arXiv subjects

Wei Yi

Publications and source records attributed to Wei Yi.

At least 55 records · Page 3Linked to original sources

arXiv2024

Nonlinear dynamics and stability analysis of locally-active Mott memristors using a physics-based compact model

Locally-active memristors are a class of emerging nonlinear dynamic circuit elements that hold promise for scalable yet biomimetic neuromorphic circuits. Starting from a physics-based compact model, we performed small-signal linearization analyses and applied Chua's local activity theory to a one-dimensional locally-active vanadium dioxide Mott memristor based on an insulator-to-metal phase transition. This approach allows a connection between the dynamical behaviors of a Mott memristor and its physical device parameters as well as a complete mapping of the locally passive and edge of chaos domains in the frequency and current operating parameter space, which could guide materials and device development for neuromorphic circuit applications. We also examined the applicability of local analyses on a second-order relaxation oscillator circuit that consists of a voltage-biased vanadium dioxide memristor coupled to a parallel reactive capacitor element and a series resistor. We show that global nonlinear techniques, including nullclines and phase portraits, provide insights on instabilities and persistent oscillations near non-hyperbolic fixed points, such as a supercritical Hopf-like bifurcation from an unstable spiral to a stable limit cycle, with each of the three circuit parameters acting as a bifurcation parameter. The abruptive growth in the limit cycle resembles the Canard explosion phenomenon in systems exhibiting relaxation oscillations. Finally, we show that experimental limit cycle oscillations in a vanadium dioxide nano-device relaxation oscillator match well with SPICE simulations built upon the compact model.

cs.ET↗

arXiv2024

Biorthogonal topological charge pumping in non-Hermitian systems

We study charge pumping in generic non-Hermitian settings and show that quantized charge pumping is only guaranteed under a biorthogonal formalism therein, where the charge transport is evaluated using the left and right eigenvectors of the non-Hermitian Hamiltonian. Specifically, for biorthogonal charge pumping in generic one-dimensional non-Hermitian models, we demonstrate how quantized transport is related to the Chern number in the parameter space. When the non-Hermitian model possesses the non-Hermitian skin effect, under which Bloch states in the bulk are deformed and localize toward boundaries, we propose a scenario where the pumped charge is related to the non-Bloch Chern number defined in the parameter space involving the generalized Brillouin zone. We illustrate the validity of our analytic results using concrete examples and, in the context of the biorthogonal charge pumping, discuss in detail a recent experiment where quantized charge pumping was observed in a lossy environment.

cond-mat.mes-hall↗

arXiv2024

Interaction-Enhanced Superradiance of a Ryderg-Atom Array

We study the superradiant phase transition of an array of Rydberg atoms in a dissipative microwave cavity. Under the interplay of the cavity field and the long-range Rydberg interaction, the steady state of the system exhibits an interaction-enhanced superradiance, with vanishing critical atom-cavity coupling rates at a discrete set of interaction strengths. We find that, while the phenomenon can be analytically understood in the case of a constant all-to-all interaction, the enhanced superradiance persists under typical experimental parameters with spatially dependent interactions, but at modified critical interaction strengths. The diverging susceptibility at these critical points is captured by emergent quantum Rabi models, each of which comprises a pair of collective atomic states with different numbers of atomic excitations. These collective states become degenerate at the critical interaction strengths, resulting in a superradiant phase for an arbitrarily small atom-cavity coupling.

quant-ph↗

arXiv2024

Chiral switching of many-body steady states in a dissipative Rydberg gas

Dissipative Rydberg gases are an outstanding platform for the investigation of many-body quantum open systems. Despite the wealth of existing studies, the non-equilibrium dynamics of dissipative Rydberg gases are rarely examined or harnessed from the perspective of non-Hermitian physics, which is but intrinsic to open systems. Here we report the experimental observation of a chiral switching between many-body steady states in a dissipative thermal Rydberg vapor, where the interplay of many-body effects and non-Hermiticity plays a key role. Specifically, as the parameters are adiabatically varied around a closed contour, depending on the chirality of the parameter modulation, the Rydberg vapor can change between two collective steady states with distinct Rydberg excitations and optical transmissions. Adopting a mean-field description, we reveal that both the existence of the bistable steady states and chiral dynamics derive from an exceptional structure in the parameter space, where multiple steady states of the many-body Liouvillian superoperator coalesce. We demonstrate that both the exceptional structure and the resulting state-switching dynamics are tunable through microwave dressing and temperature variations, confirming their reliance on the many-body dissipative nature of the Rydberg vapor.

cond-mat.quant-gas↗

arXiv2024

Subspace-Based Detection in OFDM ISAC Systems under Different Constellations

This paper investigates subspace-based target detection in OFDM integrated sensing and communications (ISAC) systems, considering the impact of various constellations. To meet diverse communication demands, different constellation schemes with varying modulation orders (e.g., PSK, QAM) can be employed, which in turn leads to variations in peak sidelobe levels (PSLs) within the radar functionality. These PSL fluctuations pose a significant challenge in the context of multi-target detection, particularly in scenarios where strong sidelobe masking effects manifest. To tackle this challenge, we have devised a subspace-based approach for a step-by-step target detection process, systematically eliminating interference stemming from detected targets. Simulation results corroborate the effectiveness of the proposed method in achieving consistently high target detection performance under a wide range of constellation options in OFDM ISAC systems.

