be either a single quantum circuit or for the hybrid mode of operation it can be a larger collection of quantum circuits, each of which may be selectively and conditionally executed under the control of a classical computer controlling the quantum computer. For each circuit, each quantum gate of the circuit is executed in the order specified. May be referred to as quantum execution, quantum circuit execution, or simply execution.
quantum programmer. Software developer who specializes in quantum programming. See also: quantum algorithm designer.
quantum programming. The design and coding of quantum programs and quantum logic circuits. A tedious and difficult process at present, except for the most trivial of quantum programs. There are a variety of tools, but design of quantum algorithms is the biggest challenge. See also: quantum programming language.
quantum programming language. Programming language used to express quantum programs, detailing the quantum logic operations to be performed, although higher-level constructs may be used that will be automatically translated into specific quantum logic operators, in contrast to a classical programming language. A quantum programming language may also include traditional classical computing features to allow a hybrid of classical computing and quantum computing, such as classical data structures and classical control structures. See the Wikipedia Quantum programming article. See the Quantum Programming Languages Survey and Bibliography paper, vintage 2005, but giving a decent historical perspective.
quantum-proof. Cryptographic methods which cannot be cracked with a quantum computer, such as with Shor’s algorithm for factoring very large numbers such as public keys. See also: post-quantum cryptography, quantum-safe and quantum-resistant.
quantum property. Any of the physical quantities or properties and behavior of a quantum system according to the principles of quantum mechanics, each of which is an observable which can be detected or measured, including mass, energy, velocity, linear momentum, angular momentum, and spin.
quantum qubit. Redundant — quantum bit or qubit.
quantum readout. Synonym for quantum measurement. Shortened as readout.
quantum ready. Primarily a marketing term. Forward-looking organizations are looking at and experimenting with quantum computing, even though its is not yet ready for production deployment in real-world applications, particularly when it comes to fault-tolerance. See quantum readiness. Alternatively, the second meaning of quantum readiness — current quantum computers are indeed ready for general purpose and real-world applications, including fault-tolerance. See the IBM Getting the World Quantum Ready blog post.
quantum random access memory. Modeling a random access memory (RAM) on a quantum computer. Abbreviated as qRAM or sometimes as QRAM. See the Quantum random access memory and Architectures for a quantum random access memory papers by Giovannetti, Lloyd, and Maccone.
quantum readiness. Primarily a marketing term. No, it doesn’t mean that the technology of quantum computing is ready for general purpose and real-world applications, including fault-tolerance, today, but simply that the technology is evolving rapidly and has shown enough promise and enough actual reality, that forward-looking and forward-leaning organizations should be starting to ramp up their learning, research, and experimenting with the nascent technology so that when the technology is eventually actually ready for general purpose and real-world applications, including fault-tolerance, they can be ready with it, rather than being behind the curve. Alternatively, a metric for how ready any particular quantum computing technology is for actual deployment in general purpose and real-world applications, including fault-tolerance. See the IBM Getting the World Quantum Ready blog post. See also: commercial-availability stage.
quantum register. A sequence of qubits considered as a single unit, which can represent up to 2 to the n distinct values simultaneously via superposition, where n is the number of qubits, in contrast to a classical register which can represent only a single value at any moment out of 2 to the n possible values. See also: n-bit quantum register.
quantum repeater. TBD. Referenced in the Universal holonomic quantum gates over geometric spin qubits with polarised microwaves paper by Nagata, Kuramitani, Sekiguchi, and Kosaka.
quantum representation. TBD.
quantum research. Research in the fields of quantum computing and quantum communication. See also: quantum researcher, quantum research community, and quantum information research.
quantum research community. All quantum researchers. See also: quantum information research community.
quantum research and development. See quantum research. Referenced in National Quantum Initiative Act bill.
quantum research and education. TBD. Referenced in National Quantum Initiative Act bill.
quantum researcher. Researcher in quantum research. See also: quantum information researcher, quantum information theorist, and quantum research community.
quantum-resistant. See quantum-resistant cryptography.
quantum-resistant algorithm. A cryptographic algorithm which cannot be cracked with a quantum computer, such as with Shor’s algorithm for factoring very large numbers such as public keys. See quantum-resistant cryptography.
