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Quantum Computing Glossary

A glossary of terms related to quantum computing for beginners.
© Keio University




  • AIST: The National Institute of Advanced Industrial Science and Technology (JAPAN) [4.22]
  • ARPANET: The Advanced Research Projects Agency Network (ARPANET) was an early packet switching network and the first network to implement the protocol suite TCP/IP. Considered the most important precursor to today’s Internet. [4.22], [4.23]
  • Aspect, Alan: French physicist. [1.5], [2.10], [3.23], [4.21], [4.28]


  • Bacon, Dave: Staff Software Engineer at Google. Prior to Google he was a research assistant professor at the University of Washington. [4.15], [4.28]
  • beam splitters: An optical device that splits a beam of light in two. [4.5], [4.27]
  • beating: The beating of a signal is the low-frequency increase and decrease in amplitude caused by constructive and destructive interference of two waves with slightly different frequencies. [1.18]
  • Bell pairs: A Bell pair is a maximally entangled pair of qubits, useful for quantum teleportation or testing Bell’s inequality. [2.10], [2.13], [2.15], [2.24], [4.27]
  • Bell, John: Northern Irish physicist, and the originator of Bell’s theorem, an important theorem in quantum physics regarding hidden variable theories. [1.5], [2.10], [4.10], [4.15], [4.23], [4.28]
  • Bell’s inequality: Bell’s theorem is a “no-go theorem” that draws an important distinction between quantum mechanics (QM) and the world as described by classical mechanics. [2.10], [4.28]
  • Bell’s theory: Bell’s theorem is a “no-go theorem” that draws an important distinction between quantum mechanics (QM) and the world as described by classical mechanics. [1.5]
  • Benioff, Paul: Paul Benioff is credited with first applying quantum theory to computers in 1981 (Argonne National Laboratory, US). [1.5]
  • Bennett, Charles: One of the founders of the field of quantum information and computation (IBM, US) [1.5], [2.13], [2.14], [4.15], [4.23], [4.28]
  • big data: Term for data sets that are so large or complex that traditional data processing application software is inadequate to deal with them. [1.13], [2.18], [3.19]
  • binary: Relating to, using, or denoting a system of numerical notation that has 2 rather than 10 as a base. [2.7], [2.22], [2.23], [4.13]
  • bit: A unit of information in a computer that must be either 0 or 1. [1.3], [1.20], [2.2], [2.3], [2.4], [2.5], [2.7], [2.14], [3.14], [3.22], [4.12], [4.13], [4.14], [4.15], [4.20], [4.27], [4.28], [4.29]
  • bit flip gate: A bit flip is the change of a bit from 0 to 1, or 1 to 0. [4.12], [4.13], [4.14], [4.15], [4.20]
  • Bloch Sphere: Geometrical representation of the pure state space of a two-level quantum mechanical system (qubit), named after the physicist Felix Bloch. [2.3], [2.5], [2.14], [2.15], 4.2
  • Bloch, Felix: Swiss-born American physicist who shared (with E.M. Purcell) the Nobel Prize for Physics in 1952 for developing the nuclear magnetic resonance method of measuring the magnetic field of atomic nuclei. [2.3], [2.11], [2.14]


  • Caltech: California Institute of Technology. [1.9], [2.7], [2.9], [2.14], [4.10], [4.28]
  • CNOT gate: Controlled NOT gate.the controlled NOT gate is a quantum gate that is an essential component in the construction of a quantum computer. [2.14], [2.15], [2.18], [2.22], [3.14], [4.7], [4.9], [4.14], [4.15]
  • code words: In error correction, a code word is a set of bits that represents a correctly-encoded message. The code word usually consists of more bits than the original message, with reduncancy added for error recovery. [4.12], [4.15]
  • Cooper pair : A pair of electrons, of opposite spin, that are thought to be the basis of superconductivity according to BCS theory. [2.25], [2.28]
  • CREST: CREST is a funding program for team-oriented research with the aim of achieving the strategic goals set forth by the govermment. [4.22]
  • cryostat: A cryostat is a device used to maintain low cryogenic temperatures of samples or devices mounted within the cryostat. [2.25]


  • D-Wave: D-Wave Systems, Inc. is a quantum computing company, based in Burnaby, British Columbia, Canada. [4.23], [4.24], [4.25]
  • decoherence: Quantum decoherence is the degradation of a state over time, reducing the fidelity (quality) of a system, leading to errors in quantum computation. [2.1], [2.14], [2.17], [2.28], [4.2], [4.4], [4.9], [4.12], [4.27]
  • Defense Advanced Research Projects Agency : DARPA (Defense Advanced Research Projects Agency) is the independent research branch of the U.S. Department of Defense that funded a project (ARPANET) that in time was to lead to the creation of the Internet. [4.22]
  • Deutsch-Jozsa algorithm: The Deutsch-Jozsa algorithm can determine whether a function mapping all bitstrings to a single bit is constant or balanced, provided that it is one of the two. [1.10]
  • Deutsch, David: Physicist at the University of Oxford. [1.5], [2.8], [4.2], [4.23], [4.28], [4.29]
  • Dirac’s ket notation: Bra–ket notation, developed by Paul Dirac, is a standard notation for describing quantum states. [2.8]
  • dopant atoms : A dopant, also called a doping agent, is a trace impurity element that is inserted into a substance (in very low concentrations) to alter the electrical or optical properties of the substance. [1.4]


