890 research outputs found
Dynamical generation of dark solitons in spin-orbit-coupled Bose-Einstein condensates
We numerically investigate the ground state, the Raman-driving dynamics and
the nonlinear excitations of a realized spin-orbit-coupled Bose-Einstein
condensate in a one-dimensional harmonic trap. Depending on the Raman coupling
and the interatomic interactions, three ground-state phases are identified:
stripe, plane wave and zero-momentum phases. A narrow parameter regime with
coexistence of stripe and zero-momentum or plane wave phases in real space is
found. Several sweep progresses across different phases by driving the Raman
coupling linearly in time is simulated and the non-equilibrium dynamics of the
system in these sweeps are studied. We find kinds of nonlinear excitations,
with the particular dark solitons excited in the sweep from the stripe phase to
the plane wave or zero-momentum phase within the trap. Moreover, the number and
the stability of the dark solitons can be controlled in the driving, which
provide a direct and easy way to generate dark solitons and study their
dynamics and interaction properties.Comment: 10 pages, 9 figur
Superfluid and magnetic states of an ultracold Bose gas with synthetic three-dimensional spin-orbit coupling in an optical lattice
We study ultracold bosonic atoms with the synthetic three-dimensional
spin-orbit (SO) coupling in a cubic optical lattice. In the superfluidity
phase, the lowest energy band exhibits one, two or four pairs of degenerate
single-particle ground states depending on the SO-coupling strengths, which can
give rise to the condensate states with spin-stripes for the weak atomic
interactions. In the deep Mott-insulator regime, the effective spin Hamiltonian
of the system combines three-dimensional Heisenberg exchange interactions,
anisotropy interactions and Dzyaloshinskii-Moriya interactions. Based on Monte
Carlo simulations, we numerically demonstrate that the resulting Hamiltonian
with an additional Zeeman field has a rich phase diagram with spiral, stripe,
vortex crystal, and especially Skyrmion crystal spin-textures in each xy-plane
layer. The obtained Skyrmion crystals can be tunable with square and hexagonal
symmetries in a columnar manner along the z axis, and moreover are stable
against the inter-layer spin-spin interactions in a large parameter region.Comment: 9 pages, 4 figures; title modified, references and discussions added;
accepted by PR
Valley-dependent gauge fields for ultracold atoms in square optical superlattices
We propose an experimental scheme to realize the valley-dependent gauge
fields for ultracold fermionic atoms trapped in a state-dependent square
optical lattice. Our scheme relies on two sets of Raman laser beams to engineer
the hopping between adjacent sites populated by two-component fermionic atoms.
One set of Raman beams are used to realize a staggered \pi-flux lattice, where
low energy atoms near two inequivalent Dirac points should be described by the
Dirac equation for spin-1/2 particles. Another set of laser beams with proper
Rabi frequencies are added to further modulate the atomic hopping parameters.
The hopping modulation will give rise to effective gauge potentials with
opposite signs near the two valleys, mimicking the interesting strain-induced
pseudo-gauge fields in graphene. The proposed valley-dependent gauge fields are
tunable and provide a new route to realize quantum valley Hall effects and
atomic valleytronics.Comment: 5+ pages, 2 figures; language polished, references and discussions
added; accepted by PR
Entanglement dynamics of two-qubit system in different types of noisy channels
In this paper, we study entanglement dynamics of a two-qubit extended
Werner-like state locally interacting with independent noisy channels, i.e.,
amplitude damping, phase damping and depolarizing channels. We show that the
purity of initial entangled state has direct impacts on the entanglement
robustness in each noisy channel. That is, if the initial entangled state is
prepared in mixed instead of pure form, the state may exhibit entanglement
sudden death (ESD) and/or be decreased for the critical probability at which
the entanglement disappear.Comment: 11 pages, 6 figure
Entanglement and quantum phase transition in alternating XY spin chain with next-nearest neighbour interactions
By using the method of density-matrix renormalization-group to solve the
different spin-spin correlation functions, the nearest-neighbouring
entanglement(NNE) and next-nearest-neighbouring entanglement(NNNE) of
one-dimensional alternating Heisenberg XY spin chain is investigated in the
presence of alternating nearest neighbour interactions of exchange couplings,
external magnetic fields and next-nearest neighbouring interactions. For
dimerized ferromagnetic spin chain, NNNE appears only above the critical
dimerized interaction, meanwhile, the dimerized interaction effects quantum
phase transition point and improves NNNE to a large value. We also study the
effect of ferromagnetic or antiferromagnetic next-nearest neighboring (NNN)
interactions on the dynamics of NNE and NNNE. The ferromagnetic NNN interaction
increases and shrinks NNE below and above critical frustrated interaction
respectively, while the antiferromagnetic NNN interaction always decreases NNE.
The antiferromagnetic NNN interaction results to a larger value of NNNE in
comparison to the case when the NNN interaction is ferromagnetic.Comment: 13 pages, 4 figures,. accepted by Chinese Physics B 2008 11 (in
press
Entanglement control in one-dimensional random XY spin chain
The entanglement in one-dimensional random XY spin systems where the
impurities of exchange couplings and the external magnetic fields are
considered as random variables is investigated by solving the different
spin-spin correlation functions and the average magnetization per spin. The
entanglement dynamics near particular locations of the system is also studied
when the exchange couplings (or the external magnetic fields) satisfy three
different distributions(the Gaussian distribution, double-Gaussian
distribution, and bimodal distribution). We find that the entanglement can be
controlled by varying the strength of external magnetic field and the different
distributions of impurities. Moreover, the entanglement of some
nearest-neighboring qubits can be increased for certain parameter values of the
three different distributions.Comment: 13 pages, 4 figure
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