21 research outputs found
Two atomic quantum dots interacting via coupling to BECs
We consider a system of three weakly coupled Bose-Einstein condensates and
two atomic quantum dots embedded in the barriers between the condensates. Each
dot is coupled to two neighboring condensates by optical transitions and can be
described as a two-state system, or a pseudospin 1/2. Although there is no
direct coupling between the dots, an effective interaction between the
pseudospins is induced due to their coupling to the condensate reservoirs. We
investigate this effective interaction, depending on the strengths of the
dot-condensate coupling T and the direct coupling J between the condensates. In
particular, we show that an initially ferromagnetic arrangement of the two
pseudospins stays intact even for large T/J. However, antiferromagnetically
aligned spins undergo peculiar "breathing" modes for weak coupling T/J<1, while
for strong coupling the behaviour of the spins becomes uncorrelated.Comment: 5 pages, 7 figure
A Quantum Top Inside a Bose Josephson Junction
We consider an atomic quantum dot confined between two weakly-coupled
Bose-Einstein condensates, where the dot serves as an additional tunneling
channel. It is shown that the thus-embedded atomic quantum dot is a pseudospin
subject to an external torque, and therefore equivalent to a quantum top. We
demonstrate by numerical analysis of the time-dependent coupled evolution
equations that this microscopic quantum top is very sensitive to any deviation
from linear oscillatory behavior of the condensates. For sufficiently strong
dot-condensate coupling, the atomic quantum dot can induce or modify the
tunneling between the macroscopic condensates in the two wells.Comment: 4 pages of RevTex4, 4 figures; rewritten discussion and displayed new
result
Entanglement generation in a system of two atomic quantum dots coupled to a pool of interacting bosons
We discuss entanglement generation in a closed system of one or two atomic
quantum dots (qubits) coupled via Raman transitions to a pool of cold
interacting bosons. The system exhibits rich entanglement dynamics, which we
analyze in detail in an exact quantum mechanical treatment of the problem. The
bipartite setup of only one atomic quantum dot coupled to a pool of bosons
turns out to be equivalent to two qubits which easily get entangled being
initially in a product state. We show that both the number of bosons in the
pool and the boson-boson interaction crucially affect the entanglement
characteristics of the system. The tripartite system of two atomic quantum dots
and a pool of bosons reduces to a qubit-qutrit-qubit realization. We consider
entanglement possibilities of the pure system as well as of reduced ones by
tracing out one of the constituents, and show how the entanglement can be
controlled by varying system parameters. We demonstrate that the qutrit, as
expected, plays a leading role in entangling of the two qubits and the maximum
entanglement depends in a nontrivial way on the pool characteristics.Comment: 16 pages, 6 figure
Coherent single atom shuttle between two Bose-Einstein condensates
We study an atomic quantum dot representing a single hyperfine "impurity"
atom which is coherently coupled to two well-separated Bose-Einstein
condensates, in the limit when the coupling between the dot and the condensates
dominates the inter-condensate tunneling coupling. It is demonstrated that the
quantum dot by itself can induce large-amplitude Josephson-like oscillations of
the particle imbalance between the condensates, which display a two-frequency
behavior. For noninteracting condensates, we provide an approximate solution to
the coupled nonlinear equations of motion which allows us to obtain these two
frequencies analytically.Comment: 4 pages of RevTex4, 4 figures; Rapid Communication in Physical Review
Chaos onset in large rings of Bose-Einstein condensates
We consider large rings of weakly-coupled Bose-Einstein condensates,
analyzing their transition to chaotic dynamics and loss of coherence.
Initially, a ring is considered to be in an eigenstate, i.e. in a commensurate
configuration with equal site fillings and equal phase differences between
neighboring sites. Such a ring should exhibit a circulating current whose value
will depend on the initial, non-zero phase difference. The appearance of such
currents is a signature of an established coherence along the ring. If phase
difference falls between and and interparticle interaction in
condensates exceeds a critical interaction value , the coherence is
supposed to be quickly destroyed because the system enters a chaotic regime due
to inherent instabilities. This is, however, only a part of the story. It turns
out that chaotic dynamics and resulting averaging of circular current to zero
is generally offset by a critical time-scale , which is almost two orders
of magnitude larger than the one expected from the linear stability analysis.
We study the critical time-scale in detail in a broad parameter range.Comment: 11 pages, 12 figure
Nonequilibrium Josephson oscillations in Bose-Einstein condensates without dissipation
We perform a detailed field theoretical study of nonequilibrium Josephson
oscillations between interacting Bose-Einstein condensates confined in a
finite-size double-well trap. We find that the Josephson junction can sustain
multiple undamped Josephson oscillations up to a characteristic time scale
without quasipartcles being excited in the system. This may explain
recent related experiments. At larger times the dynamics of the junction is
governed by fast Rabi oscillations between the descrete quasiparticle levels.
We predict that a selftrapped BEC state will be destroyed by these Rabi
oscillations.Comment: 4 pages, 4 figures, final versio
Interplay of Phonon and Exciton-Mediated Superconductivity in Hybrid Semiconductor-Superconductor Structures
We predict a strong enhancement of the critical temperature in a conventional
Bardeen-Cooper-Schrieffer (BCS) superconductor in the presence of a bosonic
condensate of exciton-polaritons. The effect depends strongly on the ratio of
the cutoff frequencies for phonon and exciton-polariton mediated BCS
superconductivity, respectively. We also discuss a possible design of hybrid
semiconductor-superconductor structures suitable for the experimental
observation of such an effect.Comment: 5 pages, 3 figures, accepted in Phys. Rev. Let