arXiv subjects

Y. -J. Lin

Publications and source records attributed to Y. -J. Lin.

10 recordsLinked to original sources

arXiv2026

Realization of a Synthetic Hall Torus with a Spinor Bose-Einstein Condensate

We report the first experimental realization of a synthetic Hall torus using a spinor Bose-Einstein condensate confined in a ring-shaped trap with in situ imaging. By cyclically coupling three hyperfine spin states via Raman and microwave fields, we impose a periodic boundary condition in the synthetic dimension, which together with a real-space ring trap, realizes a toroidal geometry with a synthetic magnetic flux. This flux induces azimuthal density modulations in the condensate, whose periodicity is uniquely determined by the quantized toroidal magnetic flux-a hallmark of the Hall torus geometry. By varying the relative phase between the couplings across repeated experimental runs, we control the location of the density extrema, emulating the behavior of Thouless charge pump in a toroidal geometry. We further investigate the onset of these modulations as the system transitions from a cylindrical to a toroidal topology. Our results establish a versatile platform for investigating quantum Hall physics and topological phenomena in synthetic curved spaces.

cond-mat.quant-gas↗

arXiv2024

Vortex nucleations in spinor Bose condensates under localized synthetic magnetic fields

Gauge fields are ubiquitous in modern quantum physics. In superfluids, quantized vortices can be induced by gauge fields. Here we demonstrate the first experimental observation of vortex nucleations in light-dressed spinor Bose-Einstein condensates under radially-localized synthetic magnetic fields. The light-induced spin-orbital-angular-momentum coupling creates azimuthal gauge potentials $\vec{A}$ for the lowest-energy spinor branch dressed eigenstate. The observation of the atomic wave function in the lowest-energy dressed eigenstate reveals that vortices nucleate from the cloud center of a vortex-free state with canonical momentum $\vec{p} = 0$. This is because a large circulating azimuthal velocity field $\propto \vec{p}-\vec{A}$ at the condensate center results in a dynamically unstable localized excitation that initiates vortex nucleations. Furthermore, the long-time dynamics to reach the ground state stops in a metastable state when $|\vec{A}|$ is not sufficiently large. Our observation has reasonable agreement with the time-dependent Gross-Pitaevskii simulations.

cond-mat.quant-gas↗

arXiv2020

Visible stripe phases in spin-orbital-angular-momentum coupled Bose-Einstein condensates

Recently, stripe phases in spin-orbit coupled Bose-Einstein condensates (BECs) have attracted much attention since they are identified as supersolid phases. In this paper, we exploit experimentally reachable parameters and show theoretically that annular stripe phases with large stripe spacing and high stripe contrast can be achieved in spin-orbital-angular-momentum coupled (SOAMC) BECs. In addition to using Gross-Pitaevskii numerical simulations, we develop a variational ansatz that captures the essential interaction effects to first order, which are not present in the ansatz employed in previous literature. Our work should open the possibility toward directly observing stripe phases in SOAMC BECs in experiments.

cond-mat.quant-gas↗

arXiv2018

Rotating atomic quantum gases with light-induced azimuthal gauge potentials and the observation of Hess-Fairbank effect

We demonstrate synthetic azimuthal gauge potentials for Bose-Einstein condensates from engineering atom-light couplings. The gauge potential is created by adiabatically loading the condensate into the lowest energy Raman-dressed state, achieving a coreless vortex state. The azimuthal gauge potentials act as effective rotations and are tunable by the Raman coupling and detuning. We characterize the spin textures of the dressed states, in agreements with the theory. The lowest energy dressed state is stable with a 4.5-s half-atom-number-fraction lifetime. In addition, we exploit the azimuthal gauge potential to demonstrate the Hess-Fairbank effect, the analogue of Meissner effect in superconductors. The atoms in the absolute ground state has a zero quasi-angular momentum and transits into a polar-core vortex when the synthetic magnetic flux is tuned to exceed a critical value. Our demonstration serves as a paradigm to create topological excitations by tailoring atom-light interactions where both types of SO(3) vortices in the $|\langle \vec{F}\rangle|=1$ manifold, coreless vortices and polar-core vortices, are created in our experiment. The gauge field in the stationary Hamiltonian opens a path to investigating rotation properties of atomic superfluids under thermal equilibrium.

cond-mat.quant-gas↗

arXiv2018

Spin-orbital-angular-momentum coupled Bose-Einstein condensates

We demonstrate coupling between the atomic spin and orbital-angular-momentum (OAM) of the atom's center-of-mass motion in a Bose-Einstein condensate (BEC). The coupling is induced by Raman-dressing lasers with a Laguerre-Gaussian beam, and creates coreless vortices in a $F=1$ $^{87}$Rb spinor BEC. We observe correlations between spin and OAM in the dressed state and characterize the spin texture; the result is in good agreement with the theory. In the presence of the Raman field our dressed state is stable for 0.1~s or longer, and it decays due to collision-induced relaxation. As we turn off the Raman beams, the vortex cores in the bare spin $|m_F=1\rangle$ and $|-1\rangle$ split. These spin-OAM coupled systems with the Raman-dressing approach have great potential for exploring new topological textures and quantum states.