quantum-resistant cryptography. Cryptographic methods which cannot be cracked with a quantum computer, such as with Shor’s algorithm for factoring very large numbers such as public keys. See also: post-quantum cryptography, quantum-safe cryptography, quantum-proof, quantum-safe.
quantum-resistant public-key cryptographic algorithm. See quantum-resistant algorithm.
quantum resource. A capability or physical property of a qubit, especially superposition and entanglement, which can be exploited for quantum computation. [TBD: interference as well? Anything else? Are states resources as well? Amplitude? Phase? Also, term should probably refer to exploiting any quantum mechanical system, not just a qubit and quantum computation.]
quantum revolution. Vague hyperbole, loosely referring to the perceived advantage which quantum computing will have over classical computing once research is complete and practical obstacles are overcome. Alternatively, refers to each significant advance in research and practice for quantum computing. See also: next quantum revolution.
quantum-safe. A cryptographic method which cannot be cracked with a quantum computer, such as with Shor’s algorithm for factoring very large numbers such as public keys. See also: quantum-safe cryptography, post-quantum cryptography, quantum-resistant cryptography, quantum-proof, and quantum-resistant.
quantum-safe cryptography. A cryptographic method which cannot be cracked with a quantum computer, such as with Shor’s algorithm for factoring very large numbers such as public keys. See also: post-quantum cryptography, quantum-resistant cryptography, quantum-proof, and quantum-resistant.
quantum science. Not currently a defined field of its own. Still divided between the fields of physics, computer science, and electrical engineering. Alternatively, any and all aspects of the science of physics, computer science, engineering, and mathematics which are focused on and relevant to the theory, design, construction, and application of quantum computers. Includes both hardware and software. See also: quantum computer science and quantum computer engineering.
quantum score. A quantum circuit or quantum program which has been created using a quantum composer, such as the IBM Q Experience Quantum Composer.
quantum search. TBD. See also: Grover’s algorithm.
quantum search algorithm. TBD. See also: Grover’s algorithm.
quantum sensor. A device (sensor) capable of detecting or measuring quantum properties, such as the properties of a single photon, a single electron, or a single atom. See the Wikipedia Quantum sensor article. See the NIST Quantum Sensors web page. See the Quantum sensing paper by Degen, Reinhard, and Cappellaro.
quantum signal processing. TBD.
quantum silicon chip. Implementation of a quantum computer, particularly qubits, using standard silicon semiconductor integrated circuit technology, nothing exotic. Still requires superconductor chilling, so this does not imply operation at room temperature.
quantum simulator. See quantum computer simulator. Alternatively, a programmable quantum simulator used to simulate a physical system, to simulate the actual physics.
quantum simulation. See quantum computer simulation. Alternatively, programmable quantum simulation to simulate a physical system, to simulate the actual physics. For the latter, see the Using Quantum Computers for Quantum Simulation paper by Brown, Munro, and Kendon.
quantum simulation algorithm. An algorithm for quantum simulation. Context will be required to determine if this is intended as simulation of a quantum computer or simulation of the quantum properties of an arbitrary quantum system.
quantum simulation of chemistry. TBD.
quantum skeptic. Individual who does not accept the feasibility or practicality of quantum computers. Alternatively, an individual who accepts the long-term prospect of quantum computing, but not in the next ten or more years. Alternatively, an individual who accepts the potential for both long and near-term quantum computing, but simply does not accept claims that such a goal has actually been achieved by current efforts, such as due to too few qubits or insufficient coherence.
quantum software. Any software suitable for use with a quantum computer, including quantum software tools, quantum applications, and quantum programs.
quantum software component. A software component which is part of or used with a quantum computer. For example, a quantum assembler.
quantum software library. A software library of reusable quantum software components.
quantum software and machine learning. See quantum software and quantum machine learning.
quantum software and quantum machine learning. Use of quantum computation for machine learning and other aspects of artificial intelligence. Abbreviated as QSML.
quantum software tool. Any software tool suitable for use with a quantum computer.
quantum solution. A solution to a problem or opportunity which applies the principles of quantum computing.
quantum source. TBD.
quantum source of information. TBD.
