arXiv subjects

Yanliang Guo

Publications and source records attributed to Yanliang Guo.

18 recordsLinked to original sources

arXiv2026

Precision tests of nonlinear and stochastic modifications of quantum mechanics with a 1D quantum gas

We propose a cold-atom platform for precision tests of nonlinear and stochastic modifications to the Schr\"odinger equation, utilizing strongly correlated ultracold $^{133}$Cs in a uniform array of one-dimensional tubes formed by a two-dimensional optical lattice. Objective collapse models can be tested using the metastable super-Tonks-Girardeau gas. Based on a calibration test performed on our existing experimental setup, we project a sensitivity to the Continuous Spontaneous Localization collapse rate of $\lambda_c \simeq 1.8\times10^{-11}\,\mathrm{s^{-1}}$ at a correlation length of $r_c = 10^{-7}\,$m. This would establish a new bound an order of magnitude below the strongest existing constraint that remains robust against a cutoff in the collapse noise spectrum. Additionally, we can test deterministic nonlinear modifications by probing the symmetry-protected breathing mode frequency of the Tonks-Girardeau gas in harmonic traps. Crucial to both measurement schemes is the capability to independently tune the atom number and the linear density. By exploiting the different scaling laws associated with these parameters, we can cleanly distinguish genuine new physics signals from technical systematics.

cond-mat.quant-gas↗

arXiv2026

Observing the emergence of a velocity hierarchy in matter waves

Classical waves in dispersive media naturally exhibit distinct phase and group velocities. Whether an analogous separation of velocities can emerge in matter waves under strong many-body interactions has remained experimentally unexplored. Here, we demonstrate the emergence of a velocity hierarchy in a strongly interacting lattice gas. Using quench spectroscopy together with time-resolved correlation measurements, we independently determine the sound, group, and phase velocities across the superfluid-to-Mott-insulator transition. These velocities are nearly degenerate close to the transition, but progressively separate as the Mott gap opens and the quasiparticle dispersion acquires a massive relativistic-like form. Strikingly, phase-coherence fronts propagate faster than the Lieb-Robinson velocity scale while remaining fully consistent with locality. The measured velocities satisfy a relativistic-like invariance relation in the insulating regime. Our results establish propagation-velocity hierarchies as emergent signatures of strongly correlated quantum dynamics.

cond-mat.quant-gas↗

arXiv2026

Interaction-enabled metal-insulator phase transition in a driven quantum gas

Particle transport and energy flow are central to a wide range of phenomena in the natural sciences. While interactions generically promote ergodicity and diffusion, quantum interference can arrest transport, defying classical expectations. Here, we experimentally investigate their interplay in a periodically driven 3D quantum gas with tunable interactions. Strikingly, we find a sharp dynamical boundary separating localization from diffusive energy absorption. By tuning the driving amplitude and interaction strength, we map the localization-delocalization phase diagram and characterize this boundary via finite-time scaling. On the insulating side, we observe many-body dynamical localization (MBDL) featuring arrested momentum-space transport. Transport becomes subdiffusive near the boundary and diffusive in the delocalized regime, yielding a metal-insulator transition that we interpret as localization in many-body Hilbert space. Our results exemplify an interaction-enabled dynamical phase transition in a closed Floquet many-body system, and clarify how coherence and interactions jointly govern the quantum-to-classical transition.

cond-mat.quant-gas↗

arXiv2026

The wave nature of a Mott insulator

Quantum phases of matter are routinely identified by coherence features, with interference patterns being one of the most directly observable quantities. In lattices, the superfluid-to-Mott-insulator (SF-MI) transition is commonly viewed as a change from wave-like coherence to particle-like localization: interference peaks are taken as a hallmark of superfluidity, whereas their disappearance is used to diagnose insulating behavior. Here, we challenge this picture for one-dimensional (1D) strongly interacting gases subject to a lattice potential. We realize a gapped Mott insulator through pinning in a shallow lattice and find that pronounced interference peaks persist deep in the insulating regime. Strikingly, the interference becomes stronger as the Mott fraction increases, demonstrating that a certain degree of coherence still exists in the insulator state. Measurements of the one-body correlation function reveal an oscillatory, exponentially decaying coherence pattern across several lattice sites, in quantitative agreement with quantum Monte Carlo (QMC) simulations. Our work shows that interference does not uniquely diagnose superfluidity and it exposes the unexpected wave nature of a 1D Mott insulator.

