arXiv subjects

Zhi-Fang Xu

Publications and source records attributed to Zhi-Fang Xu.

23 records · Page 2Linked to original sources

arXiv2015

Spontaneous quantum Hall effect in an atomic spinor Bose-Fermi mixture

We study a mixture of spin-$1$ bosonic and spin-$1/2$ fermionic cold atoms, e.g., $^{87}$Rb and $^{6}$Li, confined in a triangular optical lattice. With fermions at $3/4$ filling, Fermi surface nesting leads to spontaneous formation of various spin textures of bosons in the ground state, such as collinear, coplanar and even non-coplanar spin orders. The phase diagram is mapped out with varying boson tunneling and Bose-Fermi interactions. Most significantly, in one non-coplanar state the mixture is found to exhibit a spontaneous quantum Hall effect in fermions and crystalline superfluidity in bosons, both driven by interaction.

cond-mat.quant-gas↗

arXiv2015

Tunable spin-orbit coupling synthesized with a modulating gradient magnetic field

We report the observation of tunable spin-orbit coupling (SOC) for ultracold $^{87}$Rb atoms in hyperfine spin-1 states. Different from most earlier experiments where atomic SOC of pseudo-spin-1/2 are synthesized with Raman coupling lasers, the scheme we demonstrate employs a gradient magnetic field (GMF) with ground state atoms and is immune to atomic spontaneous emission. The effect of the SOC is confirmed through the studies of: 1) the collective dipole oscillation of an atomic condensate in a harmonic trap after the synthesized SOC is abruptly turned on; and 2) the minimum energy state at a finite adiabatically adjusted momentum when the SOC strength is slowly ramped up. The coherence properties of the spinor condensates remain very good after interacting with modulating GMFs, which prompts the enthusiastic claim that our work provides a new repertoire for synthesized gauge fields aimed at quantum simulation studies with cold atoms.

cond-mat.quant-gas↗

arXiv2015

Coherent heteronuclear spin dynamics in an ultracold spin-1 mixture

We report the observation of coherent heteronuclear spin dynamics driven by inter-species spin-spin interaction in an ultracold spinor mixture, which manifests as periodical and well correlated spin oscillations between two atomic species. In particular, we investigate the magnetic field dependence of the oscillations and find a resonance behavior which depends on {\em both} the linear and quadratic Zeeman effects and the spin-dependent interaction. We also demonstrate a unique knob for controlling the spin dynamics in the spinor mixture with species-dependent vector light shifts. Our finds are in agreement with theoretical simulations without any fitting parameters.

physics.atom-ph↗

arXiv2013

Atomic spin-orbit coupling synthesized with magnetic-field-gradient pulses

We discuss a general scheme for creating atomic spin-orbit coupling (SOC) such as the Rashba or Dresselhaus types using magnetic-field-gradient pulses. In contrast to conventional schemes based on adiabatic center-of-mass motion with atomic internal states restricted to a dressed-state subspace, our scheme works for the complete subspace of a hyperfine-spin manifold by utilizing the coupling between the atomic magnetic moment and external magnetic fields. A spatially dependent pulsed magnetic field acts as an internal-state-dependent impulse, thereby coupling the atomic internal spin with its orbital center-of-mass motion, as in the Einstein-de Haas effect. This effective coupling can be dynamically manipulated to synthesize SOC of any type (Rashba, Dresselhaus, or any linear combination thereof). Our scheme can be realized with most experimental setups of ultracold atoms and is especially suited for atoms with zero nuclear spins.

cond-mat.quant-gas↗

arXiv2013

Gauge-spin-space rotation invariant vortices in spin-orbit coupled Bose-Einstein condensates

We revisit ground states of spinor Bose-Einstein condensates with a Rashba spin-orbit coupling, and find that votices show up as a direct consequence of spontaneous symmetry breaking into a combined gauge, spin, and space rotation symmetry, which determines the vortex-core spin state at the rotating center. For the continuous combined symmetry, the total spin rotation about the rotating axis is restricted to $2π$, whereas for the discrete combined symmetry, we further need 2F quantum numbers to characterize the total spin rotation for the spin-$F$ system. For lattice phases we find that in the ground state the topological charge for each unit cell vanishes. However, we find two types of highly symmetric lattices with a nontrivial topological charge in the spin-$\frac{1}{2}$ system based on the symmetry classification, and show that they are skyrmion crystals.

cond-mat.quant-gas↗