20 research outputs found
A quantum motor: directed wavepacket motion in an optical lattice
We propose a method for arbitrary manipulations of a quantum wavepacket in an
optical lattice by a suitable modulation of the lattice amplitude. A
theoretical model allows to determine the modulation corresponding to a given
wavepacket motion, so that arbitrary atomic trajectories can be generated. The
method is immediately usable in state of the art experiments
Tracking quasi-classical chaos in ultracold boson gases
We study the dynamics of a ultra-cold boson gas in a lattice submitted to a
constant force. We track the route of the system towards chaos created by the
many-body-induced nonlinearity and show that relevant information can be
extracted from an experimentally accessible quantity, the gas mean position.
The threshold nonlinearity for the appearance of chaotic behavior is deduced
from KAM arguments and agrees with the value obtained by calculating the
associated Lyapunov exponent.Comment: 4 pages, revtex4, submitted to PR
Doppler cooling to the recoil limit using sharp atomic transitions
In this paper, we develop an analytical approach to Doppler cooling of atoms
by one- or two-photon transitions when the natural width of the excited level
is so small that the process leads to a Doppler temperature comparable to the
recoil temperature. A ``quenching'' of the sharp line is introduced in order to
allow control of the time scale of the problem. In such limit, the usual
Fokker-Planck equation does not correctly describe the cooling process. We
propose a generalization of the Fokker-Planck equation and derive a new model
which is able to reproduce correctly the numerical results, up to the recoil
limit. Two cases of practical interest, one-photon Doppler cooling of strontium
and two-photon Doppler cooling of hydrogen are considered.Comment: 5 pages, RevTex 4, submitted to JOSA B (special issue "laser cooling
of atoms"
Classical chaos with Bose-Einstein condensates in tilted optical lattices
A widely accepted definition of ``quantum chaos'' is ``the behavior of a
quantum system whose \emph{classical} \emph{limit is chaotic}''. The dynamics
of quantum-chaotic systems is nevertheless very different from that of their
classical counterparts. A fundamental reason for that is the linearity of
Schr{\"o}dinger equation. In this paper, we study the quantum dynamics of an
ultra-cold quantum degenerate gas in a tilted optical lattice and show that it
displays features very close to \emph{classical} chaos. We show that its phase
space is organized according to the Kolmogorov-Arnold-Moser theorem.Comment: 4 pages, 3 figure
Continuous-wave Doppler-cooling of hydrogen atoms with two-photon transitions
We propose and analyze the possibility of performing two-photon
continuous-wave Doppler-cooling of hydrogen atoms using the 1S-2S transition.
"Quenching" of the 2S level (by coupling with the 2P state) is used to increase
the cycling frequency, and to control the equilibrium temperature. Theoretical
and numerical studies of the heating effect due to Doppler-free two-photon
transitions evidence an increase of the temperature by a factor of two. The
equilibrium temperature decreases with the effective (quenching dependent)
width of the excited state and can thus be adjusted up to values close to the
recoil temperature.Comment: 11 pages, 4 figures in eps forma
Atomic Dipole Traps with Amplified Spontaneous Emission: A Proposal
We propose what we believe to be a novel type of optical source for
ultra-cold atomic Far Off-Resonance optical-dipole Traps (FORTs). The source is
based on an Erbium Amplified Spontaneous Emission (ASE) source that seeds a
high power Erbium Doped Fiber Amplifier (EDFA). The main interest of this
source is its very low coherence length, thus allowing an incoherent
superposition of several trapping beams without any optical interference. The
behavior of the superimposed beams is then a scalar sum greatly simplifying
complex configurations. As an illustration, we report an estimation of the
intensity noise of this source and an estimation of the atomic excess heating
rate for an evaporative cooling experiment application. They are both found to
be suitable for cold atoms experiments
Theoretical analysis of quantum dynamics in 1D lattices: Wannier-Stark description
This papers presents a formalism describing the dynamics of a quantum
particle in a one-dimensional tilted time-dependent lattice. The description
uses the Wannier-Stark states, which are localized in each site of the lattice
and provides a simple framework leading to fully-analytical developments.
Particular attention is devoted to the case of a time-dependent potential,
which results in a rich variety of quantum coherent dynamics is found.Comment: 8 pages, 6 figures, submitted to PR