cond-mat.quant-gas↗

arXiv2026

Realization of fractional Fermi seas

The Pauli exclusion principle is a cornerstone of quantum physics: it governs the structure of matter. Extensions of this principle, such as Haldane's generalized exclusion statistics, predict the existence of exotic quantum states characterized by fractional Fermi seas (FFS), i.e. momentum distributions with uniform but fractional occupancies. Here, we report the experimental realization of fractional Fermi seas in an excited one-dimensional Bose gas prepared through ramping cycles in the interaction strength. The resulting excited yet stable Bose-gas states exhibit Friedel oscillations, smoking-gun signatures of the underlying FFS. The stabilization of these states offers an opportunity to deepen our understanding of quantum thermodynamics in the presence of exotic statistics and paves the way for applications in quantum information and sensing.

cond-mat.quant-gas↗

arXiv2026

Exotic critical states as fractional Fermi seas in the one-dimensional Bose gas

Critical quantum field theories occupy a central position in modern theoretical physics for their inherent universality stemming from long-range correlations. As an example, the Tomonaga-Luttinger liquid (TLL) describes a wealth of one-dimensional quantum systems at low temperatures. Its behavior is deeply rooted in the emergence of an effective Fermi sea, leading to power-law correlations and Friedel oscillations. A promising direction to realize systems exhibiting novel universal behavior beyond TLL is through the generalization of the underlying Fermi sea. In this Letter, we show that fractional Fermi seas with reduced occupancy arise in an integrable Bose gas driven out of equilibrium by cyclic changes in interactions from repulsive to attractive. The correlation functions feature signatures of criticality incompatible with a conventional TLL, suggesting a novel critical phase. Our predictions, based on Generalized Hydrodynamics, are directly relevant to cold atoms.

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arXiv2026

Observing dissipationless flow of an impurity in a strongly repulsive quantum fluid

The frictionless motion of an object through a fluid medium is commonly viewed as a hallmark of superfluidity. According to Landau, kinematic constraints prohibit superfluid behavior in one-dimensional (1D) bosonic systems. Here, using ultracold atoms, we show how a microscopic impurity can propagate through a strongly interacting 1D Bose gas without any friction, at odds with conventional expectations. We inject the impurity with initial velocities ranging from the subsonic to supersonic regime, and subsequently track its dynamics. For supersonic initial velocities, we observe the formation of a shock wave and a remarkably fast relaxation to a stationary regime, on a time scale that increases with decreasing impurity velocity. After reaching the stationary state, the impurity continues its motion through the system with a finite velocity. Our findings demonstrate how quantum effects can conspire to eliminate dissipation of a microscopic object immersed in a quantum fluid, thereby bringing novel insights into the propagation of matter and information in the quantum realm.

cond-mat.quant-gas↗

arXiv2025

Observing Bethe strings in an attractive Bose gas far from equilibrium

Bethe strings are bound states of constituent particles in a variety of interacting many-body one-dimensional (1D) integrable quantum models relevant to magnetism, nanophysics, cold atoms and beyond. As emergent fundamental excitations, they are predicted to collectively reshape observable equilibrium and dynamical properties. Small individual Bethe strings have recently been observed in quantum magnets and superconducting qubits. However, creating states featuring intermixtures of many, including large, strings remains an outstanding experimental challenge. Here, using nearly integrable ultracold Bose gases, we realize such intermixtures of Bethe strings out of equilibrium, by dynamically tuning interactions from repulsive to attractive. We measure the average binding energy of the strings, revealing the presence of bound states of more than six particles. We find further evidence for them in the momentum distribution and in Tan's contact, connected to the correlated density. Our data quantitatively agree with predictions from generalized hydrodynamics (GHD). Manipulating intermixtures of Bethe strings opens new avenues for understanding quantum coherence, nonlinear dynamics and thermalization in strongly-interacting 1D systems.

