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Quantum
A quantum (plural: quanta) is the smallest discrete unit of a physical quantity, introduced by Max Planck in 1900; quantum mechanics underlies lasers, transistors, and GPS.
Quantum acoustics
Quantum acoustics is the field studying interactions between matter and sound at the quantum level, with the phonon as its quantum of excitation, analogous to quantum optics.
Quantum affine algebra
A quantum affine algebra, or affine quantum group, is a Hopf algebra that q-deforms the enveloping algebra of an affine Kac–Moody algebra, introduced by Drinfeld and Jimbo around 1985.
Quantum algorithm
A quantum algorithm is a step-by-step procedure executed on a quantum computer, in which qubits carry information in superposition; Shor's 1994 factoring and Grover's 1996 search are the landmark examples.
Quantum algorithms for differential equations
Quantum algorithms for differential equations solve linear ordinary and partial differential equations by reducing them to sparse linear systems for quantum solvers such as HHL and QSVT.
Quantum annealing
Quantum annealing is a heuristic optimization method using quantum fluctuations to find low-energy states of an objective function, introduced by Kadowaki and Nishimori in 1998.
Quantum anomalous Hall effect
The quantum anomalous Hall effect is a quantized Hall effect occurring without an external magnetic field, first observed in magnetically doped topological insulators in 2013.
Quantum approximate optimization algorithm
The quantum approximate optimization algorithm (QAOA) is a hybrid quantum-classical algorithm for combinatorial optimization problems like Max-Cut, proposed by Farhi, Goldstone, and Gutmann in 2014.
Quantum backaction-evading measurement
A quantum backaction-evading (BAE) measurement is a quantum nondemolition scheme measuring only one quadrature of an oscillator's motion, so detector backaction diverts to the unmeasured quadrature.
Quantum battery
A quantum battery is a microscopic quantum system that stores energy and delivers it as work, a concept introduced by Robert Alicki and Mark Fannes in 2013.
Quantum Bayesianism
Quantum Bayesianism, or QBism, is an interpretation of quantum mechanics, founded by Caves, Fuchs, and Schack in 2002, in which a quantum state expresses an agent's personal beliefs.
Quantum beat spectroscopy
Quantum beat spectroscopy is a Doppler-free laser technique that measures small energy splittings in atoms and molecules, reading beat frequencies in fluorescence after pulsed excitation.
Quantum bouncer
The quantum bouncer is the quantum system of a particle in a uniform gravitational field above a reflecting mirror; ultracold neutrons showed its discrete bound states in 2002.
Quantum capacitance
Quantum capacitance is the capacitance contribution arising from a finite density of electronic states, introduced in 1988; it limits capacitance in graphene and other low-dimensional electrodes.
Quantum capacity
Quantum capacity, also called quantum channel capacity, is the maximum rate in qubits per channel use at which quantum information can be transmitted reliably through a noisy quantum channel.
Quantum cascade laser
A quantum cascade laser (QCL) is a unipolar semiconductor laser, first demonstrated at Bell Laboratories in 1994, whose wavelength is set by quantum well thickness and used for gas sensing and spectroscopy.
Quantum cascade laser infrared imaging
Quantum cascade laser infrared imaging is a chemical imaging technique in which a mid-infrared quantum cascade laser maps a sample's chemical composition, chiefly for label-free digital pathology of unstained tissue.
Quantum cascade laser infrared spectroscopy
Quantum cascade laser infrared spectroscopy, or QCL-IR spectroscopy, is a family of mid-infrared analysis techniques using a quantum cascade laser source, first demonstrated at Bell Laboratories in 1994.
Quantum cellular automaton
A quantum cellular automaton (QCA) is an array of quantum systems on a lattice that evolves in discrete time steps by a translation-invariant, causal, unitary rule.
Quantum channel
A quantum channel, or quantum communication channel, is a completely positive, trace-preserving linear map on density matrices that describes any physical change of a quantum state, including gates, measurements, noise, and communication.
Quantum chaos
Quantum chaos is the field of physics that studies quantum fingerprints of classical chaos, identified indirectly through energy-level statistics, eigenfunctions, and dynamics, since quantum evolution is linear.
Quantum Cheshire cat
The quantum Cheshire cat is a proposed quantum effect in which a particle's property, such as spin, appears in a different place from the particle, proposed in 2013.
Quantum chromodynamics
Quantum chromodynamics (QCD) is the quantum field theory of the strong interaction that binds quarks and gluons into protons and neutrons; developed in the early 1970s, it generates most ordinary mass.
Quantum circuit
A quantum circuit, also called the circuit model of quantum computation, is a sequence of unitary gates, measurements, and classical control acting on qubits; ideal circuits are reversible.
Quantum circuit complexity
Quantum circuit complexity measures how large a quantum circuit must be to implement a given unitary or Boolean function, counting gates (size) and parallel layers (depth).
Quantum circuit transpilation
Quantum circuit transpilation is the compiler step that rewrites an abstract quantum circuit into one a specific device can execute, decomposing gates into native sets, assigning qubits, and inserting SWAPs.
Quantum Circuits
S. Harvey Moseley is an American astronomer and instrumentation physicist elected to the National Academy of Sciences in 2023, known for NASA's COBE, cryogenic X-ray detectors, and JWST microshutters.
Quantum clock synchronization
Quantum clock synchronization (QCS) is a set of protocols that establish a shared time reference between distant clocks using entanglement, single-photon interference, and other quantum correlations.
Quantum cloning
Quantum cloning is the approximate copying of unknown quantum states by a quantum cloning machine, since the no-cloning theorem forbids perfect replication; the best copies are measured by fidelity.
Quantum cohomology
Quantum cohomology is a deformation of the ordinary cohomology ring of a manifold in which the product counts holomorphic curves, introduced in the early 1990s from quantum string theory.