arXiv subjects

Wei Yi

Publications and source records attributed to Wei Yi.

At least 145 records · Page 8Linked to original sources

arXiv2018

Parametric resonance of a Bose-Einstein condensate in a ring trap with periodically driven interactions

We study the instability of a ring Bose-Einstein condensate under a periodic modulation of inter-atomic interactions. The condensate exhibits temporal and spatial patterns induced by the parametric resonance, which can be characterized by Bogoliubov quasi-particle excitations in the Floquet basis. As the ring geometry significantly limits the number of excitable Bogoliubov modes, we are able to capture the non-linear dynamics of the condensate using a three-mode model. We further demonstrate the robustness of the temporal and spatial patterns against disorder, which are attributed to the mode-locking mechanism under the ring geometry. Our results can be observed in cold atomic systems and are also relevant to physical systems described by the non-linear Schrodinger's equation.

cond-mat.quant-gas↗

arXiv2018

Universal relations and normal phase of an ultracold Fermi gas with coexisting $s$- and $p$-wave interactions

We study the universal relations and normal-phase thermodynamics of a two-component ultracold Fermi gas with coexisting $s$- and $p$-wave interactions. Due to the orthogonality of two-body wave functions of different scattering channels, the universal thermodynamic relations of the system appear to be direct summations of contributions from each partial-wave scattering channels. These universal relations are dictated by a set of contacts, which can be associated with either $s$- or $p$-wave interactions. Interestingly, due to the interplay of $s$- and $p$-wave interactions on the many-body level, the contacts, and hence all the relevant thermodynamic quantities, behave differently from those with only $s$- or $p$-wave interactions. These are manifest in our numerical calculations based on second-order virial expansions for $^{40}$K atoms under typical experimental parameters. A particularly interesting finding is that, due to the coexistence of $s$- and $p$-wave scatterings, the interaction energy of the repulsive branch features abrupt changes across the $p$-wave resonances. Our results can be readily checked experimentally for $^{40}$K atoms near the $198$G $p$-wave Feshbach resonance, where multiple partial-wave scatterings naturally coexist.

cond-mat.quant-gas↗

arXiv2018

Magnetic orders in a Fermi gas induced by cavity-field fluctuations

We study magnetic orders of fermions under cavity-assisted Raman couplings in a one-dimensional lattice at half filling. The cavity-enhanced atom-photon coupling introduces a dynamic long-range interaction between the fermions, which competes with the short-range on-site interaction and leads to a variety of magnetic orders. Adopting a numerical density-matrix-renormalization-group method, we investigate the various magnetic orders and map out the steady-state phase diagram. Interestingly, as all the phase transitions take place outside the superradiant regime, the magnetic orders are associated with cavity-field fluctuations with a vanishing number of photons on the mean-field level.

quant-ph↗

arXiv2017

Tuning Feshbach resonance in cold atomic gases with inter-channel coupling

We show that the essential properties of a Feshbach resonance in cold atomic gases can be tuned by dressing the atomic states in different scattering channels through inter-channel couplings. Such a scheme can be readily implemented in the orbital Feshbach resonance of alkaline-earth-like atoms by coupling hyperfine states in the clock-state manifolds. Using $^{173}$Yb atoms as an example, we find that both the resonance position and the two-body bound-state energy depend sensitively on the inter-channel coupling strength, which offers control parameters in tuning the inter-atomic interactions. We also demonstrate the dramatic impact of the dressed Feshbach resonance on many-body processes such as the polaron to molecule transition and the BCS-BEC crossover.

cond-mat.quant-gas↗

arXiv2017

Symmetry-protected topological states for interacting fermions in alkaline-earth-like atoms

We discuss the quantum simulation of symmetry-protected topological (SPT) states for interacting fermions in quasi-one-dimensional gases of alkaline-earth-like atoms such as $^{173}$Yb. Taking advantage of the separation of orbital and nuclear-spin degrees of freedom in these atoms, we consider Raman-assisted spin-orbit couplings in the clock states, which, together with the spin-exchange interactions in the clock-state manifolds, give rise to SPT states for interacting fermions. We numerically investigate the phase diagram of the system, and study the phase transitions between the SPT phase and the symmetry-breaking phases. The interaction-driven topological phase transition can be probed by measuring local density distribution of the topological edge modes.

