30 research outputs found
Non-Markovian probes in ultracold gases
We present a detailed investigation of the dynamics of two physically
different qubit models, dephasing under the effect of an ultracold atomic gas
in a Bose-Einstein condensed (BEC) state. We study the robustness of each qubit
probe against environmental noise; even though the two models appear very
similar at a first glance, we demonstrate that they decohere in a strikingly
different way. This result holds significance for studies of reservoir
engineering as well as for using the qubits as quantum probes of the ultracold
gas. For each model we study whether and when, upon suitable manipulation of
the BEC, the dynamics of the qubit can be described by a (non-)Markovian
process and consider the the effect of thermal fluctuations on the qubit
dynamics. Finally, we provide an intuitive explanation for the phenomena we
observe in terms of the spectral density function of the environment.Comment: 6 pages, 4 figure
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
Single-atom interferometer based on two-dimensional spatial adiabatic passage
In this work we propose a novel single-atom interferometer based on a fully
two-dimensional spatial adiabatic passage process using a system of three
identical harmonic traps in a triangular geometry. While the transfer of a
single atom from the ground state of one trap to the ground state of the most
distant one can successfully be achieved in a robust way for a broad range of
parameter values, we point out the existence of a specific geometrical
configuration of the traps for which a crossing of two energy eigenvalues
occurs and the transfer of the atom fails. Instead the wavefunction is robustly
split into a coherent superposition between two of the traps. We show that this
process can be used to construct a single-atom interferometer and discuss its
performance in terms of the final population distribution among the asymptotic
eigenstates of the individual traps. This interferometric scheme could be used
to study space dependent fields from ultrashort to relatively large distances,
or the decay of the coherence of superposition states as a function of the
distance.Comment: 8 pages, 9 figure
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
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
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