arXiv subjects

Ruixiao Yao

Publications and source records attributed to Ruixiao Yao.

11 recordsLinked to original sources

arXiv2025

Measuring pair correlations in Bose and Fermi gases via atom-resolved microscopy

We demonstrate atom-resolved detection of itinerant bosonic $^{23}$Na and fermionic $^6$Li quantum gases, enabling the direct in situ measurement of interparticle correlations. In contrast to prior work on lattice-trapped gases, here we realize microscopy of quantum gases in the continuum. We reveal Bose-Einstein condensation with single-atom resolution, measure the enhancement of two-particle $g^{(2)}$ correlations of thermal bosons, and observe the suppression of $g^{(2)}$ for fermions; the Fermi or exchange hole. For strongly interacting Fermi gases confined to two dimensions, we directly observe non-local fermion pairs in the BEC-BCS crossover. We obtain the pairing gap, the pair size, and the short-range contact directly from the pair correlations. In situ thermometry is enabled via the fluctuation-dissipation theorem. Our technique opens the door to the atom-resolved study of strongly correlated quantum gases of bosons, fermions, and their mixtures.

cond-mat.quant-gas↗

arXiv2024

Observation of chiral edge transport in a rapidly-rotating quantum gas

The frictionless, directional propagation of particles at the boundary of topological materials is one of the most striking phenomena in transport. These chiral edge modes lie at the heart of the integer and fractional quantum Hall effects, and their extraordinary robustness against noise and disorder reflects the quantization of Hall conductivity in these systems. Despite their central importance, controllable injection of edge modes, and direct imaging of their propagation, structure, and dynamics, is challenging. Here, we demonstrate the distillation of individual chiral edge states in a rapidly-rotating bosonic superfluid confined by an optical boundary. Tuning the wall sharpness, we reveal the smooth crossover between soft wall behaviour in which the propagation speed is proportional to wall steepness, and the hard wall regime exhibiting chiral free particles. From the skipping motion of atoms along the boundary, we spectroscopically infer the energy gap between the ground and first excited edge bands, and reveal its evolution from the bulk Landau level splitting for a soft boundary, to the hard wall limit.

cond-mat.quant-gas↗

arXiv2023

Geometric squeezing of rotating quantum gases into the lowest Landau level

The simulation of quantum Hall physics with rotating quantum gases is witnessing a revival due to recent experimental advances that enabled the observation of a Bose-Einstein condensate entirely contained in its lowest kinetic energy state, i.e. the lowest Landau level. We theoretically describe this experimental result, and show that it can be interpreted as a squeezing of the geometric degree of freedom of the problem, the guiding center metric. This "geometric squeezing" offers an unprecedented experimental control over the quantum geometry in Landau-level analogues, and at the same time opens a realistic path towards achieving correlated quantum phases akin to quantum Hall states with neutral atoms.

cond-mat.quant-gas↗

arXiv2023

Probing quantum many-body correlations by universal ramping dynamics

Ramping a physical parameter is one of the most common experimental protocols in studying a quantum system, and ramping dynamics has been widely used in preparing a quantum state and probing physical properties. Here, we present a novel method of probing quantum many-body correlation by ramping dynamics. We ramp a Hamiltonian parameter to the same target value from different initial values and with different velocities, and we show that the first-order correction on the finite ramping velocity is universal and path-independent, revealing a novel quantum many-body correlation function of the equilibrium phases at the target values. We term this method as the non-adiabatic linear response since this is the leading order correction beyond the adiabatic limit. We demonstrate this method experimentally by studying the Bose-Hubbard model with ultracold atoms in three-dimensional optical lattices. Unlike the conventional linear response that reveals whether the quasi-particle dispersion of a quantum phase is gapped or gapless, this probe is more sensitive to whether the quasi-particle lifetime is long enough such that the quantum phase possesses a well-defined quasi-particle description. In the Bose-Hubbard model, this non-adiabatic linear response is significant in the quantum critical regime where well-defined quasi-particles are absent. And in contrast, this response is vanishingly small in both superfluid and Mott insulators which possess well-defined quasi-particles. Because our proposal uses the most common experimental protocol, we envision that our method can find broad applications in probing various quantum systems.

cond-mat.quant-gas↗

arXiv2021

Observation of many-body quantum phase transitions beyond the Kibble-Zurek mechanism

Quantum critical behavior of many-body phase transitions is one of the most fascinating yet challenging questions in quantum physics. Here, we improved the band-mapping method to investigate the quantum phase transition from superfluid to Mott insulators, and we observed the critical behaviors of quantum phase transitions in both dynamical steady-state-relaxation region and phase-oscillation region. Based on various observables, two different values for the same quantum critical parameter are observed. This result is beyond a universal-scaling-law description of quantum phase transitions known as the Kibble-Zurek mechanism, and suggests that multiple quantum critical mechanisms are competing in many-body quantum phase transition experiments in inhomogeneous systems.