eess.SP↗

arXiv2024

Chiral Dynamics of Ultracold Atoms under a Tunable SU(2) Synthetic Gauge Field

Surface currents emerge in superconductors exposed to magnetic fields, and are a key signature of the Meissner effect. Analogously, chiral dynamics were observed in quantum simulators under synthetic Abelian gauge fields. The flexible control of these simulators also facilitates the engineering of non-Abelian gauge fields, but their impact on the chiral dynamics remains elusive. Here, by employing the cutting-edge momentum-lattice technique, we implement a synthetic SU(2) gauge field in a spinful 1D ladder and study the rich chiral dynamics therein. We confirm the non-Abelian nature of the synthetic potential by observing the non-Abelian Aharonov-Bohm effect on a single plaquette. More importantly, the chiral current along the two legs of the ladder is observed to be spin-dependent and highly tunable through the parameters of the gauge potential. We experimentally map out different dynamic regimes of the chiral current, and reveal the underlying competition between overlaying flux ladders with distinct spin compositions. Our experiment demonstrates the dramatic impact of non-Abelian gauge fields on the system dynamics, paving the way for future studies of exotic synthetic gauge fields on the versatile platform of momentum lattices.

cond-mat.quant-gas↗

arXiv2024

Engineering topological chiral transport in a flat-band lattice of ultracold atoms

The manipulation of particle transport in synthetic quantum matter is an active research frontier for its theoretical importance and potential applications. Here we experimentally demonstrate an engineered topological transport in a synthetic flat-band lattice of ultracold $^{87}$Rb atoms. We implement a quasi-one-dimensional rhombic chain with staggered flux in the momentum space of the atomic condensate and observe biased local oscillations that originate from the interplay of the staggered flux and flat-band localization under the mechanism of Aharonov-Bohm caging. Based on these features, we design and experimentally confirm a state-dependent chiral transport under the periodic modulation of the synthetic flux. We show that the phenomenon is topologically protected by the winding of the Floquet Bloch bands of a coarse-grained effective Hamiltonian. The observed chiral transport offers a strategy for efficient quantum device design where topological robustness is ensured by fast Floquet driving and flat-band localization.

cond-mat.quant-gas↗

arXiv2023

Exceptional entanglement phenomena: non-Hermiticity meeting non-classicality

Non-Hermitian (NH) extension of quantum-mechanical Hamiltonians represents one of the most significant advancements in physics. During the past two decades, numerous captivating NH phenomena have been revealed and demonstrated, but all of which can appear in both quantum and classical systems. This leads to the fundamental question: what NH signature presents a radical departure from classical physics? The solution of this problem is indispensable for exploring genuine NH quantum mechanics, but remains experimentally untouched so far. Here, we resolve this basic issue by unveiling distinct exceptional entanglement phenomena, exemplified by an entanglement transition, occurring at the exceptional point of NH interacting quantum systems. We illustrate and demonstrate such purely quantum-mechanical NH effects with a naturally dissipative light-matter system, engineered in a circuit quantum electrodynamics architecture. Our results lay the foundation for studies of genuinely quantum-mechanical NH physics, signified by exceptional-point-enabled entanglement behaviors.

quant-ph↗

arXiv2023

Self acceleration from spectral geometry in dissipative quantum-walk dynamics

Dynamic behaviors of a physical system often originate from its spectral properties. In open systems, where the effective non-Hermitian description enables a wealth of spectral structures on the complex plane, the concomitant dynamics is significantly enriched, whereas the identification and comprehension of the underlying connections are challenging. Here we experimentally demonstrate the correspondence between the transient self acceleration of local excitations and the non-Hermitian spectral topology using lossy photonic quantum walks. Focusing first on one-dimensional quantum walks, we show that the measured short-time acceleration of the wave function is proportional to the area enclosed by the eigenspectrum. We then reveal similar correspondence in two-dimension quantum walks, where the self acceleration is proportional to the volume enclosed by the eigenspectrum in the complex parameter space. In both dimensions, the transient self acceleration crosses over to a long-time behavior dominated by a constant flow at the drift velocity. Our results unveil the universal correspondence between spectral topology and transient dynamics, and offer a sensitive probe for phenomena in non-Hermitian systems that originate from spectral geometry.

cond-mat.mes-hall↗

arXiv2023

Tuning excitation transport in a dissipative Rydberg ring

We demonstrate the flexible tunability of excitation transport in Rydberg atoms, under the interplay of controlled dissipation and interaction-induced synthetic flux. Considering a minimum four-site setup -- a triangular configuration with an additional output site -- we study the transport of a single excitation, injected into a vertex of the triangle, through the structure. While the long-range dipole-dipole interactions between the Rydberg atoms lead to geometry-dependent Peierls phases in the hopping amplitudes of excitations, we further introduce on-site dissipation to a vertex of the triangle. As a result, both the chirality and destination of the transport can be manipulated through the flux and dissipation. In particular, we illustrate a parameter regime where our Rydberg-ring structure may serve as a switch for transporting the injected excitation through to the output site. The underlying mechanism is then analyzed by studying the chiral trajectory of the excitation and the time-dependent dissipation.

