161 research outputs found
Spin-orbit coupled Bose-Einstein condensates in a double well
We study the quantum dynamics of a spin-orbit (SO) coupled Bose-Einstein
condensate (BEC) in a double-well potential inspired by the experimental
protocol recently developed by NIST group. We focus on the regime where the
number of atoms is very large and perform a two-mode approximation. An
analytical solution of the two-site Bose-Hubbard-like Hamiltonian is found for
several limiting cases, which range from a strong Raman coupling to a strong
Josephson coupling, ending with the complete model in the presence of weak
nonlinear interactions. Depending on the particular limit, different approaches
are chosen: a mapping onto an SU(2) spin problem together with a
Holstein-Primakoff transformation in the first two cases and a rotating wave
approximation (RWA) when dealing with the complete model. The quantum evolution
of the number difference of bosons with equal or different spin between the two
wells is investigated in a wide range of parameters; finally the corresponding
total atomic current and the spin current are computed. We show a spin
Josephson effect which could be detected in experiments and employed to build
up realistic devices.Comment: 18 page
Incompressible states of a two-component Fermi gas in a double-well optical lattice
We propose a scheme to investigate the effect of frustration on the magnetic
phase transitions of cold atoms confined in an optical lattice. We also
demonstrate how to get two-leg spin ladders with frustrated spin-exchange
coupling which display a phase transition from a spin liquid to a fully
incompressible state. Various experimental quantities are further analyzed for
describing this phase.Comment: 10 pages, 7 figures. Published in Phys. Rev.
Fractional quantization of the topological charge pumping in a one-dimensional superlattice
A one-dimensional quantum charge pump transfers a quantized charge in each
pumping cycle. This quantization is topologically robust being analogous to the
quantum Hall effect. The charge transferred in a fraction of the pumping period
is instead generally unquantized. We show, however, that with specific
symmetries in parameter space the charge transferred at well-defined fractions
of the pumping period is quantized as integer fractions of the Chern number. We
illustrate this in a one-dimensional Harper-Hofstadter model and show that the
fractional quantization of the topological charge pumping is independent of the
specific boundary conditions taken into account. We further discuss the
relevance of this phenomenon for cold atomic gases in optical superlattices.Comment: 8 pages, 7 figures, new material adde
Nonequilibrium properties of an atomic quantum dot coupled to a Bose-Einstein condensate
We study nonequilibrium properties of an atomic quantum dot (AQD) coupled to
a Bose-Einstein condensate (BEC) within Keldysh-Green's function formalism when
the AQD level is varied harmonically in time. Nonequilibrium features in the
AQD energy absorption spectrum are the side peaks that develop as an effect of
photon absorption and emission. We show that atoms can be efficiently
transferred from the BEC into the AQD for the parameter regime of current
experiments with cold atoms.Comment: 8 pages, 2 figures, to appear in the special issue "Novel Quantum
Phases and Mesoscopic Physics in Quantum Gases" of The European Physical
Journal - Special Topic
Superfluidity and Anderson localisation for a weakly interacting Bose gas in a quasiperiodic potential
Using exact diagonalisation and Density Matrix Renormalisation group (DMRG)
approach, we analyse the transition to a localised state of a weakly
interacting quasi-1D Bose gas subjected to a quasiperiodic potential. The
analysis is performed by calculating the superfluid fraction, density profile,
momentum distribution and visibility for different periodicities of the second
lattice and in the presence (or not) of a weak repulsive interaction. It is
shown that the transition is sharper towards the maximally incommensurate ratio
between the two lattice periodicities, and shifted to higher values of the
second lattice strength by weak repulsive interactions. We also relate our
results to recent experiments.Comment: 12 pages, 9 figures, RevTeX
Polar bosons in one-dimensional disordered optical lattices
We analyze the effects of disorder and quasi-disorder on the ground-state
properties of ultra-cold polar bosons in optical lattices. We show that the
interplay between disorder and inter-site interactions leads to rich phase
diagrams. A uniform disorder leads to a Haldane-insulator phase with finite
parity order, whereas the density-wave phase becomes a Bose-glass at very weak
disorder. For quasi-disorder, the Haldane insulator connects with a gapped
generalized incommesurate density wave without an intermediate critical region.Comment: 5 pages + 2 pages, 8 figure
Quantum Bose Josephson Junction with binary mixtures of BECs
We study the quantum behaviour of a binary mixture of Bose-Einstein
condensates (BEC) in a double-well potential starting from a two-mode
Bose-Hubbard Hamiltonian. We focus on the small tunneling amplitude regime and
apply perturbation theory up to second order. Analytical expressions for the
energy eigenvalues and eigenstates are obtained. Then the quantum evolution of
the number difference of bosons between the two potential wells is fully
investigated for two different initial conditions: completely localized states
and coherent spin states. In the first case both the short and the long time
dynamics is studied and a rich behaviour is found, ranging from small amplitude
oscillations and collapses and revivals to coherent tunneling. In the second
case the short-time scale evolution of number difference is determined and a
more irregular dynamics is evidenced. Finally, the formation of Schroedinger
cat states is considered and shown to affect the momentum distribution.Comment: 14 pages, 4 figure
Persisting Meissner state and incommensurate phases of hard-core boson ladders in a flux
The phase diagram of a half-filled hard core boson two-leg ladder in a flux
is investigated by means of numerical simulations based on the Density Matrix
Renormalization Group (DMRG) algorithm and bosonization. We calculate
experimentally accessible observables such as the momentum distribution, as
well as rung current, density wave and bond-order wave correlation functions,
allowing us to identify the Mott Meissner and Mott Vortex states. We follow the
transition from commensurate Meissner to incommensurate Vortex state at
increasing interchain hopping till the critical value [Piraud et al. Phys. Rev.
B v. 91, p. 140406 (2015)] above which the Meissner state is stable at any
flux. For flux close to , and below the critical hopping, we observe the
formation of a second incommensuration in the Mott Vortex state that could be
detectable in current experiments.Comment: RevTeX 4, 5 pages + 8 pages supplemental, 6 EPS figures; (v2)
references added, corrected the discussion of the Meissner state at high
interchain hoppin
- …