cond-mat.quant-gas↗

arXiv2017

Repulsive polarons in alkaline-earth(-like) atoms across an orbital Feshbach resonance

We characterize properties of the so-called repulsive polaron across the recently discovered orbital Feshbach resonance in alkaline-earth(-like) atoms. Being a metastable quasiparticle excitation at the positive energy, the repulsive polaron is induced by the interaction between an impurity atom and a Fermi sea. By analyzing in detail the energy, the polaron residue, the effective mass, and the decay rate of the repulsive polaron, we reveal interesting features that are intimately related to the two-channel nature of the orbital Feshbach resonance. In particular, we find that the life time of the repulsive polaron is non-monotonic in the Zeeman-field detuning bewteen the two channels, and has a maximum on the BEC-side of the resonance. Further, by considering the stability of a mixture of the impurity and the majority atoms against phase separation, we show that the itin- erant ferromagnetism may exist near the orbital Feshbach resonance at appropriate densities. Our results can be readily probed experimentally, and have interesting implications for the observation of itinerant ferromagnetism near an orbital Feshbach resonance.

cond-mat.quant-gas↗

arXiv2017

Interaction-modulated tunneling dynamics in a mixture of Bose-Einstein condensates

We study the interaction-modulated tunneling dynamics of a Bose-Einstein condensate (BEC) in a deep double-well potential, where the tunneling between the two wells is modulated by another BEC trapped in a harmonic potential symmetrically positioned at the center of the double-well potential. The inter-species interactions couple the dynamics of the two BECs, which give rise to interesting features in the tunneling oscillations. Adopting a two-mode approximation for the BEC in the double-well potential and coupling it with the Gross-Pitaevskii equation of the harmonically trapped BEC, we numerically investigate the coupled dynamics of the BEC mixture, and map out the phase diagram of the tunneling dynamics. We show that the dynamical back action of the BEC in the harmonic trap leads to strong non-linearity in the oscillations of the BEC in the double-well potential, which enriches the system dynamics, and enhances macroscopic self trapping. The transition between the Josephson oscillation and the self-trapping dynamics can be identified by monitoring the oscillation frequency of the double-well BEC. Our results suggest the possibility of tuning the tunneling dynamics of BECs in double-well potentials.

cond-mat.quant-gas↗

arXiv2017

Multi-object Tracking for Generic Observation Model Using Labeled Random Finite Sets

This paper presents an exact Bayesian filtering solution for the multi-object tracking problem with the generic observation model. The proposed solution is designed in the labeled random finite set framework, using the product styled representation of labeled multi-object densities, with the standard multi-object transition kernel and no particular simplifying assumptions on the multi-object likelihood. Computationally tractable solutions are also devised by applying a principled approximation involving the replacement of the full multi-object density with a labeled multi-Bernoulli density that minimizes the Kullback-Leibler divergence and preserves the first-order moment. To achieve the fast performance, a dynamic grouping procedure based implementation is presented with a step-by-step algorithm. The performance of the proposed filter and its tractable implementations are verified and compared with the state-of-the-art in numerical experiments.

eess.SY↗

arXiv2017

Robust Distributed Fusion with Labeled Random Finite Sets

This paper considers the problem of the distributed fusion of multi-object posteriors in the labeled random finite set filtering framework, using Generalized Covariance Intersection (GCI) method. Our analysis shows that GCI fusion with labeled multi-object densities strongly relies on label consistencies between local multi-object posteriors at different sensor nodes, and hence suffers from a severe performance degradation when perfect label consistencies are violated. Moreover, we mathematically analyze this phenomenon from the perspective of Principle of Minimum Discrimination Information and the so called yes-object probability. Inspired by the analysis, we propose a novel and general solution for the distributed fusion with labeled multi-object densities that is robust to label inconsistencies between sensors. Specifically, the labeled multi-object posteriors are firstly marginalized to their unlabeled posteriors which are then fused using GCI method. We also introduce a principled method to construct the labeled fused density and produce tracks formally. Based on the developed theoretical framework, we present tractable algorithms for the family of generalized labeled multi-Bernoulli (GLMB) filters including $δ$-GLMB, marginalized $δ$-GLMB and labeled multi-Bernoulli filters. The robustness and efficiency of the proposed distributed fusion algorithm are demonstrated in challenging tracking scenarios via numerical experiments.

