8,147 research outputs found
Interaction of bimodal fields with few-level atoms in cavities and traps
The spectacular experimental results of the last few years in cavity quantum
electrodynamics and trapped ions research has led to very high level laboratory
performances. Such a stimulating situation essentially stems from two decisive
advancements. The first is the invention of reliable protocols for the
manipulation of single atoms. The second is the ability to produce desired
bosonic environments on demand. These progresses have led to the possibility of
controlling the form of the coupling between individual atoms and an arbitrary
number of bosonic modes. As a consequence, fundamental matter-radiation
interaction models like, for instance, the JC model and most of its numerous
nonlinear multiphoton generalizations, have been realized or simulated in
laboratory and their dynamical features have been tested more or less in
detail. This topical paper reviews the state of the art of the theoretical
investigations and of the experimental observations concerning the dynamical
features of the coupling between single few-level atoms and two bosonic modes.
In the course of the paper we show that such a configuration provides an
excellent platform for investigating various quantum intermode correlation
effects tested or testable in the cavity quantum electrodynamics and trapped
ion experimental realms. In particular we discuss a mode-mode correlation
effect appearing in the dynamics of a two-level atom quadratically coupled to
two bosonic modes. This effect, named parity effect, consists in a high
sensitivity to the evenness or oddness of the total number of bosonic
excitations.Comment: Topical Review. To appear on J. Mod. Op
The rotating wave system-reservoir coupling: limitations and meaning in the non-Markovian regime
This paper deals with the dissipative dynamics of a quantum harmonic
oscillator interacting with a bosonic reservoir. The Master Equations based on
the Rotating Wave and on the Feynman-Vernon system--reservoir couplings are
compared highlighting differences and analogies. We discuss quantitatively and
qualitatively the conditions under which the counter rotating terms can be
neglected. By comparing the analytic solution of the heating function relative
to the two different coupling models we conclude that, even in the weak
coupling limit, the counter rotating terms give rise to a significant
contribution in the non--Markovian short time regime. The main result of this
paper is that such a contribution is actually experimentally measurable and
thus relevant for a correct description of the system dynamics.Comment: 14 pages, 3 figure
Loss induced collective subradiant Dicke behaviour in a multiatom sample
The exact dynamics of two-level atoms coupled to a common electromagnetic
bath and closely located inside a lossy cavity is reported. Stationary
radiation trapping effects are found and very transparently interpreted in the
context of our approach. We prove that initially injecting one excitation only
in the atoms-cavity system, loss mechanisms asymptotically drive the matter
sample toward a long-lived collective subradiant Dicke state. The role played
by the closeness of the atoms with respect to such a cooperative behavior
is brought to light and carefully discussed.Comment: 14 pages, 6 figures, submitted to EPJ
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
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
Stationary entanglement induced by dissipation
The dynamics of two two-level dipole-dipole interacting atoms coupled to a
common electromagnetic bath and closely located inside a lossy cavity, is
reported. Initially injecting only one excitation in the two atoms-cavity
system, loss mechanisms asymptotically drive the matter sample toward a
stationary maximally entangled state. The role played by the closeness of the
two atoms with respect to such a cooperative behaviour is carefully discussed.
Stationary radiation trapping effects are found and transparently interpreted.Comment: 1 figure, submitted to Phys. Rev. Let
Dynamics of a particle confined in a two-dimensional dilating and deforming domain
Some recent results concerning a particle confined in a one-dimensional box
with moving walls are briefly reviewed. By exploiting the same techniques used
for the 1D problem, we investigate the behavior of a quantum particle confined
in a two-dimensional box (a 2D billiard) whose walls are moving, by recasting
the relevant mathematical problem with moving boundaries in the form of a
problem with fixed boundaries and time-dependent Hamiltonian. Changes of the
shape of the box are shown to be important, as it clearly emerges from the
comparison between the "pantographic", case (same shape of the box through all
the process) and the case with deformation.Comment: 13 pages, 2 figure
RACE-OC Project: Rotation and variability in the open cluster M11 (NGC6705)
Rotation and magnetic activity are intimately linked in main-sequence stars
of G or later spectral types. The presence and level of magnetic activity
depend on stellar rotation, and rotation itself is strongly influenced by
strength and topology of the magnetic fields. Open clusters represent
especially useful targets to investigate the rotation/activity/age connection.
The open cluster M11 has been studied as a part of the RACE-OC project
(Rotation and ACtivity Evolution in Open Clusters), which is aimed at exploring
the evolution of rotation and magnetic activity in the late-type members of
open clusters with different ages. Photometric observations of the open cluster
M11 were carried out in June 2004 using LOAO 1m telescope. The rotation periods
of the cluster members are determined by Fourier analysis of photometric data
time series. We further investigated the relations between the surface
activity, characterized by the light curve amplitude, and rotation. We have
discovered a total of 75 periodic variables in the M11 FoV, of which 38 are
candidate cluster members. Specifically, among cluster members we discovered 6
early-type, 2 eclipsing binaries and 30 bona-fide single periodic late-type
variables. Considering the rotation periods of 16 G-type members of the almost
coeval 200-Myr M34 cluster, we could determine the rotation period distribution
from a more numerous sample of 46 single G stars at an age of about 200-230 Myr
and determine a median rotation period P=4.8d. A comparison with the younger
M35 cluster (~150 Myr) and with the older M37 cluster (~550 Myr) shows that G
stars rotate slower than younger M35 stars and faster than older M37 stars. The
measured variation of the median rotation period is consistent with the
scenario of rotational braking of main-sequence spotted stars as they age.Comment: Accepted by Astronomy and Astrophysics on Dec 15, 200
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