1,230 research outputs found
Dynamical invariants and nonadiabatic geometric phases in open quantum systems
We introduce an operational framework to analyze non-adiabatic Abelian and
non-Abelian, cyclic and non-cyclic, geometric phases in open quantum systems.
In order to remove the adiabaticity condition, we generalize the theory of
dynamical invariants to the context of open systems evolving under arbitrary
convolutionless master equations. Geometric phases are then defined through the
Jordan canonical form of the dynamical invariant associated with the
super-operator that governs the master equation. As a by-product, we provide a
sufficient condition for the robustness of the phase against a given decohering
process. We illustrate our results by considering a two-level system in a
Markovian interaction with the environment, where we show that the
non-adiabatic geometric phase acquired by the system can be constructed in such
a way that it is robust against both dephasing and spontaneous emission.Comment: 9 pages, 3 figures. v2: minor corrections and subsection IV.D added.
Published versio
An exact master equation for the system-reservoir dynamics under the strong coupling regime and non-Markovian dynamics
In this paper we present a method to derive an exact master equation for a
bosonic system coupled to a set of other bosonic systems, which plays the role
of the reservoir, under the strong coupling regime, i.e., without resorting to
either the rotating-wave or secular approximations. Working with phase-space
distribution functions, we verify that the dynamics are separated in the
evolution of its center, which follows classical mechanics, and its shape,
which becomes distorted. This is the generalization of a result by Glauber, who
stated that coherent states remain coherent under certain circumstances,
specifically when the rotating-wave approximation and a zero-temperature
reservoir are used. We show that the counter-rotating terms generate
fluctuations that distort the vacuum state, much the same as thermal
fluctuations.Finally, we discuss conditions for non-Markovian dynamics
Control of the geometric phase and pseudo-spin dynamics on coupled Bose-Einstein condensates
We describe the behavior of two coupled Bose-Einstein condensates in
time-dependent (TD) trap potentials and TD Rabi (or tunneling) frequency, using
the two-mode approach. Starting from Bloch states, we succeed to get analytical
solutions for the TD Schroedinger equation and present a detailed analysis of
the relative and geometric phases acquired by the wave function of the
condensates, as well as their population imbalance. We also establish a
connection between the geometric phases and constants of motion which
characterize the dynamic of the system. Besides analyzing the affects of
temporality on condensates that differs by hyperfine degrees of freedom
(internal Josephson effect), we also do present a brief discussion of a one
specie condensate in a double-well potential
(external Josephson effect).Comment: 1 tex file and 11 figures in pdf forma
Teleportation of a Zero-and One-photon Running Wave State by Projection Synthesis
We show how to teleport a running wave superposition of zero- and one-photon
field state through the projection synthesis technique. The fidelity of the
scheme is computed taking into account the noise introduced by dissipation and
the efficiency of the detectors. These error sources have been introduced
through a single general relationship between input and output operators.Comment: 11 pages, 1 figur
Nonadiabatic coherent evolution of two-level systems under spontaneous decay
In this paper we extend current perspectives in engineering reservoirs by
producing a time-dependent master equation leading to a nonstationary
superposition equilibrium state that can be nonadiabatically controlled by the
system-reservoir parameters. Working with an ion trapped inside a nonindeal
cavity we first engineer effective Hamiltonians that couple the electronic
states of the ion with the cavity mode. Subsequently, two classes of
decoherence-free evolution of the superposition of the ground and decaying
excited levels are achieved: those with time-dependent azimuthal or polar
angle. As an application, we generalise the purpose of an earlier study [Phys.
Rev. Lett. 96, 150403 (2006)], showing how to observe the geometric phases
acquired by the protected nonstationary states even under a nonadiabatic
evolution.Comment: 5 pages, no figure
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