Spontaneous Emission in Quantum Walks of a Kicked Bose-Einstein Condensate

We analytically investigate the recently proposed and implemented discrete-time quantum walk based on a kicked Bose-Einstein condensate. We extend previous work on the effective dynamics by taking into account spontaneous emission due to the kicking light. Spontaneous emission affects both the internal and external degrees of freedom, arising from the entanglement between them during the walk dynamics. The result is a measurable degrading of the experimental walk signal that we characterise.Comment: comments and suggestions welcom

Induced Delocalization by Correlation and Interaction in the one-dimensional Anderson Model

We consider long-range correlated disorder and mutual interacting particles according to a dipole-dipole coupling as modifications to the one-dimensional Anderson model. Technically we rely on the (numerical) exact diagonalization of the system's Hamilitonian. From the perspective of different localization measures we confirm and extend the picture of the emergence of delocalized states with increasing correlations. Beside these studies a definition for multi-particle localization is proposed. In the case of two interacting bosons we observe a sensitivity of localization with respect to the range of the particle-particle interaction and insensitivity to the coupling's sign, which should stimulate new theoretical approaches and experimental investigations with e.g. dipolar cold quantum gases. This revised manuscript is much more explicit compared to the initial version of the paper. Major extensions have been applied to Sects. II and III where we updated and added figures and we more extensively compared our results to the literature. Furthermore, Sect. III additionally contains a phenomenological line of reasoning that bridges from delocalization by correlation to delocalization by interaction on the basis of the multi-particle Hamilton matrix

Quantum walk of a Bose-Einstein condensate in the Brillouin zone

We propose a realistic scheme to implement discrete-time quantum walks in the Brillouin zone (i.e., in quasimomentum space) with a spinor Bose-Einstein condensate. Relying on a static optical lattice to suppress tunneling in real space, the condensate is displaced in quasimomentum space in discrete steps conditioned upon the internal state of the atoms, while short pulses periodically couple the internal states. We show that tunable twisted boundary conditions can be implemented in a fully natural way by exploiting the periodicity of the Brillouin zone. The proposed setup does not suffer from off-resonant scattering of photons and could allow a robust implementation of quantum walks with several tens of steps at least. In addition, onsite atom-atom interactions can be used to simulate interactions with infinitely long range in the Brillouin zone.Comment: 9 pages, 4 figures; in the new version, added a discussion about decoherence in the appendi

Signatures of Anderson localization in the ionization rates of periodically driven Rydberg states

We provide a statistical characterization of the ionization yield of one-dimensional, periodically driven Rydberg states of atomic hydrogen, in the spirit of Anderson localization theory. We find excellent agreement with predictions for the conductance across an Anderson localized, quasi one-dimensional, disordered wire, in the semiclassical limit of highly excited atomic initial states. For the moderate atomic excitations typically encountered in state of the art laboratory experiments, finite-size effects induce significant deviations from the solid-state picture. However, large scale fluctuations of the atomic conductance prevail and are robust when averaged over a finite interval of driving field amplitudes, as inevitably done in the experiment.Comment: 13 pages, 9 figure

Tunneling of ultracold atoms in time-independent potentials

We present theoretical as well as experimental results on resonantly enhanced quantum tunneling of Bose-Einstein condensates in optical lattices both in the linear case of single particle dynamics and in the presence of atom-atom interactions. Our results demonstrate the usefulness of condensates in optical lattices for the dynamical control of tunneling and for simulating Hamiltonians originally used for describing solid state phenomena.Comment: slightly amended version published as ch. 11 of a book edited by S. Keshavamurthy and P. Schlagheck with the title "Dynamical Tunneling: Theory and Experiment

Mean-field transport of a Bose-Einstein condensate

The expansion of an initially confined Bose-Einstein condensate into either free space or a tilted optical lattice is investigated in a mean-field approach. The effect of the interactions is to enhance or suppress the transport depending on the sign and strength of the interactions. These effects are discusses in detail in view of recent experiments probing non-equilibrium transport of ultracold quantum gases

Dynamical enhancement of spatial entanglement in massive particles

We discuss dynamical enhancement of entanglement in a driven Bose-Hubbard model and find an enhancement of two orders of magnitude which is robust against fluctuations in experimental parameters.Comment: 4 pages, 4 figure

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

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