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W State
The W state is an quantum entanglement, entangled quantum state of three qubits which in the bra-ket notation has the following shape : , \mathrm\rangle = \frac(, 001\rangle + , 010\rangle + , 100\rangle) and which is remarkable for representing a specific type of multipartite entanglement and for occurring in several applications in quantum information theory. Particles prepared in this state reproduce the properties of Bell's theorem, which states that no classical theory of local hidden variables can produce the predictions of quantum mechanics. The state is named after Wolfgang Dür, Wolfgang Dür, who first reported the state together with Guifré Vidal, and Juan Ignacio Cirac Sasturain, Ignacio Cirac in 2000. Properties The W state is the representative of one of the two non-biseparable classes of three-qubit states, the other being the Greenberger–Horne–Zeilinger state, , \mathrm\rangle = (, 000\rangle + , 111\rangle)/\sqrt. The , \mathrm\rangle and , \mathrm\rangle ... [...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] |
Juan Ignacio Cirac Sasturain
Juan Ignacio Cirac Sasturain (born 11 October 1965), known professionally as Ignacio Cirac, is a Spanish physicist. He is one of the pioneers of the field of quantum computing and quantum information theory. He was awarded the 2013 Wolf Prize in Physics. Early life and education Juan Ignacio Cirac Sasturain graduated from the Complutense University of Madrid in 1988. Career Cirac moved to the United States in 1991 to work as a postdoctoral scientist with Peter Zoller in the Joint Institute for Laboratory Astrophysics in University of Colorado at Boulder. Between 1991 and 1996, he was teaching physics in the Ciudad Real Faculty of Chemistry, University of Castilla-La Mancha. In 1996, Cirac became professor in the Institut für Theoretische Physik in Innsbruck, Austria, and in 2001 he became a director of the Max Planck Institute of Quantum Optics in Garching, Germany, where he heads the Theory Division. At the same time, he was appointed honorary professor at t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
NOON State
In quantum optics, a NOON state or N00N state is a quantum-mechanical many-body entangled state: : , \text \rangle = \frac, \, which represents a superposition of ''N'' particles in mode ''a'' with zero particles in mode ''b'', and vice versa. Usually, the particles are photons, but in principle any bosonic field can support NOON states. Applications NOON states are an important concept in quantum metrology and quantum sensing for their ability to make precision phase measurements when used in an optical interferometer. For example, consider the observable : A = , N,0\rangle\langle 0,N, + , 0,N\rangle\langle N,0, . \, The expectation value of A for a system in a NOON state switches between +1 and −1 when \theta changes from 0 to \pi/N. Moreover, the error in the phase measurement becomes : \Delta \theta = \frac = \frac. This is the so-called Heisenberg limit, and gives a quadratic improvement over the standard quantum limit. NOON states are closely rel ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Multipartite Entanglement
In the case of systems composed of m > 2 subsystems, the classification of quantum-entangled states is richer than in the bipartite case. Indeed, in multipartite entanglement apart from fully separable states and fully entangled states, there also exists the notion of partially separable states. Full and partial separability The definitions of fully separable and fully entangled multipartite states naturally generalizes that of separable and entangled states in the bipartite case, as follows. Full ''m''-partite separability (''m''-separability) of ''m'' systems The state \; \varrho_ of \; m subsystems \; A_1, \ldots, A_m with Hilbert space \; \mathcal_=\mathcal_\otimes\ldots\otimes \mathcal_ is fully separable if and only if it can be written in the form :\; \varrho_ = \sum_^k p_i \varrho_^i \otimes \ldots \otimes \varrho_^i. Correspondingly, the state \; \varrho_ is fully entangled if it cannot be written in the above form. As in the bipartite case, the set of \; m-sep ... [...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] |
Greenberger–Horne–Zeilinger State
In physics, in the area of quantum information theory, a Greenberger–Horne–Zeilinger (GHZ) state is an entangled quantum state that involves at least three subsystems (particle states, qubits, or qudits). Named for the three authors that first described this state, the GHZ state predicts outcomes from experiments that directly contradict predictions by every classical local hidden-variable theory. The state has applications in quantum computing. History The four-particle version was first studied by Daniel Greenberger, Michael Horne and Anton Zeilinger in 1989. The following year Abner Shimony joined in and they published a three-particle version based on suggestions by N. David Mermin. Experimental measurements on such states contradict intuitive notions of locality and causality. GHZ states for large numbers of qubits are theorized to give enhanced performance for metrology compared to other qubit superposition states. Definition The GHZ state is an entangled q ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Product State
In quantum mechanics, separable states are multipartite quantum states that can be written as a convex combination of product states. Product states are multipartite quantum states that can be written as a tensor product of states in each space. The physical intuition behind these definitions is that product states have no correlation between the different degrees of freedom, while separable states might have correlations, but all such correlations can be explained as due to a classical random variable, as opposed to being due to entanglement. In the special case of pure states the definition simplifies: a pure state is separable if and only if it is a product state. A state is said to be entangled if it is not separable. In general, determining if a state is separable is not straightforward and the problem is classed as NP-hard. Separability of bipartite systems Consider first composite states with two degrees of freedom, referred to as ''bipartite states''. By a postulat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Guifré Vidal
Guifré Vidal is a Spanish physicist who is working on quantum many-body physics using analytical and numerical techniques. In particular, he is one of the leading experts of tensor network state implementations such as time-evolving block decimation (TEBD) and multiscale entanglement renormalization ansatz (MERA). He was previously a faculty member of Perimeter Institute in Waterloo, Canada. However as of September 2019, he is now a research scientist at Sandbox @ Alphabet. External linksScience Watch interview {{DEFAULTSORT:Vidal, Guifre Spanish physicists Living people [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Quantum State
In quantum physics, a quantum state is a mathematical entity that embodies the knowledge of a quantum system. Quantum mechanics specifies the construction, evolution, and measurement of a quantum state. The result is a prediction for the system represented by the state. Knowledge of the quantum state, and the rules for the system's evolution in time, exhausts all that can be known about a quantum system. Quantum states may be defined differently for different kinds of systems or problems. Two broad categories are * wave functions describing quantum systems using position or momentum variables and * the more abstract vector quantum states. Historical, educational, and application-focused problems typically feature wave functions; modern professional physics uses the abstract vector states. In both categories, quantum states divide into pure versus mixed states, or into coherent states and incoherent states. Categories with special properties include stationary states for tim ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wolfgang Dür
Wolfgang Dür (born 25 October 1973) is an Austrian theoretical physicist and conducts research in the field of quantum information theory and quantum communication. He is a full professor at the University of Innsbruck, Austria. Biography Dür studied physics at the University of Innsbruck and earned his doctorate sub auspiciis praesidentis in 2001 under the supervision of Ignacio Cirac. Following his PhD, he pursued postdoctoral research at the University of Munich before returning to Innsbruck, where he earned his habilitation in 2008. He became full professor in 2023. He also studied physics and mathematics to become a high school teacher. He is married and has two children. Research and career Wolfgang Dür work focuses on topics such as quantum networks, quantum metrology, and measurement-based quantum computation. Dür is well-known for his contributions to the development of quantum repeaters, a key concept for enabling quantum communication over long d ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bell's Theorem
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 mec ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
