53,111 research outputs found
Quantum Mechanics and Stochastic Mechanics for compatible observables at different times
Bohm Mechanics and Nelson Stochastic Mechanics are confronted with Quantum
Mechanics in presence of non-interacting subsystems. In both cases, it is shown
that correlations at different times of compatible position observables on
stationary states agree with Quantum Mechanics only in the case of product wave
functions. By appropriate Bell-like inequalities it is shown that no classical
theory, in particular no stochastic process, can reproduce the quantum
mechanical correlations of position variables of non interacting systems at
different times.Comment: Plain Te
The State Space of Perturbative Quantum Field Theory in Curved Spacetimes
The space of continuous states of perturbative interacting quantum field
theories in globally hyperbolic curved spacetimes is determined. Following
Brunetti and Fredenhagen, we first define an abstract algebra of observables
which contains the Wick-polynomials of the free field as well as their
time-ordered products, and hence, by the well-known rules of perturbative
quantum field theory, also the observables (up to finite order) of interest for
the interacting quantum field theory. We then determine the space of continuous
states on this algebra. Our result is that this space consists precisely of
those states whose truncated n-point functions of the free field are smooth for
all n not equal to two, and whose two-point function has the singularity of a
Hadamard fundamental form. A crucial role in our analysis is played by the
positivity property of states. On the technical side, our proof involves
functional analytic methods, in particular the methods of microlocal analysis.Comment: 24 pages, Latex file, no figure
Large deviations in quantum lattice systems: one-phase region
We give large deviation upper bounds, and discuss lower bounds, for the
Gibbs-KMS state of a system of quantum spins or an interacting Fermi gas on the
lattice. We cover general interactions and general observables, both in the
high temperature regime and in dimension one.Comment: 30 pages, LaTeX 2
The Schr\" odinger picture of the Dirac quantum mechanics on spatially flat Robertson-Walker backgrounds
The Schr\" odinger picture of the Dirac quantum mechanics is defined in
charts with spatially flat Robertson-Walker metrics and Cartesian coordinates.
The main observables of this picture are identified, including the interacting
part of the Hamiltonian operator produced by the minimal coupling with the
gravitational field. It is shown that in this approach new Dirac quantum modes
on de Sitter spacetimes may be found analytically solving the Dirac equation.Comment: 6 pages 0 figure
Simulating Physical Phenomena by Quantum Networks
Physical systems, characterized by an ensemble of interacting elementary
constituents, can be represented and studied by different algebras of
observables or operators. For example, a fully polarized electronic system can
be investigated by means of the algebra generated by the usual fermionic
creation and annihilation operators, or by using the algebra of Pauli
(spin-1/2) operators. The correspondence between the two algebras is given by
the Jordan-Wigner isomorphism. As we previously noted similar one-to-one
mappings enable one to represent any physical system in a quantum computer. In
this paper we evolve and exploit this fundamental concept in quantum
information processing to simulate generic physical phenomena by quantum
networks. We give quantum circuits useful for the efficient evaluation of the
physical properties (e.g, spectrum of observables or relevant correlation
functions) of an arbitrary system with Hamiltonian .Comment: 44 pages, 15 psfigur
Scaling behavior in the adiabatic Dicke Model
We analyze the quantum phase transition for a set of -two level systems
interacting with a bosonic mode in the adiabatic regime. Through the
Born-Oppenheimer approximation, we obtain the finite-size scaling expansion for
many physical observables and, in particular, for the entanglement content of
the system.Comment: 4 pages, 3 figure
Dissipative Entanglement of Quantum Spin Fluctuations
We consider two non-interacting infinite quantum spin chains immersed in a
common thermal environment and undergoing a local dissipative dynamics of
Lindblad type. We study the time evolution of collective mesoscopic quantum
spin fluctuations that, unlike macroscopic mean-field observables, retain a
quantum character in the thermodynamical limit. We show that the microscopic
dissipative dynamics is able to entangle these mesoscopic degrees of freedom,
through a purely mixing mechanism. Further, the behaviour of the dissipatively
generated quantum correlations between the two chains is studied as a function
of temperature and dissipation strength.Comment: 54 pages, 8 figure
Resummation for Nonequilibrium Perturbation Theory and Application to Open Quantum Lattices
Lattice models of fermions, bosons, and spins have long served to elucidate
the essential physics of quantum phase transitions in a variety of systems.
Generalizing such models to incorporate driving and dissipation has opened new
vistas to investigate nonequilibrium phenomena and dissipative phase
transitions in interacting many-body systems. We present a framework for the
treatment of such open quantum lattices based on a resummation scheme for the
Lindblad perturbation series. Employing a convenient diagrammatic
representation, we utilize this method to obtain relevant observables for the
open Jaynes-Cummings lattice, a model of special interest for open-system
quantum simulation. We demonstrate that the resummation framework allows us to
reliably predict observables for both finite and infinite Jaynes-Cummings
lattices with different lattice geometries. The resummation of the Lindblad
perturbation series can thus serve as a valuable tool in validating open
quantum simulators, such as circuit-QED lattices, currently being investigated
experimentally.Comment: 15 pages, 9 figure
Dynamics of a quantum oscillator strongly and off-resonantly coupled with a two-level system
Beyond the rotating-wave approximation, the dynamics of a quantum oscillator
interacting strongly and off-resonantly with a two-level system exhibit
beatings, whose period equals the revival time of the two-level system. On a
longer time scale, the quantum oscillator shows collapses, revivals and
fractional revivals, which are encountered in oscillator observables like the
mean number of oscillator quanta and in the two-level inversion population.
Also the scattered oscillator field shows doublets with symmetrically displaced
peaks.Comment: 19 pages, 5 figure
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