1,721,211 research outputs found
History operators in quantum mechanics
No full textIt is convenient to describe a quantum system at all times by means of a "history operator" C, encoding measurements and unitary time evolution between measurements. These operators naturally arise when computing the probability of measurement sequences, and generalize the "sum over position histories" of the Feynman path-integral. As we argue in this work, this description has some computational advantages over the usual state vector description, and may help to clarify some issues regarding nonlocality of quantum correlations and collapse. A measurement on a system described by C modifies the history operator, C→PC, where P is the projector corresponding to the measurement. We refer to this modification as "history operator collapse". Thus, C keeps track of the succession of measurements on a system, and contains all histories compatible with the results of these measurements. The collapse modifies the history content of C, and therefore modifies also the past (relative to the measurement), but never in a way to violate causality. Probabilities of outcomes are obtained as Tr(C†PC)/Tr(C†C). A similar formula yields probabilities for intermediate measurements, and reproduces the result of the two-vector formalism in the case of the given initial and final states. We apply the history operator formalism to a few examples: entangler circuit, Mach-Zehnder interferometer, teleportation circuit and three-box experiment. Not surprisingly, the propagation of coordinate eigenstates |q) is described by a history operator C containing the Feynman path-integral
Entropy of temporal entanglement
Full text linkA recently proposed history formalism is used to define temporal entanglement in quantum systems, and compute its entropy. The procedure is based on the time-reduction of the history density operator, and allows a symmetrical treatment of space and time correlations. Temporal entanglement entropy is explicitly calculated in two simple quantum computation circuits
Covariant hamiltonian for supergravity in d = 3 and d = 4
No full textWe extend the covariant canonical formalism recently discussed in ref. [1] to geometric theories coupled to both bosonic and fermionic p-forms. This allows a covariant hamiltonian treatment of supergravity theories. As examples we present the covariant hamiltonian formulation for d = 3 anti-De Sitter supergravity and for the “new minimal” d = 4, N = 1 supergravity (with 1-form and 2-form auxiliary fields). Form-Poisson brackets and form-Dirac brackets are defined, and used to find the form-canonical generators of all gauge symmetries via an algorithmic procedure
Twisted Chern‐Simons supergravity
No full textWe present a noncommutative version of D = 5 Chern-Simons supergravity, where noncommutativity is en- coded in a ⋆-product associated to an abelian Drinfeld twist. The theory is invariant under diffeomorphisms, and under the ⋆-gauge supergroup SU(2,2|4), including Lorentz and N = 4 local supersymmetries
Space and Time Correlations in Quantum Histories
No full textThe formalism of generalized quantum histories allows a symmetrical treatment of space and time correlations, by taking different traces of the same history density matrix. In this framework, the characterization of spatial and temporal entanglement is revisited. An operative protocol is presented, to map a history state into the ket of a static composite system. It is demonstrated, by examples, how the Leggett-Garg and the temporal Clauser-Horne-Shimony-Holt (CHSH) inequalities can be violated in this approach
All quantum mixtures are proper
Full text linkIt is argued that proper and improper quantum mixed states have no observable differences, and hence should not be distinguished. This has implications for subjective approaches to quantum mechanics, and invalidates one of the main motivations for relational interpretations of QM
BRANE NEW WORLD AND NONCOMMUTATIVE GEOMETRY. PROCEEDINGS, EUROCONFERENCE, Mod. Phys. Lett. A16 (2001) 163-402
No full textEuroconferenc
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