cond-mat.quant-gas↗

arXiv2012

Dynamically Slowed Collapse of a Bose-Einstein Condensate with Negative Scattering Length

We rapidly change the scattering length a_s of a 87Rb Bose-Einstein condensate by means of a Feshbach resonance, simultaneously releasing the condensate from its harmonic trapping potential. When a_s is changed from positive to negative, the subsequent collapse of the condensate is stabilized by the kinetic energy imparted during the release, resulting in a deceleration of the loss rate near the resonance. We also observe an increase in the Thomas-Fermi radius, near the resonance, that cannot be understood in terms of a simple scaling model. Instead, we describe this behavior using the Gross-Pitaevskii equation, including three-body recombination, and hypothesize that the increase in cloud radius is due to the formation of concentric shells.

cond-mat.quant-gas↗

arXiv2011

A spin-orbit coupled Bose-Einstein condensate

Spin-orbit (SO) coupling -- the interaction between a quantum particle's spin and its momentum -- is ubiquitous in nature, from atoms to solids. In condensed matter systems, SO coupling is crucial for the spin-Hall effect and topological insulators, which are of extensive interest; it contributes to the electronic properties of materials such as GaAs, and is important for spintronic devices. Ultracold atoms, quantum many-body systems under precise experimental control, would seem to be an ideal platform to study these fascinating SO coupled systems. While an atom's intrinsic SO coupling affects its electronic structure, it does not lead to coupling between the spin and the center-of-mass motion of the atom. Here, we engineer SO coupling (with equal Rashba and Dresselhaus strengths) in a neutral atomic Bose-Einstein condensate by dressing two atomic spin states with a pair of lasers. Not only is this the first SO coupling realized in ultracold atomic gases, it is also the first ever for bosons. Furthermore, in the presence of the laser coupling, the interactions between the two dressed atomic spin states are modified, driving a quantum phase transition from a spatially spin-mixed state (lasers off) to a phase separated state (above a critical laser intensity). The location of this transition is in quantitative agreement with our theory. This SO coupling -- equally applicable for bosons and fermions -- sets the stage to realize topological insulators in fermionic neutral atom systems.

cond-mat.quant-gas↗

arXiv2010

Phases of a 2D Bose Gas in an Optical Lattice

Ultra-cold atoms in optical lattices realize simple, fundamental models in condensed matter physics. Our 87Rb Bose-Einstein condensate is confined in a harmonic trapping potential to which we add an optical lattice potential. Here we realize the 2D Bose-Hubbard Hamiltonian and focus on the effects of the harmonic trap, not present in bulk condensed matter systems. By measuring condensate fraction we identify the transition from superfluid to Mott insulator as a function of atom density and lattice depth. Our results are in excellent agreement with the quantum Monte Carlo universal state diagram, suitable for trapped systems, introduced by Rigol et al. (Phys. Rev. A 79, 053605 (2009)).

cond-mat.quant-gas↗

arXiv2009

Rapid production of $^{87}$Rb BECs in a combined magnetic and optical potential

We describe an apparatus for quickly and simply producing $\Rb87$ Bose-Einstein condensates. It is based on a magnetic quadrupole trap and a red detuned optical dipole trap. We collect atoms in a magneto-optical trap (MOT) and then capture the atom in a magnetic quadrupole trap and force rf evaporation. We then transfer the resulting cold, dense cloud into a spatially mode-matched optical dipole trap by lowering the quadrupole field gradient to below gravity. This technique combines the efficient capture of atoms from a MOT into a magnetic trap with the rapid evaporation of optical dipole traps; the approach is insensitive to the peak quadrupole gradient and the precise trapping beam waist. Our system reliably produces a condensate with $N\approx2\times10^6$ atoms every $16\second$.

cond-mat.quant-gas↗

arXiv2008

A Bose-Einstein Condensate in a Uniform Light-induced Vector Potential

We use a two-photon dressing field to create an effective vector gauge potential for Bose-condensed Rb atoms in the F=1 hyperfine ground state. The dressed states in this Raman field are spin and momentum superpositions, and we adiabatically load the atoms into the lowest energy dressed state. The effective Hamiltonian of these neutral atoms is like that of charged particles in a uniform magnetic vector potential, whose magnitude is set by the strength and detuning of Raman coupling. The spin and momentum decomposition of the dressed states reveals the strength of the effective vector potential, and our measurements agree quantitatively with a simple single-particle model. While the uniform effective vector potential described here corresponds to zero magnetic field, our technique can be extended to non-uniform vector potentials, giving non-zero effective magnetic fields.

cond-mat.other↗