26 research outputs found
Vortex entanglement in Bose-Einstein condensates coupled to Laguerre-Gauss beams
We study the establishment of vortex entanglement in remote and weakly
interacting Bose Einstein condensates. We consider a two-mode photonic resource
entangled in its orbital angular momentum (OAM) degree of freedom and, by
exploiting the process of light-to-BEC OAM transfer, demonstrate that such
entanglement can be efficiently passed to the matter-like systems. Our proposal
thus represents a building block for novel low-dissipation and long-memory
communication channels based on OAM. We discuss issues of practical
realizability, stressing the feasibility of our scheme and present an operative
technique for the indirect inference of the set vortex entanglement.Comment: 10 pages, 7 figures, RevTex
Two-qubit non-Markovianity induced by a common environment
We study non-Markovianity as backflow of information in two-qubit systems. We
consider a setting where, by changing the distance between the qubits, one can
interpolate between independent reservoir and common reservoir scenarios. We
demonstrate that non-Markovianity can be induced by the common reservoir and
single out the physical origin of this phenomenon. We show that two-qubit
non-Markovianity coincides with instances of non-divisibility of the
corresponding dynamical map, and we discuss the pair of states maximizing
information flowback. We also discuss the issue of additivity for the measure
we use and in doing so, give an indication of its usefulness as a resource for
multipartite quantum systems.Comment: 9 pages, 5 figures, Published version with minor modification
Vortex Dynamics in Anisotropic Traps
We investigate the dynamics of linear vortex lattices in anisotropic traps in
two-dimensions and show that the interplay between the rotation and the
anisotropy leads to a rich but highly regular dynamics.Comment: 6 pages, 6 figure
Non-Markovianity, Loschmidt echo and criticality: a unified picture
A simple relationship between recently proposed measures of non-Markovianity
and the Loschmidt echo is established, holding for a two-level system (qubit)
undergoing pure dephasing due to a coupling with a many-body environment. We
show that the Loschmidt echo is intimately related to the information flowing
out from and occasionally back into the system. This, in turn, determines the
non-Markovianity of the reduced dynamics. In particular, we consider a central
qubit coupled to a quantum Ising ring in the transverse field. In this context,
the information flux between system and environment is strongly affected by the
environmental criticality; the qubit dynamics is shown to be Markovian exactly
and only at the critical point. Therefore non-Markovianity is an indicator of
criticality in the model considered here
Small Numbers of Vortices in Anisotropic Traps
We investigate the appearance of vortices and vortex lattices in
two-dimensional, anisotropic and rotating Bose-Einstein condensates. Once the
anisotropy reaches a critical value, the positions of the vortex cores in the
ground state are no longer given by an Abrikosov lattice geometry, but by a
linear arrangement. Using a variational approach, we determine the critical
stirring frequency for a single vortex as well as the equilibrium positions of
a small number of vortices.Comment: 7 pages, 7 figure
Interspecies entanglement with impurity atoms in a lattice gas
The dynamics of impurity atoms introduced into bosonic gases in an optical lattice have generated a lot of recent interest, both in theory and experiment. We investigate to what extent measurements on either the impurity species or the majority species in these systems are affected by their interspecies entanglement. This arises naturally in the dynamics and plays an important role when we measure only one species. We explore the corresponding effects in strongly interacting regimes, using a combination of few-particle analytical calculations and density matrix renormalisation group methods in one dimension. We identify how the resulting effects on impurities can be used to probe the many-body states of the majority species, and separately ask how to enter regimes where this entanglement is small, so that the impurities can be used as probes that do not significantly affect the majority species. The results are accessible in current experiments, and provide important considerations for the measurement of complex systems with using few probe atoms
Tunneling-induced angular momentum for single cold atoms
We study the generation of angular momentum carrying states for a single cold
particle by breaking the symmetry of a spatial adiabatic passage process in a
two-dimensional system consisting of three harmonic potential wells. By
following a superposition of two eigenstates of the system, a single cold
particle is completely transferred to the degenerate first excited states of
the final trap, which are resonantly coupled via tunneling to the ground states
of the initial and middle traps. Depending on the total time of the process,
angular momentum is generated in the final trap, with values that oscillate
between . This process is discussed in terms of the asymptotic
eigenstates of the individual wells and the results have been checked by
simulations of the full two-dimensional Schr\"odinger equation.Comment: 6 pages, 5 figure
Impact of anisotropy on vortex clusters and their dynamics
We investigate the effects of anisotropy on the stability and dynamics of
vortex cluster states which arise in Bose-Einstein condensates. Sufficiently
strong anisotropies are shown to stabilize states with arbitrary numbers of
vortices that are highly unstable in the isotropic limit. Conversely,
anisotropy can be used to destabilize states which are stable in the isotropic
limit. Near the linear limit, we identify the bifurcations of vortex states
including their emergence from linear eigenstates, while in the strongly
nonlinear limit, a particle-like description of the dynamics of the vortices in
the anisotropic trap is developed. Both are in very good agreement with
numerical results. Collective modes of stabilized many vortex cluster states
are demonstrated.Comment: 6 pages, 6 figure
Robust non-Markovianity in ultracold gases
We study the effect of thermal fluctuations on a probe qubit interacting with
a Bose-Einstein condensed (BEC) reservoir. The zero-temperature case was
studied in [Haikka P et al 2011 Phys. Rev. A 84 031602], where we proposed a
method to probe the effects of dimensionality and scattering length of a BEC
based on its behavior as an environment. Here we show that the sensitivity of
the probe qubit is remarkably robust against thermal noise. We give an
intuitive explanation for the thermal resilience, showing that it is due to the
unique choice of the probe qubit architecture of our model.Comment: Submitted to FQMT11 topical issue of the Physica Script