9 research outputs found
Topological Phase Separation In Trapped Ultracold Fermionic Gases
We investigate the harmonically trapped 2D fermionic systems with a effective
spin-orbit coupling and intrinsic s-wave superfluidity under the local density
approximation, and find that there is a critical value for Zeeman field. When
the Zeeman field larger than the critical value, the topological superfluid
phases emerge and coexist with the normal superfluid phase, topological phase
separation, in the trapped region. Otherwise, the superfluid phase is
topologically trivial.Comment: 6 pages, 3 figure
Engineering entanglement for metrology with rotating matter waves
Entangled states of rotating, trapped ultracold bosons form a very promising scenario for quantum metrology. In order to employ such states for metrology, it is vital to understand their detailed form and the enhanced accuracy with which they could measure phase, in this case generated through rotation. In this work, we study the rotation of ultracold bosons in an asymmetric trapping potential beyond the lowest Landau level (LLL) approximation. We demonstrate that while the LLL can identify reasonably the critical frequency for a quantum phase transition and entangled state generation, it is vital to go beyond the LLL to identify the details of the state and quantify the quantum Fisher information (which bounds the accuracy of the phase measurement). We thus identify a new parameter regime for useful entangled state generation, amenable to experimental investigation
Topological superfluids on a lattice with non-Abelian gauge fields
Two-component fermionic superfluids on a lattice with an external non-Abelian
gauge field give access to a variety of topological phases in presence of a
sufficiently large spin imbalance. We address here the important issue of
superfluidity breakdown induced by spin imbalance by a self-consistent
calculation of the pairing gap, showing which of the predicted phases will be
experimentally accessible. We present the full topological phase diagram, and
we analyze the connection between Chern numbers and the existence of
topologically protected and non-protected edge modes. The Chern numbers are
calculated via a very efficient and simple method.Comment: 6 pages, 5 figures to be published in Europhysics Letter
Particles in non-Abelian gauge potentials - Landau problem and insertion of non-Abelian flux
We study charged spin-1/2 particles in two dimensions, subject to a
perpendicular non-Abelian magnetic field. Specializing to a choice of vector
potential that is spatially constant but non-Abelian, we investigate the Landau
level spectrum in planar and spherical geometry, paying particular attention to
the role of the total angular momentum J = L +S. After this we show that the
adiabatic insertion of non-Abelian flux in a spin-polarized quantum Hall state
leads to the formation of charged spin-textures, which in the simplest cases
can be identified with quantum Hall Skyrmions.Comment: 24 pages, 10 figures (with corrected legends
Fractional quantum Hall effect in a U(1)xSU(2) gauge field
We consider the bosonic fractional quantum Hall effect in the presence of a
non-Abelian gauge field in addition to the usual Abelian magnetic field. The
non-Abelian field breaks the twofold internal state degeneracy, but preserves
the Landau level degeneracy. Using exact diagonalization, we find that for
moderate non-Abelian field strengths the system's behaviour resembles a single
internal state quantum Hall system, while for stronger fields there is a phase
transition to either two internal state behaviour or the complete absence of
fractional quantum Hall plateaus. Usually the energy gap is reduced by the
presence of a non-Abelian field, but some non-Abelian fields appear to slightly
increase the gap of the and Read-Rezayi states.Comment: 15 pages, 8 figures, submitted to New J. Phy
Topological superfluid of spinless Fermi gases in p-band honeycomb optical lattices with on-site rotation
In this paper, we put forward to another route realizing topological
superfluid (TS). In contrast to conventional method, spin-orbit coupling and
external magnetic field are not requisite. Introducing an experimentally
feasible technique called on-site rotation (OSR) into p-band honeycomb optical
lattices for spinless Fermi gases and considering CDW and pairing on the same
footing, we investigate the effects of OSR on superfluidity. The results
suggest that when OSR is beyond a critical value, where CDW vanishes, the
system transits from a normal superfluid (NS) with zero TKNN number to TS
labeled by a non-zero TKNN number. In addition, phase transitions between
different TS are also possible
Fractional quantum Hall states of few bosonic atoms in geometric gauge fields
We employ the exact diagonalization method to analyze the possibility of
generating strongly correlated states in two-dimensional clouds of ultracold
bosonic atoms which are subjected to a geometric gauge field created by
coupling two internal atomic states to a laser beam. Tuning the gauge field
strength, the system undergoes stepwise transitions between different ground
states, which we describe by analytical trial wave functions, amongst them the
Pfaffian, the Laughlin, and a Laughlin quasiparticle many-body state. The
adiabatic following of the center of mass movement by the lowest energy dressed
internal state, is lost by the mixing of the second internal state. This
mixture can be controlled by the intensity of the laser field. The
non-adiabaticity is inherent to the considered setup, and is shown to play the
role of circular asymmetry. We study its influence on the properties of the
ground state of the system. Its main effect is to reduce the overlap of the
numerical solutions with the analytical trial expressions by occupying states
with higher angular momentum. Thus, we propose generalized wave functions
arising from the Laughlin and Pfaffian wave function by including components,
where extra Jastrow factors appear, while preserving important features of
these states. We analyze quasihole excitations over the Laughlin and
generalized Laughlin states, and show that they possess effective fractional
charge and obey anyonic statistics. Finally, we study the energy gap over the
Laughlin state as the number of particles is increased keeping the chemical
potential fixed. The gap is found to decrease as the number of particles is
increased, indicating that the observability of the Laughlin state is
restricted to a small number of particles.Comment: 28 pages, 16 figure
Tunnelling rates for the nonlinear Wannier-Stark problem
We present a method to numerically compute accurate tunnelling rates for a
Bose-Einstein condensate which is described by the nonlinear Gross-Pitaevskii
equation. Our method is based on a sophisticated real-time integration of the
complex-scaled Gross-Pitaevskii equation, and it is capable of finding the
stationary eigenvalues for the Wannier-Stark problem. We show that even weak
nonlinearities have significant effects in the vicinity of very sensitive
resonant tunnelling peaks, which occur in the rates as a function of the Stark
field amplitude. The mean-field interaction induces a broadening and a shift of
the peaks, and the latter is explained by analytic perturbation theory