quant-ph↗

arXiv2021

Many-body localization in tilted and harmonic potentials

We discuss nonergodic dynamics of interacting spinless fermions in a tilted optical lattice as modeled by XXZ spin chain in magnetic (or electric) field changing linearly across the chain. The time dynamics is studied using exact propagation for small chains and matrix product states techniques for larger system sizes. We consider both the initial Néel separable state as well as the quantum quench scenario in which the initial state may be significantly entangled. We show that the entanglement dynamics is significantly different in both cases. In the former a rapid initial growth is followed by a saturation for sufficiently large tilt, $F$. In the latter case the dynamics seems to be dominated by pair tunneling and the effective tunneling rate scales as $1/F^2$. In the presence of an additional harmonic potential the imbalance is found to be entirely determined by a local effective tilt, $F_{\text{loc}}$, the entanglement entropy growth is modulated with frequency that follows $1/F_{loc}^2$ scaling first but at long time the dynamics is determined rather by the curvature of the harmonic potential. Only for large tilts or sufficiently large curvatures, corresponding to the deeply localized regime, we find the logarithmic entanglement growth for Néel initial state. The same curvature determines long-time imbalance for large $F$ which reveals strong revival phenomena associated with the manifold of equally spaced states, degenerate in the absence of the harmonic potential.

cond-mat.dis-nn↗

arXiv2021

Nonergodic dynamics in disorder-free potentials

We review the dynamics of interacting particles in disorder-free potentials concentrating on a combination of a harmonic binding with a constant tilt. We show that a simple picture of an effective local tilt describes a variety of cases. Our examples include spinless fermions (as modeled by Heisenberg spin chain in a magnetic field), spinful fermions as well as bosons that enjoy a larger local on-site Hilbert space. We also discuss the domain-wall dynamics that reveals nonergodic features even for a relatively weak tilt as suggested by Doggen et. al. [arXiv:2012.13722]. By adding a harmonic potential on top of the static field we confirm that the surprizing regular dynamics is not entirely due to Hilbert space shuttering. It seems better explained by the inhibited transport within the domains of identically oriented spins. Once the spin-1/2 restrictions are lifted as, e.g., for bosons, the dynamics involve stronger entanglement generation. Again for domain wall melting, the effect of the harmonic potential is shown to lead mainly to an effective local tilt.

cond-mat.dis-nn↗

arXiv2020

Many-body localization of bosons in optical lattice: Dynamics in disorder-free potentials

The phenomenon of Many-Body Stark Localization of bosons in tilted optical lattice is studied. Despite the fact that no disorder is necessary for Stark localization to occur, it is very similar to well known many body localization (MBL) in sufficiently strong disorder. Not only the mean gap ratio reaches poissonian value as characteristic for localized situations but also the eigenstates reveal multifractal character as in standard MBL. Stark localization enables a coexistence of spacially separated thermal and localized phases in the harmonic trap similarly to fermions. Stark localization may also lead to spectacular trapping of particles in a reversed harmonic field which naively might be considered as an unstable configuration.

cond-mat.quant-gas↗

arXiv2020

Coexistence of localized and extended phases: Many-body localization in a harmonic trap

We show that the presence of a harmonic trap may in itself lead to many-body localization for cold atoms confined in that trap in a quasi-one-dimensional geometry. Specifically, the coexistence of delocalized phase in the center of the trap with localized region closer to the edges is predicted with the borderline dependent on the curvature of the trap. The phenomenon, similar in its origin to Stark localization, should be directly observed with cold atomic species. We discuss both the spinless and the spinful fermions, for the latter we address Stark localization at the same time as it has not been analyzed up till now.

cond-mat.stat-mech↗

arXiv2020

Many-body localization in Bose-Hubbard model: evidence for the mobility edge

Motivated by recent experiments on interacting bosons in quasi-one-dimensional optical lattice [Nature {\bf 573}, 385 (2019)] we analyse theoretically properties of the system in the crossover between delocalized and localized regimes. Comparison of time dynamics for uniform and density wave like initial states enables demonstration of the existence of the mobility edge. To this end we define a new observable, the mean speed of transport at long times. It gives us an efficient estimate of the critical disorder for the crossover. We also show that the mean velocity growth of occupation fluctuations close to the edges of the system carries the similar information. Using the quantum quench procedure we show that it is possible to probe the mobility edge for different energies.

cond-mat.dis-nn↗

arXiv2020

Dimension Crossing Turbulent Cascade in an Excited Lattice Bose Gas

Turbulence is an intriguing non-equilibrium state, which originates from fluid mechanics and has far-reaching consequences in the description of climate physics, the characterization of quantum hydrodynamics, and the understanding of cosmic evolution. The concept of turbulent cascade describing the energy redistribution across different length scales offers one profound route to reconcile fundamental conservative forces with observational energy non-conservation of accelerating expansion of the universe bypassing the cosmological constant. Here, we observe a dimension crossing turbulent energy cascade in an atomic Bose-Einstein condensate confined in a two-dimensional (2d) optical lattice forming a 2d array of tubes, which exhibits universal behaviors in the dynamical energy-redistribution across different dimensions. By exciting atoms into the optical-lattice high bands, the excessive energy of this quantum many-body system is found to cascade from the transverse two-dimensional lattice directions to the continuous dimension, giving rise to a one-dimensional turbulent energy cascade, which is in general challenging to reach due to integrability. We expect this observed novel phenomenon of dimension-crossing energy cascade may inspire microscopic theories for modeling positive cosmological constant of our inflationary universe.

cond-mat.quant-gas↗