135 research outputs found
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
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
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
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
Kuramoto synchronization of quantum tunneling polarons for describing the structure in cuprate superconductors
A major open topic in cuprates is the interplay between the lattice and electronic dynamics and the importance of their coupling to the mechanism of high-temperature superconductivity (HTSC). As evidenced by extended xray absorption fine structure (EXAFS) experiments, anharmonic structural effects are correlated with the charge dynamics and the transition to a superconducting phase in different HTSC compounds. Here we describe how structural anharmonic effects can be coupled to electronic and lattice dynamics in cuprate systems by performing the exact diagonalization of a prototype anharmonic many-body Hamiltonian on a relevant 6-atom cluster and show that the EXAFS results can be understood as a Kuramoto synchronization transition between coupled internal quantum tunneling of polarons associated with the two-site distribution of the copper-apical oxygen (Cu-Oap) pair in the dynamic structure. The transition is driven by the anharmonicity of the lattice vibrations and promotes the pumping of charge, initially stored at the apical oxygen reservoirs, into the copper-oxide plane. Simultaneously, a finite projection of the internal quantum tunneling polaron extends to the copper-planar oxygen (Cu-Opl) pair. All these findings allow an interpretation based on an effective quantum-mechanical triple well potential associated with the oxygen sites of the 6-atom cluster, which accurately represents the phase synchronization of apical oxygens and lattice-assisted charge transfer to the CuO2 plane
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
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
- …