133 research outputs found
Quantum theory of heating of a single trapped ion
The heating of trapped ions due to the interaction with a {\it quantized
environment} is studied {\it without performing the Born-Markov approximation}.
A generalized master equation local in time is derived and a novel theoretical
approach to solve it analytically is proposed. Our master equation is in the
Lindblad form with time dependent coefficients, thus allowing the simulation of
the dynamics by means of the Monte Carlo Wave Function (MCWF) method.Comment: 4 pages, 3 figure
Radiative collisional heating at the Doppler limit for laser-cooled magnesium atoms
We report Monte Carlo wave function simulation results on cold collisions
between magnesium atoms in a strong red-detuned laser field. This is the normal
situation e.g. in magneto-optical traps (MOT). The Doppler limit heating rate
due to radiative collisions is calculated for Mg-24 atoms in a magneto-optical
trap based on the singlet S_0 - singlet P_1 atomic laser cooling transition. We
find that radiative heating does not seem to affect the Doppler limit in this
case. We also describe a channelling mechanism due to the missing Q branch in
the excitation scheme, which could lead to a suppression of inelastic
collisions, and find that this mechanism is not present in our simulation
results due to the multistate character of the excitation process.Comment: 4 pages, RevTeX 4; v2 contains minor revisions based on referee
comments (5 pages
Misbelief and misunderstandings on the non--Markovian dynamics of a damped harmonic oscillator
We use the exact solution for the damped harmonic oscillator to discuss some
relevant aspects of its open dynamics often mislead or misunderstood. We
compare two different approximations both referred to as Rotating Wave
Approximation. Using a specific example, we clarify some issues related to
non--Markovian dynamics, non--Lindblad type dynamics, and positivity of the
density matrix.Comment: 6 pages, 2 figures, added info: submitted to J. Opt. B: Quantum and
Semiclass. Opt., Special Issue of the 10th Central European Workshop on
Quantum Optics, reference added, discussion clarifie
Initial correlations in open system's dynamics: The Jaynes-Cummings model
Employing the trace distance as a measure for the distinguishability of
quantum states, we study the influence of initial correlations on the dynamics
of open systems. We concentrate on the Jaynes-Cummings model for which the
knowledge of the exact joint dynamics of system and reservoir allows the
treatment of initial states with arbitrary correlations. As a measure for the
correlations in the initial state we consider the trace distance between the
system-environment state and the product of its marginal states. In particular,
we examine the correlations contained in the thermal equilibrium state for the
total system, analyze their dependence on the temperature and on the coupling
strength, and demonstrate their connection to the entanglement properties of
the eigenstates of the Hamiltonian. A detailed study of the time dependence of
the distinguishability of the open system states evolving from the thermal
equilibrium state and its corresponding uncorrelated product state shows that
the open system dynamically uncovers typical features of the initial
correlations.Comment: 12 pages, 7 figure
Sudden transition between classical and quantum decoherence
We study the dynamics of quantum and classical correlations in the presence
of nondissipative decoherence. We discover a class of initial states for which
the quantum correlations, quantified by the quantum discord, are not destroyed
by decoherence for times t < \bar{t}. In this initial time interval classical
correlations decay. For t > \bar{t}, on the other hand, classical correlations
do not change in time and only quantum correlations are lost due to the
interaction with the environment. Therefore, at the transition time \bar{t} the
open system dynamics exhibits a sudden transition from classical to quantum
decoherence regime.Comment: version accepted for publication by Physical Review Letter
Non-Markovian quantum jumps
Open quantum systems that interact with structured reservoirs exhibit
non-Markovian dynamics. We present a quantum jump method for treating the
dynamics of such systems. This approach is a generalization of the standard
Monte Carlo Wave Function (MCWF) method for Markovian dynamics. The MCWF method
identifies decay rates with jump probabilities and fails for non-Markovian
systems where the time-dependent rates become temporarily negative. Our
non-Markovian quantum jump (NMQJ) approach circumvents this problem and
provides an efficient unravelling of the ensemble dynamics.Comment: 4 pages, 2 figures.V2: rewritten abstract and introduction, title
modified. V3: published version, new example case with photonic band ga
Lindblad and non--Lindblad type dynamics of a quantum Brownian particle
The dynamics of a typical open quantum system, namely a quantum Brownian
particle in a harmonic potential, is studied focussing on its non-Markovian
regime. Both an analytic approach and a stochastic wave function approach are
used to describe the exact time evolution of the system. The border between two
very different dynamical regimes, the Lindblad and non-Lindblad regimes, is
identified and the relevant physical variables governing the passage from one
regime to the other are singled out. The non-Markovian short time dynamics is
studied in detail by looking at the mean energy, the squeezing, the Mandel
parameter and the Wigner function of the system.Comment: 13 pages, 4 figures, v2:added discussion on Wigner function,
squeezing, and Mandel paramete
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