80 articles
Greenberger–Horne–Zeilinger state
The Greenberger–Horne–Zeilinger state (GHZ state) is a maximally entangled quantum state of three or more qubits whose perfect correlations conflict with local realism, shown in 1989.
Holevo's theorem
Holevo's theorem, also called the Holevo bound, is a result in quantum information theory proved by Alexander S. Holevo in 1973 that limits how much classical information measurements can extract.
Kraus operators
Kraus operators are matrices expressing a quantum operation as a weighted sum of conjugations, a form a map admits exactly when it is completely positive, introduced by Kraus in 1971.
LOCC
LOCC, or local operations and classical communication, is the class of operations in quantum information theory where separated parties act locally and exchange classical messages.
Logarithmic negativity
Logarithmic negativity is an entanglement measure for bipartite quantum states, introduced by Vidal and Werner in 2002, computable exactly for any mixed state and upper bounding distillable entanglement.
Logical qubit
A logical qubit is an encoded qubit protected by quantum error correction, formed from multiple physical qubits so that quantum information survives errors in any of its components.
Majorization
Majorization is a partial order on real vectors, introduced by Hardy, Littlewood, and Pólya, that formalizes one vector being more spread out, or less random, than another.
Majorization and entropy ordering of quantum states
Majorization is a preorder on probability vectors and quantum state spectra that formalizes when one distribution is more disordered, and by Nielsen's theorem it fully determines LOCC conversion of bipartite pure states.
Measurement-induced phase transition
A measurement-induced phase transition (MIPT) is a nonequilibrium phase transition in monitored quantum many-body systems, identified in random quantum circuits starting in 2018 and 2019.
Multi-user quantum capacity
Multi-user quantum capacity describes reliable information transmission through a quantum channel shared by several senders or receivers, where capacity becomes a set of achievable rate tuples.
Negativity (quantum entanglement)
Negativity is an entanglement measure for bipartite quantum states, introduced by G. Vidal and R. F. Werner in 2002 as a computable quantification of the Peres positive-partial-transpose criterion.
Noisy-channel coding theorem
The noisy-channel coding theorem, proved by Claude Shannon in 1948, states that data can be transmitted with arbitrarily few errors at any rate below a channel's capacity, but not above it.
Operational interpretations of quantum entropies
Operational interpretations of quantum entropies identify which quantum entropy answers which physical task: conditional entropy prices state merging, min- and max-entropies govern guessing and decoupling.
Out-of-time-order correlator
The out-of-time-order correlator, or OTOC, is a four-point quantum correlation function that tracks how a localized perturbation scrambles through a many-body system, serving as a diagnostic of quantum chaos.
Peres–Horodecki criterion
The Peres–Horodecki criterion, also called the positive partial transpose (PPT) criterion, is an entanglement test for bipartite quantum states, proposed by Asher Peres in 1996 and proven by the Horodeckis.
Private capacity of a quantum channel
The private capacity of a quantum channel is the maximum rate, in private bits per use, at which it transmits classical information an eavesdropper cannot learn.
Pseudorandom quantum states
Pseudorandom quantum states, or PRSs, are keyed quantum states generated efficiently by a quantum computer yet indistinguishable from Haar-random states by any efficient quantum adversary.
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 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 conditional entropy
Quantum conditional entropy, H(A|B) = H(AB) − H(B), measures the entropy of one part of a quantum system given the other, and can be negative when the parts are entangled.
Quantum data locking
Quantum data locking (QDL) is a quantum communication phenomenon in which a short secret key can encrypt an arbitrarily long quantum-encoded message, defying classical key-length requirements.
Quantum depolarizing channel
The quantum depolarizing channel is a noise model in quantum information theory where a state is kept with some probability and otherwise replaced by the maximally mixed state.
Quantum discord
Quantum discord is a measure of the quantumness of correlations in bipartite quantum systems, introduced by Ollivier and Zurek in 2001, which can be nonzero even without entanglement.
Quantum Fisher information as an entanglement witness
Quantum Fisher information as an entanglement witness is a diagnostic in which the quantum Fisher information, a quantity from quantum metrology, certifies multipartite entanglement in quantum many-body systems.
Quantum hypothesis testing
Quantum hypothesis testing is the task of deciding which of several candidate quantum states best describes a system, the quantum generalization of classical hypothesis testing.
Quantum information
Quantum information, also known as the quantum theory of information, is information encoded in quantum states like photon polarization and electron spin, whose basic unit is the qubit.
Quantum Information Theory (book)
Quantum Information Theory is a graduate textbook by Mark M. Wilde, published by Cambridge University Press in 2013 with a second edition in 2017, covering quantum Shannon theory.
Quantum low-density parity-check code
A quantum low-density parity-check (qLDPC) code is a quantum stabilizer code with sparse checks, allowing fault-tolerant computing with fewer physical qubits than the surface code.
Quantum mutual information
Quantum mutual information measures the total correlations, classical and quantum, shared between two parts of a quantum system, generalizing classical mutual information using von Neumann entropy.
Quantum relative entropy
The quantum relative entropy is a directed measure of distinguishability between two quantum states, defined as S(ρ||σ) = Tr ρ(log ρ − log σ), and is always non-negative.