All articles starting with Q
2,252 articles
Quantum spin liquid
A quantum spin liquid is a state of magnetic matter in which quantum fluctuations prevent spins from freezing into an ordered pattern, even at absolute zero.
Quantum spin liquid in α-RuCl3
α-RuCl3, or alpha ruthenium trichloride, is a layered honeycomb magnet regarded as the leading candidate to realize the Kitaev quantum spin liquid, where spins stay entangled even at zero temperature.
Quantum state
A quantum state is the mathematical description of a quantum system from which all measurement outcome probabilities can be computed, typically represented as vectors in a Hilbert space.
Quantum state merging
Quantum state merging is a quantum information theory protocol, introduced by Horodecki, Oppenheim, and Winter in 2005, transferring Alice's part of a shared unknown quantum state to Bob.
Quantum state space
Quantum state space is the set of all states a physical system can occupy, described mathematically as a complex Hilbert space and its density operators.
Quantum state tomography
Quantum state tomography is a set of measurement and estimation procedures that reconstructs the density matrix of a quantum system from repeated measurements on identical copies.
Quantum state transmission
Quantum state transmission is the transfer of an unknown quantum state from sender to receiver, either directly through a channel or by teleportation using shared entanglement and classical communication.
Quantum stochastic calculus
Quantum stochastic calculus is a noncommutative extension of Itô calculus, founded by Hudson and Parthasarathy in 1984, underlying quantum optics input-output theory, continuous measurement, and quantum filtering.
Quantum suicide and immortality
Quantum suicide and immortality, also called quantum immortality, is a thought experiment in which a quantum event triggers a lethal device, suggesting subjective survival under the many-worlds interpretation.
Quantum superabsorption
Quantum superabsorption is the cooperative enhancement of light absorption in quantum emitters, the time-reversed counterpart of Dicke superradiance, first demonstrated in 2021 with cold atoms.
Quantum superchemistry
Quantum superchemistry is a form of chemical reaction in a quantum degenerate gas, where atoms and molecules couple coherently as matter-wave fields, first observed in 2023.
Quantum superdiffusion
Quantum superdiffusion is anomalous quantum transport where spin or charge spreads faster than ordinary diffusion but slower than ballistic motion, seen most clearly in Heisenberg spin chains.
Quantum superposition
Quantum superposition, also known as superposition of states or quantum linear superposition, is the principle that a physical system can exist in a combination of two states, producing interference.
Quantum support vector machine
A quantum support vector machine (QSVM) is a quantum-computing version of the support vector machine, a supervised learning model, with part of training or prediction run on a quantum processor.
Quantum supremacy
Quantum supremacy, also called quantum advantage, is when a quantum computer performs a task no classical computer can in feasible time, a term coined in 2012.
Quantum Surgical
Quantum Surgical is a French medical robotics company founded in 2017 in Montpellier by Bertin Nahum, known for the Epione robotic-assisted platform for percutaneous tumor ablation.
Quantum switch
The quantum switch is a quantum process in which two operations act in a superposition of their two possible orders, with no definite causal order between them.
Quantum Systems (drone manufacturer)
Quantum Systems, also known as Quantum-Systems GmbH, is a German drone manufacturer founded by Florian Seibel in 2015, producing the Trinity survey drone and Vector reconnaissance drone.
Quantum Systems Vector
The Quantum Systems Vector is a battery-powered tail-sitter eVTOL fixed-wing drone built by Quantum-Systems GmbH of Gilching near Munich for military intelligence, surveillance, and reconnaissance missions, first delivered to Ukraine in 2022.
Quantum teleportation
Quantum teleportation is a protocol that transfers an unknown quantum state to a distant receiver using shared entanglement and two classical bits, proposed in 1993 and first demonstrated in 1997.
Quantum theory of atoms in molecules
The quantum theory of atoms in molecules (QTAIM) is a quantum chemistry method, developed by Richard Bader, that analyzes electron density to characterize bonding, atomic properties, and molecular structure.
Quantum thermodynamics
Quantum thermodynamics extends thermodynamics to systems small enough that fluctuations, coherence, and correlations matter, redefining work and heat and asking whether quantum effects improve heat engines.
Quantum thermometry
Quantum thermometry is the measurement of temperature using quantum probes like mesoscopic circuits and diamond NV centers, together with the theory of the precision limits such thermometers can reach.
Quantum trace
The quantum trace is a categorical generalization of the trace of a linear map, defined in ribbon categories and used to build knot invariants from braid representations.
Quantum trajectory theory
Quantum trajectory theory describes how a continuously measured open quantum system follows a random state path, whose average recovers the Lindblad master equation; introduced in the early 1990s.
Quantum transducer
A quantum transducer is a device that converts quantum signals between microwave and optical photons while preserving their quantum state, enabling superconducting quantum computers to be networked over optical fiber.
Quantum transduction
Quantum transduction, also called quantum frequency conversion, coherently converts quantum states between carriers such as microwave and optical photons, and is key to linking superconducting quantum computers through fiber.
Quantum Trinity
Quantum Trinity is a family of fixed-wing vertical take-off and landing mapping drones made by Quantum Systems, a Munich-based company, on the market since 2018.
Quantum tunnelling
Quantum tunnelling, also called barrier penetration, is the quantum-mechanical phenomenon in which a particle passes through an energy barrier that classical mechanics forbids, explained by the wavefunction's exponential decay.
Quantum tunnelling regime of plasmonics
The quantum tunnelling regime of plasmonics covers metal nanogaps below about one nanometre, where electrons tunnel between the metals and replace red-shifting gap plasmons with blue-shifting charge-transfer plasmons.