cond-mat.quant-gas↗

arXiv2025

Anyonization of bosons in one dimension: an effective swap model

Anyons emerge as elementary excitations in low-dimensional quantum systems and exhibit behavior distinct from bosons or fermions. Previous models of anyons in one dimension (1D) are mainly categorized into two types: those that rely on nontrivial scattering behavior, and those based on density-dependent hopping processes in discrete lattices. Here, we introduce a novel framework for realizing anyonic correlations using the internal degrees of freedom of a spinor quantum gas. We propose a "swap" model, which assigns a complex phase factor to the swapping processes between two different species, referred to as "host particles" and "impurities". The anyonic characteristics are demonstrated through the one-body correlator of the impurity, using a spin-charge separation analysis. For a single impurity, our swap model can be effectively implemented by applying tilt potentials in a strongly interacting quantum gas [Dhar et al., arXiv:2412.21131]. We further explore the dynamical properties of anyonic correlations and extend our analysis to the case of multiple impurities. Our work provides new avenues for engineering many-body anyonic behavior in quantum simulation platforms.

cond-mat.quant-gas↗

arXiv2025

Origin and emergent features of many-body dynamical localization

The question of whether interactions can break dynamical localization in quantum kicked rotor systems has been the subject of a long--standing debate. Here, we introduce an extended mapping from the kicked Lieb--Liniger model to a high--dimensional lattice model and reveal universal features: on--site pseudorandomness and hybrid exponential--algebraic decay couplings with increasing momenta. We find that the exponent and the amplitude of the algebraic decay undergo a crossover as the interaction strength increases. This mapping uncovers the origin of dynamical localization and the interaction effect on the integrability of the system. An analysis of the generalized fractal dimension and level--spacing ratio supports these findings, highlighting the presence of near integrability and multifractality in different regions of parameter space. Our results offer an explanation for the occurrence of many--body dynamical localization, particularly in strongly correlated quantum gases, and are anticipated to generalize to systems of many particles.

cond-mat.quant-gas↗

arXiv2024

Anyonization of bosons

Anyons are low-dimensional quasiparticles that obey fractional statistics, hence interpolating between bosons and fermions. In two dimensions, they exist as elementary excitations of fractional quantum Hall states and they are believed to enable topological quantum computing. One-dimensional (1D) anyons have been theoretically proposed, but their experimental realization has proven to be difficult. Here, we observe anyonic correlations, which emerge through the phenomenon of spin-charge separation, in a 1D strongly-interacting quantum gas. The required spin degree of freedom is provided by a mobile impurity, whose effective anyonic correlations are associated with an experimentally tunable statistical angle. These anyonic correlations are measured by monitoring the impurity momentum distribution, whose asymmetric feature demonstrates the transmutation of bosons via anyons to fermions. Going beyond equilibrium conditions, we study the dynamical properties of the anyonic correlations via dynamical fermionization of the anyons. Our work opens up the door to the exploration of non-equilibrium anyonic phenomena in a highly controllable setting.

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arXiv2024

Bose-Einstein condensation of non-ground-state caesium atoms

Bose-Einstein condensates of ultracold atoms serve as low-entropy sources for a multitude of quantum-science applications, ranging from quantum simulation and quantum many-body physics to proof-of-principle experiments in quantum metrology and quantum computing. For stability reasons, in the majority of cases the energetically lowest-lying atomic spin state is used. Here we report the Bose-Einstein condensation of caesium atoms in the Zeeman-excited mf = 2 state, realizing a non-ground-state Bose-Einstein condensate with tunable interactions and tunable loss. We identify two regions of magnetic field in which the two-body relaxation rate is low enough that condensation is possible. We characterize the phase transition and quantify the loss processes, finding unusually high three-body losses in one of the two regions. Our results open up new possibilities for the mixing of quantum-degenerate gases, for polaron and impurity physics, and in particular for the study of impurity transport in strongly correlated one-dimensional quantum wires.

cond-mat.quant-gas↗

arXiv2023

Observation of many-body dynamical localization

The quantum kicked rotor is a paradigmatic model system in quantum physics. As a driven quantum system, it is used to study the transition from the classical to the quantum world and to elucidate the emergence of chaos and diffusion. In contrast to its classical counterpart, it features dynamical localization, specifically Anderson localization in momentum space. The interacting many-body kicked rotor is believed to break localization, as recent experiments suggest. Here, we present evidence for many-body dynamical localization for the Lieb-Liniger version of the many-body quantum kicked rotor. After some initial evolution, the momentum distribution of interacting quantum-degenerate bosonic atoms in one-dimensional geometry, kicked hundreds of times by means of a pulsed sinusoidal potential, stops spreading. We quantify the arrested evolution by analysing the energy and the information entropy of the system as the interaction strength is tuned. In the limiting cases of vanishing and strong interactions, the first-order correlation function exhibits a very different decay behavior. Our results shed light on the boundary between the classical, chaotic world and the realm of quantum physics.