eess.SY↗

arXiv2017

Detecting topological invariants in nonunitary discrete-time quantum walks

We report the experimental detection of bulk topological invariants in nonunitary discrete-time quantum walks with single photons. The nonunitarity of the quantum dynamics is enforced by periodically performing partial measurements on the polarization of the walker photon, which effectively introduces loss to the dynamics. The topological invariant of the nonunitary quantum walk is manifested in the quantized average displacement of the walker, which is probed by monitoring the photon loss. We confirm the topological properties of the system by observing localized edge states at the boundary of regions with different topological invariants. We further demonstrate the robustness of both the topological properties and the measurement scheme of the topological invariants against disorder.

quant-ph↗

arXiv2017

Pressure-induced melting of magnetic order and emergence of new quantum state in alpha-RuCl3

Here we report the observation of pressure-induced melting of antiferromagnetic (AFM) order and emergence of a new quantum state in the honeycomb-lattice halide alpha-RuCl3, a candidate compound in the proximity of quantum spin liquid state. Our high-pressure heat capacity measurements demonstrate that the AFM order smoothly melts away at a critical pressure (Pc) of 0.7 GPa. Intriguingly, the AFM transition temperature displays an increase upon applying pressure below the Pc, in stark contrast to usual phase diagrams, for example in pressurized parent compounds of unconventional superconductors. Furthermore, in the high-pressure phase an unusual steady of magnetoresistance is observed. These observations suggest that the high-pressure phase is in an exotic gapped quantum state which is robust against pressure up to ~140 GPa.

cond-mat.str-el↗

arXiv2017

$h/e$ superconducting quantum interference through trivial edge states in InAs

Josephson junctions defined in strong spin orbit semiconductors are highly interesting for the search for topological systems. However, next to topological edge states that emerge in a sufficient magnetic field, trivial edge states can also occur. We study the trivial edge states with superconducting quantum interference measurements on non-topological InAs Josephson junctions. We observe a SQUID pattern, an indication of superconducting edge transport. Also, a remarkable $h/e$ SQUID signal is observed that, as we find, stems from crossed Andreev states.

cond-mat.mes-hall↗

arXiv2017

Interaction-induced exotic vortex states in an optical lattice clock with spin-orbit coupling

Motivated by a recent experiment [L. F. Livi, et al., Phys. Rev. Lett. 117, 220401(2016)], we study the ground-state properties of interacting fermions in a one-dimensional optical lattice clock with spin-orbit coupling. As the electronic and the hyperfine-spin states in the clock-state manifolds can be treated as effective sites along distinct synthetic dimensions, the system can be considered as multiple two-leg ladders with uniform magnetic flux penetrating the plaquettes of each ladder. As the inter-orbital spin-exchange interactions in the clock-state manifolds couple individual ladders together, we show that exotic interaction-induced vortex states emerge in the coupled-ladder system, which compete with existing phases of decoupled ladders and lead to a rich phase diagram. Adopting the density matrix renormalization group approach, we map out the phase diagram, and investigate in detail the currents and the density-density correlations of the various phases. Our results reveal the impact of interactions on spin-orbit coupled systems, and are particularly relevant to the on-going exploration of spin-orbit coupled optical lattice clocks.

cond-mat.quant-gas↗

arXiv2017

Topological superradiant state in Fermi gases with cavity induced spin-orbit coupling

Coherently driven atomic gases inside optical cavities hold great promise for generating rich dynamics and exotic states of matter. It was shown recently that an exotic topological superradiant state exists in a two-component degenerate Fermi gas coupled to a cavity, where local order parameters coexist with global topological invariants. In this work, we characterize in detail various properties of this exotic state, focusing on the feedback interactions between the atoms and the cavity field. In particular, we demonstrate that cavity-induced interband coupling plays a crucial role in inducing the topological phase transition between the conventional and topological superradiant states. We analyze the interesting signatures in the cavity field left by the closing and reopening of the atomic bulk gap across the topological phase boundary and discuss the robustness of the topological superradiant state by investigating the steady-state phase diagram under various conditions. Furthermore, we consider the interaction effect and discuss the interplay between the pairing order in atomic ensembles and the superradiance of the cavity mode. Our work provides many valuable insights into the unique cavity--atom hybrid system under study and is helpful for future experimental exploration of the topological superradiant state.

