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Buscemi Nonlocality
Buscemi nonlocality, a concept proposed by Francesco Buscemi in 2012, refers to a type of quantum nonlocality that arises in Bell tests where the local measurement settings are determined not by classical programs but by quantum states. Such generalized tests are called ''semiquantum nonlocal games''. While, as the counterexample of Werner states shows, Bell nonlocality is known not to be equivalent to quantum entanglement Quantum entanglement is the phenomenon where the quantum state of each Subatomic particle, particle in a group cannot be described independently of the state of the others, even when the particles are separated by a large distance. The topic o ..., the latter instead turns out to be equivalent to Buscemi nonlocality: a quantum state is "Buscemi nonlocal" if and only if it is entangled. Semiquantum nonlocal tests constitute the basis for measurement device-independent entanglement witnesses and their feasibility has been experimentally verified several ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Quantum Nonlocality
In theoretical physics, quantum nonlocality refers to the phenomenon by which the measurement statistics of a multipartite quantum system do not allow an interpretation with local realism. Quantum nonlocality has been experimentally verified under a variety of physical assumptions. Quantum nonlocality does not allow for faster-than-light communication, and hence is compatible with special relativity and its universal speed limit of objects. Thus, quantum theory is local in the strict sense defined by special relativity and, as such, the term "quantum nonlocality" is sometimes considered a misnomer. Still, it prompts many of the foundational discussions concerning quantum theory. History Einstein, Podolsky and Rosen In the 1935 EPR paper, Albert Einstein, Boris Podolsky and Nathan Rosen described "two spatially separated particles which have both perfectly correlated positions and momenta" as a direct consequence of quantum theory. They intended to use the classical princip ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bell Test
A Bell test, also known as Bell inequality test or Bell experiment, is a real-world physics experiment designed to test the theory of quantum mechanics in relation to Albert Einstein's concept of local realism. Named for John Stewart Bell, the experiments test whether or not the real world satisfies local realism, which requires the presence of some additional local variables (called "hidden" because they are not a feature of quantum theory) to explain the behavior of particles like photons and electrons. The test empirically evaluates the implications of Bell's theorem. , all Bell tests have found that the hypothesis of local hidden variables is inconsistent with the way that physical systems behave. Many types of Bell tests have been performed in physics laboratories, often with the goal of ameliorating problems of experimental design or set-up that could in principle affect the validity of the findings of earlier Bell tests. This is known as "closing loopholes in Bell tests". ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Werner State
A Werner state is a -dimensional bipartite quantum state density matrix that is invariant under all unitary operators of the form U \otimes U. That is, it is a bipartite quantum state \rho_ that satisfies :\rho_ = (U \otimes U) \rho_ (U^\dagger \otimes U^\dagger) for all unitary operators ''U'' acting on ''d''-dimensional Hilbert space. These states were first developed by Reinhard F. Werner in 1989. General definition Every Werner state W_^ is a mixture of projectors onto the symmetric and antisymmetric subspaces, with the relative weight p \in ,1/math> being the main parameter that defines the state, in addition to the dimension d \geq 2: :W_^ = p \frac P^\text_ + (1-p) \frac P^\text_, where :P^\text_ = \frac(I_+F_), :P^\text_ = \frac(I_-F_), are the projectors and :F_ = \sum_ , i\rangle \langle j, _A \otimes , j\rangle \langle i, _B is the permutation or flip operator that exchanges the two subsystems ''A'' and ''B''. Werner states are separable for ''p'' ≥ and entang ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bell Nonlocality
Bell's theorem is a term encompassing a number of closely related results in physics, all of which determine that quantum mechanics is incompatible with local hidden-variable theories, given some basic assumptions about the nature of measurement. The first such result was introduced by John Stewart Bell in 1964, building upon the Einstein–Podolsky–Rosen paradox, which had called attention to the phenomenon of quantum entanglement. In the context of Bell's theorem, "local" refers to the principle of locality, the idea that a particle can only be influenced by its immediate surroundings, and that interactions mediated by physical fields cannot propagate faster than the speed of light. " Hidden variables" are supposed properties of quantum particles that are not included in quantum theory but nevertheless affect the outcome of experiments. In the words of Bell, "If hidden-variable theoryis local it will not agree with quantum mechanics, and if it agrees with quantum mechani ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Quantum Entanglement
Quantum entanglement is the phenomenon where the quantum state of each Subatomic particle, particle in a group cannot be described independently of the state of the others, even when the particles are separated by a large distance. The topic of quantum entanglement is at the heart of the disparity between classical physics and quantum physics: entanglement is a primary feature of quantum mechanics not present in classical mechanics. Measurement#Quantum mechanics, Measurements of physical properties such as position (vector), position, momentum, Spin (physics), spin, and polarization (waves), polarization performed on entangled particles can, in some cases, be found to be perfectly correlated. For example, if a pair of entangled particles is generated such that their total spin is known to be zero, and one particle is found to have clockwise spin on a first axis, then the spin of the other particle, measured on the same axis, is found to be anticlockwise. However, this behavior ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Entanglement Witness
In quantum information theory, an entanglement witness is a functional which distinguishes a specific entangled state from separable ones. Entanglement witnesses can be linear or nonlinear functionals of the density matrix. If linear, then they can also be viewed as observables for which the expectation value of the entangled state is strictly outside the range of possible expectation values of any separable state. Details Let a composite quantum system have state space H_A \otimes H_B. A mixed state ''ρ'' is then a trace-class positive operator on the state space which has trace 1. We can view the family of states as a subset of the real Banach space generated by the Hermitian trace-class operators, with the trace norm. A mixed state ''ρ'' is separable if it can be approximated, in the trace norm, by states of the form :\xi = \sum_ ^k p_i \, \rho_i^A \otimes \rho_i^B, where \rho_i^A and \rho_i^B are pure states on the subsystems ''A'' and ''B'' respectively. So th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
LOCC
LOCC, or local operations and classical communication, is a method in quantum information theory where a local (product) operation is performed on part of the system, and where the result of that operation is "communicated" classically to another part where usually another local operation is performed conditioned on the information received. Mathematical properties The formal definition of the set of LOCC operations is complicated due to the fact that later local operations depend in general on all the previous classical communication and due to the unbounded number of communication rounds. For any finite number r\geq1 one can define \operatorname_r, the set of LOCC operations that can be achieved with r rounds of classical communication. The set becomes strictly larger whenever r is increased and care has to be taken to define the limit of infinitely many rounds. In particular, the set LOCC is not topologically closed, that is there are quantum operations that can be approximat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
