453 research outputs found
The role of quasi-momentum in the resonant dynamics of the atom-optics kicked rotor
We examine the effect of the initial atomic momentum distribution on the
dynamics of the atom-optical realisation of the quantum kicked rotor. The atoms
are kicked by a pulsed optical lattice, the periodicity of which implies that
quasi-momentum is conserved in the transport problem. We study and compare
experimentally and theoretically two resonant limits of the kicked rotor: in
the vicinity of the quantum resonances and in the semiclassical limit of
vanishing kicking period. It is found that for the same experimental
distribution of quasi-momenta, significant deviations from the kicked rotor
model are induced close to quantum resonance, while close to the classical
resonance (i.e. for small kicking period) the effect of the quasi-momentum
vanishes.Comment: 10 pages, 4 figures, to be published in J. Phys. A, Special Issue on
'Trends in Quantum Chaotic Scattering
Dissipation induced coherence of a two-mode Bose-Einstein condensate
We discuss the dynamics of a Bose-Einstein condensate in a double-well trap
subject to phase noise and particle loss. The phase coherence of a
weakly-interacting condensate as well as the response to an external driving
show a pronounced stochastic resonance effect: Both quantities become maximal
for a finite value of the dissipation rate matching the intrinsic time scales
of the system. Even stronger effects are observed when dissipation acts in
concurrence with strong inter-particle interactions, restoring the purity of
the condensate almost completely and increasing the phase coherence
significantly.Comment: 10 pages, 5 figure
Dissipation induced macroscopic entanglement in an open optical lattice
We introduce a method for the dissipative preparation of strongly correlated
quantum states of ultracold atoms in an optical lattice via localized particle
loss. The interplay of dissipation and interactions enables different types of
dynamics. This ushers a new line of experimental methods to maintain the
coherence of a Bose-Einstein condensate or to deterministically generate
macroscopically entangled quantum states.Comment: 4 figure
Transient localization in the kicked Rydberg atom
We investigate the long-time limit of quantum localization of the kicked
Rydberg atom. The kicked Rydberg atom is shown to possess in addition to the
quantum localization time a second cross-over time where quantum
dynamics diverges from classical dynamics towards increased instability. The
quantum localization is shown to vanish as either the strength of the kicks at
fixed principal quantum number or the quantum number at fixed kick strength
increases. The survival probability as a function of frequency in the transient
localization regime is characterized by highly irregular,
fractal-like fluctuations
Quantum to Classical Walk Transitions Tuned by Spontaneous Emissions
We have recently realized a quantum walk in momentum space with a rubidium spinor BoseEinstein condensate by applying a periodic kicking potential as a walk operator and a resonant microwave pulse as a coin toss operator. The generated quantum walks appear to be stable for up to ten steps and then quickly transit to classical walks due to spontaneous emissions induced by laser beams of the walk operator. We investigate these quantum to classical walk transitions by introducing well-controlled spontaneous emissions with an external light source during quantum walks. Our findings demonstrate a scheme to control the robustness of the quantum walks and can also be applied to other cold atom experiments involving spontaneous emissions
Light shift induced behaviors observed in momentum-space quantum walks
Quantum walks (QWs) have seen many advances both experimentally and theoretically over the last decade with many proposed applications. Recently, a QW was experimentally realized utilizing a Bose-Einstein Condensate (BEC) in momentum space. This QW was observed to be stable up to fifteen steps and exhibited behavior that agreed generally well with theoretical predictions. However, the QW also showed interesting behavior within the momentum distribution that wasn’t adequately explained by the theory. We propose a new theoretical model to offer an explanation based upon the parameters within the conducted experiments. This model also predicts that the discrepancy is dependent upon the initial momentum states used in creating the QW
Many Body Quantum Chaos
This editorial remembers Shmuel Fishman, one of the founding fathers of the research field "quantum chaos", and puts into context his contributions to the scientific community with respect to the twelve papers that form the special issue
Engineering transport by concatenated maps
We present a generalized kick rotor model in which the phase of the kick can
vary from kick to kick. This additional freedom allows one to control the
transport in phase space. For a specific choice of kick-to-kick phases, we
predict novel forms of accelerator modes which are potentially of high
relevance for future experimental studies
Can quantum fractal fluctuations be observed in an atom-optics kicked rotor experiment?
We investigate the parametric fluctuations in the quantum survival
probability of an open version of the delta-kicked rotor model in the deep
quantum regime. Spectral arguments [Guarneri I and Terraneo M 2001 Phys. Rev. E
vol. 65 015203(R)] predict the existence of parametric fractal fluctuations
owing to the strong dynamical localisation of the eigenstates of the kicked
rotor. We discuss the possibility of observing such dynamically-induced
fractality in the quantum survival probability as a function of the kicking
period for the atom-optics realisation of the kicked rotor. The influence of
the atoms' initial momentum distribution is studied as well as the dependence
of the expected fractal dimension on finite-size effects of the experiment,
such as finite detection windows and short measurement times. Our results show
that clear signatures of fractality could be observed in experiments with cold
atoms subjected to periodically flashed optical lattices, which offer an
excellent control on interaction times and the initial atomic ensemble.Comment: 18 pp, 7 figs., 1 tabl
Non-hermitian approach to decaying ultracold bosonic systems
A paradigm model of modern atom optics is studied, strongly interacting
ultracold bosons in an optical lattice. This many-body system can be
artificially opened in a controlled manner by modern experimental techniques.
We present results based on a non-hermitian effective Hamiltonian whose quantum
spectrum is analyzed. The direct access to the spectrum of the metastable
many-body system allows us to easily identify relatively stable quantum states,
corresponding to previously predicted solitonic many-body structures
- …