quantum speedup. A somewhat vague term indicating some measure of how much faster a quantum computer is, might be, could be, or might eventually be than the best classical computers at solving a particular problem or class of problem. Alternatively, the degree to which the rate of computational complexity for a quantum algorithm grows more slowly than a classical algorithm for the same problem as the size of the input grows — that Big O for the quantum algorithm is smaller than Big O for the comparable classical algorithm, such as polynomial vs. quadratic, linear vs. polynomial, square root or logarithmic vs. linear, etc. See the Defining and detecting quantum speedup paper by Rønnow, Wang, Job, Boixo, Isakov, Wecker, Martinis, Lidar, and Troyer.
quantum stack. All levels of quantum computing, from the lower levels of hardware, including the physics and chip design, to the upper levels of software, including tools and applications. See also: full-stack quantum.
quantum state. The probability distribution for every possible observable and measurable quality of the particles and waves in an (isolated) quantum system. Represented by the wave function for the quantum system. Each quantum state is a linear combination of the quantum basis states of the quantum system, which are |0> and |1> for a qubit. A quantum basis state will be a complex vector on the surface of a Bloch sphere. A quantum state can be a superposition of two quantum basis states, each of which will be a complex vector in a Bloch sphere. Any number of quantum states can be combined linearly into multiple complex vectors in a Bloch sphere. The modulus or magnitude of each complex vector in the quantum state is the amplitude or probability amplitude for that complex vector. The amplitude (probability amplitude) for a complex vector in the quantum state represents the square root of the probability of the quantum system being in the quantum state represented by the corresponding basis state or basis vector. The sum of the probabilities for all basis states or basis vectors in the quantum state will be 1.0, as required by the principle of unitarity. A linear combination of two or more quantum states will reduce the amplitude (probability amplitude) applied to each basis vector, so that the sum of the probabilities (square of the modulus of the amplitude) for the basis vectors remains 1.0, as required for unitarity. Quantum state can be modeled for individual qubits or for all qubits of a quantum computer, or any subset of qubits, for that matter. A quantum state whose complex vector is on the surface of the Bloch sphere is known as a pure state — it is simply a rotation of a basis state, |0> or |1>. A quantum state whose complex vector is inside of the Bloch sphere is known as a mixed state — it is is linear combination of basis states, which reduces the amplitudes for each of the combined basis states. See the Wikipedia Quantum state article.
quantum state is entangled. Whether the quantum states of two qubits are entangled.
quantum state leakage. TBD.
quantum state preparation. See quantum preparation phase.
quantum state tomography. TBD. Abbreviated as QST. See also quantum process tomography and output state tomography.
quantum superdense coding. Achieving a higher density with quantum communication by exploiting quantum entanglement. See the Wikipedia Superdense coding article. See the Superdense Coding with GHZ and Quantum Key Distribution with W in the ZX-calculus paper by Anne Hillebrand. Also referred to as superdense coding or quantum dense coding.
quantum superposition. See quantum superposition principle.
quantum superposition principle. The principle of quantum mechanics which allows a single quantum property to be in more than one quantum state at the same time. This is one of the key factors enabling quantum computers. It is what permits a qubit to have a value of both a 0 and a 1 at the same time. See the Wikipedia Quantum superposition and Quantum computing articles. Also referred to as simply superposition.
quantum support vector machine. TBD. Abbreviated as quantum SVM.
quantum support vector machine algorithm. TBD. Abbreviated as quantum SVM algorithm.
quantum supremacy. A quantum computer is able to compute a solution to a particular problem when no classical computer is able to do so — or at least not in some reasonable amount of time or with a reasonable number of classical computers. Does not imply either an advantage or supremacy for any other problems beyond the particular problem or niche of closely related problems. Implies quantum advantage. Alternatively, quantum advantage across a broad range of applications and categories of computations, rather than limited to a particular problem or niche of closely related problems. May also be merely a synonym for quantum advantage unless clear from context. A synonym for quantum computational supremacy, quantum preeminence, or quantum ascendency. See the Wikipedia Quantum supremacy article and the Characterizing Quantum Supremacy in Near-Term Devices paper by Boixo, et al. See more discussion in the What Is Quantum Advantage and What Is Quantum Supremacy? paper. Also see the definition and discussion in the Quantum computing and the entanglement frontier paper by Preskill.