  • Einstein, Albert: Theoretical physicist.Einstein developed the theory of relativity, one of the two pillars of modern physics (alongside quantum mechanics). 1.1, [1.5], [2.10], [2.23]
  • Entropy: Entropy is a mathematical measure of the amount of disorder in a system, originally introduced to explain why part of a thermodynamic system’s total energy is unavailable to do useful work. [2.14]
  • Euler’s equation: Euler’s identity. Euler’s identity is an equality found in mathematics that has been compared to a Shakespearean sonnet and described as “the most beautiful equation.” [2.3]


  • Feynman, Richard: American theoretical physicist, Nobel Prize winner, Caltech professor, safecracker, drummer, and author of “There’s Plenty of Room at the Bottom” (commonly cited as the inspiration for nanotechnology) and one of the first to suggest the idea of quantum computation. [1.2], [1.5], [1.9], [2.14], [3.23], [4.28]


  • general number field sieve: In number theory, the general number field sieve (GNFS) is the most efficient classical algorithm known for factoring integers larger than 10^100. [3.6]
  • GPU (graphics processing unit) : A graphics processing unit (GPU) is a specialized electronic circuit designed to rapidly manipulate and alter memory to accelerate the creation of images in a frame buffer intended for output to a display device. [2.18]
  • GV: GV, formerly Google Ventures, is the venture capital investment arm of Alphabet Inc. [4.25]
  • Hadamard gate: The Hadamard gate is a 180 degree rotation around the diagonal X+Z axis of the Bloch sphere. [2.14], [2.15], [2.18], [2.22], [3.19], [3.23], [4.15]


  • Hamming distance: Hamming distance between two bit strings is the number of bits that would have to be changed to transform one string into the other. [4.12], [4.15]
  • Hamming Richard: American mathematician who invented important concepts in (classical) error correction, and for whom the Hamming distance is named. [4.12]
  • Haroche, Serge: French physicist who was awarded the 2012 Nobel Prize. [1.15], [4.29]
  • Hilbert space: The mathematical concept. A Hilbert space is an abstract vector space possessing the structure of an inner product that allows length and angle to be measured. [2.8]
  • Hilbert, David: German mathematician. [2.8]


  • IARPA: The Intelligence Advanced Research Projects Activity (IARPA) is an organization within the Office of the Director of National Intelligence responsible for leading research to overcome difficult challenges relevant to the United States Intelligence Community. [2.22], [4.22]
  • id Quantique: ID Quantique (IDQ) is a Swiss company based in Geneva, Switzerland, which provides quantum key distribution (QKD) systems, quantum safe network encryption, single photon counters, and hardware random number generators. [4.24]
  • Josephson junction: A Josephson junction is a tiny gap in a superconductor across which superconducting pairs of electrons can tunnel. [2.25], [4.7]


  • JSPS: The Japan Society for the Promotion of Science (JSPS) is Japan’s leading funding agency and is largely funded through annual subsidies from the Japanese Ministry of Education, Culture, Sports, Science and Technology. [4.22]


  • Lazaridis, Mike: Greek-Canadian businessman, investor in quantum computing technologies, and founder of BlackBerry. [4.22], [4.25], [4.28]


  • Machine Learning: Machine learning is the science of getting computers to act without being explicitly programmed. [1.10], [1.13], [1.20], [3.19], [4.27], [4.28]
  • MagiQ Technologies: MagiQ Technologies, Inc is an American technology development company headquartered in Somerville, Massachusetts. [4.24]
  • modulo arithmetic: Arithmetic keeping results between 0 and N-1 (inclusive) by subtracting N as necessary is said to be modulo N arithmetic. It corresponds to arithmetic done in base N and discarding all digits except the lowest-order digit. [3.6], [3.7], [3.8], [3.14], [4.27]
  • Moore’s Law: Moore’s law is the observation that the number of transistors in a dense integrated circuit doubles approximately every two years. Created by Gordon Moore, founder of Intel, it is an industrial economic imperative rather than a law of physics. [1.4], [3.18]