cond-mat.quant-gas↗

arXiv2017

Heavy fermion behavior in the quasi-one-dimensional Kondo lattice CeCo2Ga8

Dimensionality plays an essential role in determining the anomalous non-Fermi liquid properties in heavy fermion systems. So far most heavy fermion compounds are quasi-two-dimensional or three-dimensional. Here we report the synthesis and systematic investigations of the single crystals of the quasi-one-dimensional Kondo lattice CeCo$_2$Ga$_8$. Resistivity measurements at ambient pressure reveal the onset of coherence at $T^*\approx 20\,$K and non-Fermi liquid behavior with linear temperature dependence over a decade in temperature from 2 K to 0.1 K. The specific heat increases logarithmically with lowering temperature between 10 K and 2 K and reaches 800 mJ/mol K$^2$ at 1 K, suggesting that CeCo$_2$Ga$_8$ is a heavy fermion compound in the close vicinity of a quantum critical point. Resistivity measurements under pressure further confirm the non-Fermi liquid behavior in a large temperature-pressure range. The magnetic susceptibility is found to follow the typical behavior for a one-dimensional (1D) spin chain from 300 K down to $T^*$, and first-principles calculations predict flat Fermi surfaces for the itinerant $f$-electron bands. These suggest that CeCo$_2$Ga$_8$ is a rare example of the quasi-1D Kondo lattice, but its non-Fermi liquid behaviors resemble those of the quasi-two-dimensional YbRh$_2$Si$_2$ family. The study of the quasi-one-dimensional CeCo$_2$Ga$_8$ family may therefore help us to understand the role of dimensionality on heavy fermion physics and quantum criticality.

cond-mat.str-el↗

arXiv2017

Gapped spin-1/2 spinon excitations in a new kagome quantum spin liquid compound Cu$_3$Zn(OH)$_6$FBr

We report a new kagome quantum spin liquid candidate Cu$_3$Zn(OH)$_6$FBr, which does not experience any phase transition down to 50 mK, more than three orders lower than the antiferromagnetic Curie-Weiss temperature ($\sim$ 200 K). A clear gap opening at low temperature is observed in the uniform spin susceptibility obtained from $^{19}$F nuclear magnetic resonance measurements. We observe the characteristic magnetic field dependence of the gap as expected for fractionalized spin-1/2 spinon excitations. Our experimental results provide firm evidence for spin fractionalization in a topologically ordered spin system, resembling charge fractionalization in the fractional quantum Hall state.

cond-mat.str-el↗

arXiv2017

Vortex-core structure in a mixture of Bose and Fermi superfluids

We study a single quantized vortex in the fermionic component of a mixture of Fermi superfluid and Bose-Einstein condensate. As the density ratio between the boson and the fermion components is tuned, we identify a transition in the vortex-core structure, across which fermions in the vortex core become completely depleted even in the weak-coupling Bardeen-Cooper-Schrieffer regime. This is accompanied by changes in key properties of the vortex state, as well as by the localization of the Bose-Einstein condensate in the vortex core. The transition in the vortex-core structure can be experimentally probed in Bose-Fermi superfluid mixtures by detecting the size and visibility of the vortices.

cond-mat.quant-gas↗

arXiv2017

Topological Fulde-Ferrell states in alkaline-earth-metal-like atoms near an orbital Feshbach resonance

We study the effects of synthetic spin-orbit coupling on the pairing physics in quasi-one-dimensional ultracold Fermi gases of alkaline-earth-metal-like atoms near an orbital Feshbach resonance (OFR). The interplay between spin-orbit coupling and pairing interactions near the OFR leads to an interesting topological Fulde-Ferrell state, where the nontrivial topology of the state is solely encoded in the closed channel with a topologically trivial Fulde-Ferrell pairing in the open channel. We confirm the topological property of the system by characterizing the Zak phase and the edge states. The topological Fulde-Ferrell state can be identified by the momentum-space density distribution obtained from time-of-flight images.

cond-mat.quant-gas↗