quantum supremacy in the presence of errors. A quantum computer may indeed be faster and handle a larger problem than a classical computer, but quantum errors and the overhead needed to mitigate those errors can diminish or even eliminate that quantum supremacy, so quantum supremacy must take into account the negative impact of mitigation of errors. See the Achieving quantum supremacy with sparse and noisy commuting quantum computations paper by Bremner, Montanaro, and Shepherd.
quantum supremacy test. There is no universally agreed upon benchmark test for what exactly constitutes quantum supremacy. This paper, Characterizing Quantum Supremacy in Near-Term Devices, is one proposal for a quantum supremacy test. See also: practical quantum supremacy test.
quantum SVM. Short for quantum support vector machine.
quantum SVM algorithm. Short for quantum support vector machine algorithm.
quantum system. In quantum mechanics, a collection of matter and energy, particles and waves, of interest, to be studied, analyzed, or used for some purpose or effect. Presumed to be effectively isolated from the surrounding environment. Such a system has a quantum state and a wave function. A quantum system is a vector space where every vector is a linear combination of the basis vectors of that vector space, with quantum states being vectors and quantum basis states being basis vectors. See the Wikipedia Quantum system article. Alternatively, a synonym for quantum computer or quantum computer system.
quantum technology. Any hardware or software needed to develop and build a quantum computer or a quantum communication device.
quantum technologies. See quantum technology.
quantum teleportation. Transmission of the quantum state of a quantum system (a particle or photon) over some extended distance, typically for quantum communication. Sort of a misnomer since the actual particle or photon is not physically transmitted. See the Wikipedia Quantum teleportation article.
quantum theorist. TBD.
quantum theory. See quantum mechanics. See also: quantum computing theory.
quantum thinking. Re-thinking classical problems to come up with quantum solutions.
quantum threshold theorem. The claim that quantum error correction can be successful if the physical error rate for quantum logic gates is below some threshold. See the Wikipedia Quantum threshold theorem article. Also known as the quantum fault-tolerance theorem.
quantum to classical transition. See quantum-to-classical transition.
quantum-to-classical transition. The boundary or gray zone between physical systems which are small enough that quantum effects dominate and systems which are large enough that quantum effects vanish and classical effects dominate. Some quantum effects may remain even for systems of large sizes, and some classical effects may be present even for the smallest systems.
quantum tomography. See quantum state tomography, quantum process tomography, and output state tomography.
quantum transistor. A transistor which exploits the principles of quantum mechanics. See the Wikipedia Tunnel field-effect transistor and Quantum tunnelling articles. See the article on quantum mechanical transistors by Sandia Labs. See also: Josephson junction. Alternatively, a loose reference to a superconducting quantum interference device (SQUID), commonly as more of a marketing term.
quantum tunneling. In quantum mechanics, the potential for a particle or wave to cross a barrier such as an insulator. See the Wikipedia Quantum tunnelling article. See also: Josephson junction.
quantum Turing machine. A hypothetical equivalent of the concept of a Turing machine of classical computing applied to quantum computing. 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 June 2018. See the Wikipedia Quantum Turing machine article. See the Quantum Turing Machines Computations and Measurements paper by Guerrini, Martini, and Masini. Shortened as QTM. See also: universal quantum Turing machine.
quantum utility crossover point. TBD.
quantum value. The value of a qubit, which may be a superposition of 0 and 1, or |0> and |1>, technically, in contrast to the binary value of a classical bit, which is either 0 or 1.
quantum variational algorithm. An algorithm for simulating a physical system on a quantum computer, such as computational chemistry. See also: quantum phase estimation algorithm and variational quantum eigensolver (VQE). See the Towards Practical Quantum Variational Algorithms paper by Wecker, Hastings, and Troyer.
quantum virtual machine. See quantum simulator. Abbreviated as QVM.
quantum volume. A method to judge and benchmark the power and usefulness of a quantum computer. A figure of merit for the power of a quantum computer which is independent of the specific physical technology used to implement the hardware and neutral with respect to the particular architecture of the quantum computer. See the Quantum optimization using variational algorithms on near-term quantum devices paper by Moll, Barkoutsos, Bishop, and Chow, et al of IBM. They propose that the figure of merit be based on five factors: 1) number of qubits, 2) connectivity between qubits, 3) number of logic gates (operations) which can be executed before errors or decoherence become problematic, 4) range of operations in the logic gate instruction set, and 5) number of operations which can be executed in parallel. For a brief summary, see the IBM Increase your quantum IQ blog post. My note: I see no mention of the speed of executing logic gates, which I think should matter a lot.