  • NEA: New Enterprise Associates, a Silicon Valley venture capital firm. [4.25]
  • NICT: National Institute of Information and Communications Technology (JAPAN) [4.22]
  • NII: National Institute of Informatics (JAPAN) [4.22]
  • no-cloning theorem: The no cloning theorem is a result of quantum mechanics which forbids the creation of identical copies of an arbitrary unknown quantum state. [2.1], [2.15], [2.16], [2.28], [4.22], [4.27]
  • Non-volatile Storage: computer memory that is able to hold saved data even if there is no power, and does not require periodic refreshes of its memory data. Hard disks and flash memory are both non-volatile storage. [1.13]
  • NSF: National Science Foundation (US) [4.22]



  • Ortigoso, Juan: Spanish quantum researcher. [2.15]
  • Oxford Instruments: Oxford Instruments leading provider of high technology tools and systems for research and industry. [4.24]


  • Podolsky, Boris: American physicist. [1.5]
  • probability amplitudes : The quantum probability amplitude is a complex number representing the size and phase of a particular basis vector in a quantum state. [2.3], [2.5], [2.6], [3.6]
  • pulses: A short period of energy that is repeated regularly, such as a short, loud sound or a short flash of light. [2.17], [4.6], [4.8], [4.9]


  • Quantum Valley: Quantum Valley Investments operates as a venture capital investment firm. [4.25]
  • Qubitekk: Qubitekk is the world’s first company dedicated to commercialize Quantum Entanglement Sources required to speed the adoption of quantum computing and cryptography technologies and applications. [4.24]
  • Quintessence Labs: Cyber Security Company. [4.24]


  • RAM: Random access memory. [2.18]
  • Raussendorf, Robert: physicist at University of British Columbia [4.15]
  • Research in Motion: Research in Motion, or RIM, is a Canadian multinational telecommunications company based in Waterloo, Ontario, Canada. [4.25]
  • reversible computing: Reversible computing is a model of computing where the computational process to some extent is reversible, i.e., time-invertible. Reversible computing reduces waste energy for classical systems, and is the logical description of the unitary evolution of quantum systems. [1.2], [2.14], [4.22]
  • Rigetti Computing: Rigetti Computing is a quantum computing company focusing on building a superconducting quantum computer. [2.22], [4.24]
  • Rigetti, Chad: Quantum computing physicist and the founder and CEO of Rigetti Computing. [2.22], [4.10], [4.24]
  • RIKEN: Institute of Physical and Chemical Research (JAPAN) [4.22]
  • Rosen, Nathan: American-Israeli physicist. [1.5]
  • RSA: Rivest, Shamir and Adelman. RSA can refer to either the company of the same name or the public-key cryptography scheme developed by the three researchers. [4.27]


  • Schrodinger’s equation: In quantum mechanics, the Schrödinger equation is a mathematical equation that describes the changes over time of a physical system in which quantum effects, such as wave–particle duality, are significant. [2.2]
  • SeQureNet: SeQureNet is a start-up company in Paris. [4.24]
  • Shor, Peter: Peter Williston Shor (born August 14, 1959) is an American professor of applied mathematics at MIT. [1.2], [1.10], [1.11], [2.9], [2.18], [3.1], [3.5], [3.6], [3.14], [3.16], [3.17], [4.2], [4.10], [4.12], [4.15], [4.22], [4.23], [4.24], [4.27], [4.28]
  • Steane, Andrew: Andrew Steane, professor at University of Oxford with expertise in Quantum Physics. [2.22], [4.15], [4.28]
  • supercomputer: A supercomputer is a computer with a high level of computing performance compared to a general-purpose computer. [1.11], [1.13], [4.2]
  • superconducting devices: Superconducting devices are electronic devices that harness the zero-resistance properties of superconductors. Electrical current in a superconductor can flow forever, with no dissipation. [4.15]
  • superconducting qubit : Superconducting qubits are electronic circuits comprising lithographically defined Josephson tunnel junctions, inductors, capacitors, and interconnects. [2.17], [4.7], [4.9], [4.24]
  • superpolynomial time: Superpolynomial execution time cannot be bounded by any fixed polynomial. Some such functions are intermediate between polynomial and exponential, for example, [1.10], [1.11], [3.1]


  • time domain multiplexing: Time-division multiplexing (TDM) is a method of transmitting and receiving independent signals over a common signal path by means of synchronized switches at each end of the transmission line so that each signal appears on the line only a fraction of time in an alternating pattern. [4.5]



  • Volatile Storage: Volatile storage is a type of computer memory that needs power to preserve stored data. RAM is volatile storage. [1.13]


  • wave function : The quantum wave function is the state of a quantum mechanical system, and can be written down using the state vector in ket notation. [2.5], [3.4]
  • Wineland, David: American Nobel-laureate physicist at the National Institute of Standards and Technology (NIST) physics laboratory. [1.5], [4.29]


  • XOR (exclusive OR) : Exclusive Or (XOR) is a logical operation that outputs true only when inputs differ (one is true, the other is false). [2.14], [4.14]



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