quant-ph↗

arXiv2023

Cooling bosons by dimensional reduction

Cold atomic gases provide a remarkable testbed to study the physics of interacting many-body quantum systems. They have started to play a major role as quantum simulators, given the high degree of control that is possible. A crucial element is given by the necessarily non-zero temperature. However cooling to the required ultralow temperatures or even simply measuring the temperature directly on the system can prove to be very challenging tasks. Here, we implement thermometry on strongly interacting two- and one-dimensional Bose gases with high sensitivity in the nano-Kelvin temperature range. Our method is aided by the fact that the decay of the first-order correlation function is very sensitive to the temperature when interactions are strong. We find that there may be a significant temperature variation when the three-dimensional quantum gas is cut into two-dimensional slices or into one-dimensional tubes. Strikingly, the temperature for the one-dimensional case can be much lower than the initial temperature. Our findings show that this decrease results from the interplay of dimensional reduction and strong interactions.

cond-mat.quant-gas↗

arXiv2023

Experimental Observation of the 2D-1D Dimensional Crossover in Strongly Interacting Ultracold Bosons

Dimensionality plays an essential role in determining the nature and properties of a physical system. For quantum systems the impact of interactions and fluctuations is enhanced in lower dimensions, leading to a great diversity of genuine quantum effects for reduced dimensionality. In most cases, the dimension is fixed to some integer value. Here, we experimentally probe the dimensional crossover from two to one dimension using strongly interacting ultracold bosons in variable lattice potentials and compare the data to ab-initio theory that takes into account non-homogeneous trapping and non-zero temperature. From a precise measurement of the momentum distribution we analyze the characteristic decay of the one-body correlation function in the two dimensionalities and then track how the decay is modified in the crossover. A varying two-slope structure is revealed, reflecting the fact that the particles see their dimensionality as being one or two depending on whether they are probed on short or long distances, respectively. Our observations demonstrate how quantum properties in the strongly-correlated regime evolve in the dimensional crossover as a result of the interplay between dimensionality, interactions, and temperature.

cond-mat.quant-gas↗

arXiv2022

Expansion of a quantum gas in a shell trap

We report the observation of the controlled expansion of a two-dimensional quantum gas confined onto a curved shell-shaped surface. We start from the ellipsoidal geometry of a dressed quadrupole trap and introduce a novel gravity compensation mechanism enabling to explore the full ellipsoid. The zero-point energy of the transverse confinement manifests itself by the spontaneous emergence of an annular shape in the atomic distribution. The experimental results are compared with the solution of the three-dimensional Gross-Pitaevskii equation and with a two-dimensional semi-analytical model. This work evidences how a hidden dimension can affect dramatically the embedded low-dimensional system by inducing a change of topology.

cond-mat.quant-gas↗

arXiv2021

A versatile ring trap for quantum gases

We report on the confinement of a Bose-Einstein condensate in an annular trap with widely tunable parameters. The trap relies on a combination of magnetic, optical and radio-frequency fields. The loading procedure is discussed. We present annular traps with radii adjusted between 20 and 150 micrometers. We demonstrate the preparation of persistent flows both with a rotating laser stirrer and with a global quadrupole deformation of the ring.Our setup is well adapted for the study of superfluid dynamics.

cond-mat.quant-gas↗

arXiv2020

Supersonic rotation of a superfluid: a long-lived dynamical ring

We present the experimental realization of a long-lived superfluid flow of a quantum gas rotating in an anharmonic potential, sustained by its own angular momentum. The gas is set into motion by rotating an elliptical deformation of the trap. An evaporation selective in angular momentum yields an acceleration of rotation until the density vanishes at the trap center, resulting in a dynamical ring with 350 hbar angular momentum per particle. The density profile of the ring corresponds to the one of a quasi two-dimensional superfluid, with a linear velocity reaching Mach 18 and a rotation lasting more than a minute.

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