quantum walk. TBD. See continuous-time quantum walk and discrete-time quantum walk. See the Wikipedia Quantum walk article.
quantum walk operator. TBD.
quantum watchdog. TBD. Synonym for quantum Zeno. Referenced in the Polynomial-Time Algorithms for Prime Factorization and Discrete Logarithms on a Quantum Computer paper by Shor.
quantum wave function. See wave function.
quantum world. See quantum computing era. A world in which quantum computing in commonplace rather than being a novelty.
quantum Zeno. See quantum watchdog.
quanvolutional. Quantum computing equivalent of convolutional.
quanvolutional circuit. TBD.
quanvolutional filter. TBD.
quanvolutional layer. TBD.
quanvolutional neural network. TBD. Abbreviated as QNN.
quasi-lumped element resonator. Electronic component (resonator) used to read a qubit, at least on the Rigetti Computing QPU. See The Quantum Processing Unit (QPU) doc. See also: dispersive readout of a qubit.
quasiparticle. The complex nature of a particle moving through a solid, such as an anyon, which does not behave as a normal particle. Has the potential to be used to construct a qubit. See the Wikipedia Quasiparticle article.
qubit. The fundamental unit of value in a quantum computer, which may be a superposition of 0 and 1, or |0> and |1>, technically, in contrast to a classical bit, which is either 0 or 1. Shorthand for quantum bit. There are four main types of qubit at the hardware level: charge qubit, flux qubit, phase qubit, and spin qubit. A qubit has a dimensionality of two, meaning its quantum states are modeled by a Hilbert space (vector space) with two dimensions, and n qubits modeled by a Hilbert space with a dimensionality of two to the n. Alternatively, in the context of quantum communication and quantum teleportation, the quantum state to be teleported. See the Wikipedia Qubit article. See also: qutrit, qudit, stationary qubit, flying qubit.
qubit anharmonicity. See anharmonicity of a qubit.
qubit bias. TBD.
qubit calibration. See physical qubit calibration.
qubit capacitance. TBD.
qubit chip. An integrated circuit which implements one or more quantum bits at the hardware level. Synonym for quantum integrated circuit. See also: qubit circuit.
qubit circuit. Electronic circuit for one or more qubits. Typically on an integrated circuit (quantum integrated circuit or qubit chip).
qubit coherence. The ability of a qubit to maintain its quantum state for an extended period of time, in contract with qubit decoherence, the tendency for the quantum state of a qubit to deteriorate relatively rapidly. See also: qubit fidelity and quantum coherence.
qubit connectivity. How many and specifically which other qubits a given qubit can be connected to, either to execute a two-qubit gate or to perform quantum entanglement. Alternatively, the aggregate qubit connectivity of all qubits of a given quantum computer. See also: qubit coupling.
qubit control. The physical processes and controlling electronic circuits which enable quantum logic gates to be executed, resulting in the manipulation of the quantum state of a qubit. Such as the use of microwave pulses.
qubit count. The number of qubits in a particular quantum computer.
qubit coupling. See quantum entanglement. Two qubits which are coupled have quantum states which are entangled.
qubit decoherence. The inability of a qubit to maintain its quantum state for an extended period of time, in contract with qubit coherence, the ability for the quantum state of a qubit to persist for an extended period of time. See quantum decoherence.
qubit detuning. TBD.
qubit fidelity. See qubit coherence, quantum fidelity, quantum coherence, and qubit quality.
qubit fragility. The susceptibility of a qubit to having its value, its quantum state, disrupted by quantum decoherence or stray electromagnetic radiation (EMR). Shielding is required. See also: qubit coherence, qubit decoherence, and qubit fidelity.
qubit frequency bias transfer function. TBD.
qubit layout. TBD.
qubit modality. See qubit technology.
qubit nonlinearity. TBD.
qubit physical representation. The specific physical phenomenon or device used to implement a qubit at the hardware level in a particular quantum computer design. See the Wikipedia Qubit article. There are four main types of qubit at the hardware level: charge qubit, flux qubit, phase qubit, and spin qubit.
qubit quality. An overall measure of how well a qubit can perform its intended functions. This includes degree of connectivity to other qubits, error rate for gate execution, coherence time, and speed of gate execution. This also includes how long a qubit can maintain a state of superposition or entanglement. Distinct from qubit count, which is quantity rather than quality.
qubit-qubit coupling. See quantum entanglement and quantum coupling.
qubit-qubit coupling strength. TBD.
qubit-qubit effective frequency shift. TBD. Referenced in The Quantum Processing Unit (QPU) doc by Rigetti Computing.
qubit-qubit frequency detuning. TBD.
qubit readout. Synonym for quantum measurement. Another synonym is quantum readout.
qubit readout error. TBD. May be shortened as readout error.
qubit state. Quantum state of a qubit. Alternatively, each of the superimposed states which collectively comprise the quantum state of a qubit.
qubit technology. The hardware used to implement a qubit, along with the theory behind it, and the manufacturing processes needed to produce it.
qubit transition frequency. TBD. Referenced in The Quantum Processing Unit (QPU) doc by Rigetti Computing.
qubit witness. See quantum entanglement witness.
qubitization. TBD.
QUBO. Initialism for quadratic unconstrained binary optimization problem.
QUBO problem. Short for quadratic unconstrained binary optimization problem. Common application for the D-Wave special-purpose quantum computer.
qubyte. A collection of eight independent qubits which are used in quantum computations as a quantum register, as if they were a classical 8-bit register, although each qubit has its own quantum state which may or may not be entangled with the quantum state of any of the other qubits of the quantum register or other qubits. Alternatively, a single qubit capable of being in 256 distinct quantum states simultaneously. Alternatively, eight qubits, equivalent to a byte on a classical computer. This is a contrived, speculative term as there are no current quantum computers or near-term quantum computers which can process a so-called qubyte as other than eight independent qubits. Note that this is not a commonly used term, for either or any other meaning — for now, it’s an improper term.
qudit. Like a qubit, but with 10 or more discrete quantum states, all of which may be superimposed. A qudit has a dimensionality of ten, meaning its quantum states are modeled by a Hilbert space (vector space) with ten dimensions, and n qudits modeled by a Hilbert space with a dimensionality of ten to the n. Two qudits would represent 100 (10 times 10) simultaneous states, more than the 64 states which six qubits can represent simultaneously. The 1,000 simultaneous states of three qudits would be comparable to the 1,024 simultaneous states of ten qubits. See the IEEE Qudits: The Real Future of Quantum Computing? article. A qudit has a dimensionality of ten, meaning its quantum states are modeled by a ten-dimensional Hilbert space (vector space.). See also: qutrit and qubit. Technically, a qudit can have any dimensionality of ten or higher, so read the above as if “ten” were the actual value of “d”, the intended dimensionality. Alternatively, a d-level quantum system where the letter d implies any number (integer), but typically not 2 — and not necessarily 10. This is more common for photonic quantum computers and sometimes or generally is really simply an alternative term for qumode.
query. A request for information, such as a database query. An expression of the criteria to be used to select the subset of information desired.
queue. A list or line with a front or first item and an end or last item. New items are added to the list at the end while items are removed from the front of the list. The queue can grow and shrink, allowing addition and removal of items to be asynchronous, allowing two processes to cooperate without a need to be absolutely synchronized.
queued-work model. When potentially many users require access to a limited resource, a queue must be created and maintained so that requests from users must be added to the end of the queue and wait until those requests for the resource will be granted as the queue is worked off as the requests at the front of the queue are removed from the queue as they are satisfied.
QUIC. Initialism for quantum interferometric computation.
QUIL. Initialism for quantum instruction language.
qumode. Equivalent to a qubit for a quantum photonic processor designed by Xanadu. Information is stored as a continuous variable.
qutrit. Like a qubit or a qudit, but with three quantum states, |0>, |1>, and |2>, all of which may be superimposed. A qutrit has a dimensionality of three, meaning its quantum states are modeled by a Hilbert space (vector space) with three dimensions, and n qutrits modeled by a Hilbert space with a dimensionality of three to the n. See also: qubit and qudit. See the Wikipedia Qutrit article.
QVM. Initialism for quantum virtual machine.

To browse other parts of the glossary:

Quantum Computing Glossary — Part 4 — Q

Q

Written by Jack Krupansky