physics.atom-ph↗

arXiv2023

Many-body non-Hermitian skin effect under dynamic gauge coupling

We study an atom-cavity hybrid system where fermionic atoms in a one-dimensional lattice are subject to a cavity-induced dynamic gauge potential. The gauge coupling leads to highly-degenerate steady states in which the fermions accumulate to one edge of the lattice under an open boundary condition. Such a phenomenon originates from the many-body Liouvillian superoperator of the system, which, being intrinsically non-Hermitian, is unstable against boundary perturbations and manifests the non-Hermitian skin effect. Contrary to the single-body case, the steady state of a multi-atom system is approached much slower under the open boundary condition, as the long-time damping of the cavity mode exhibits distinct rates at different times. This stage-wise slowdown is attributed to the competition between light-assisted hopping and the dynamic gauge coupling, which significantly reduces the steady-state degeneracy under the open boundary condition, as distinct hosts of quasi-steady states dominate the dynamics at different time scales.

cond-mat.quant-gas↗

arXiv2023

Experimental Simulation of Symmetry-Protected Higher-Order Exceptional Points with Single Photons

Exceptional points (EPs) of non-Hermitian (NH) systems have recently attracted increasing attention due to their rich phenomenology and intriguing applications. Compared to the predominantly studied second-order EPs, higher-order EPs have been assumed to play a much less prominent role because they generically require the tuning of more parameters. Here we experimentally simulate two-dimensional topological NH band structures using single-photon interferometry, and observe topologically stable third-order EPs obtained by tuning only two real parameters in the presence of symmetry. In particular, we explore how different symmetries stabilize qualitatively different third-order EPs: the parity-time symmetry leads to a generic cube-root dispersion, while a generalized chiral symmetry implies a square-root dispersion coexisting with a flat band. Additionally, we simulate fourfold degeneracies, composed of the non-defective twofold degeneracies and second-order EPs. Our work reveals the abundant and conceptually richer higher-order EPs protected by symmetries and offers a versatile platform for further research on topological NH systems.

cond-mat.mes-hall↗

arXiv2023

Team AcieLee: Technical Report for EPIC-SOUNDS Audio-Based Interaction Recognition Challenge 2023

In this report, we describe the technical details of our submission to the EPIC-SOUNDS Audio-Based Interaction Recognition Challenge 2023, by Team "AcieLee" (username: Yuqi\_Li). The task is to classify the audio caused by interactions between objects, or from events of the camera wearer. We conducted exhaustive experiments and found learning rate step decay, backbone frozen, label smoothing and focal loss contribute most to the performance improvement. After training, we combined multiple models from different stages and integrated them into a single model by assigning fusion weights. This proposed method allowed us to achieve 3rd place in the CVPR 2023 workshop of EPIC-SOUNDS Audio-Based Interaction Recognition Challenge.

cs.SD↗

arXiv2023

Quantum Criticality of Liquid-Gas Transition in a Binary Bose Mixture

Quantum liquid, in the form of a self-bound droplet, is stabilized by a subtle balance between the mean-field contribution and quantum fluctuations. While a liquid-gas transition is expected when such a balance is broken, it remains elusive whether liquid-gas critical points exist in the quantum regime. Here we study the quantum criticality in a binary Bose mixture undergoing the liquid-gas transition. We show that, beyond a narrow stability window of the self-bound liquid, a liquid-gas coexistence persists, which eventually transits into a homogeneous mixture. Importantly, we identify two distinct critical points where the liquid-gas coexistence terminates. These critical points are characterized by rich critical behaviors in their vicinity, including divergent susceptibility, unique phonon-mode softening, and enhanced density correlations. The liquid-gas transition and the critical points can be readily explored in ultracold atoms confined to a box potential. Our work highlights the thermodynamic approach as a powerful tool in revealing the quantum liquid-gas criticality, and paves the way for further studies of critical phenomena in quantum liquids.

cond-mat.quant-gas↗

arXiv2023

Observation of non-Hermitian edge burst in quantum dynamics

The non-Hermitian skin effect, by which the eigenstates of Hamiltonian are predominantly localized at the boundary, has revealed a strong sensitivity of non-Hermitian systems to the boundary condition. Here we experimentally observe a striking boundary-induced dynamical phenomenon known as the non-Hermitian edge burst, which is characterized by a sharp boundary accumulation of loss in non-Hermitian time evolutions. In contrast to the eigenstate localization, the edge burst represents a generic non-Hermitian dynamical phenomenon that occurs in real time. Our experiment, based on photonic quantum walks, not only confirms the prediction of the phenomenon, but also unveils its complete space-time dynamics. Our observation of edge burst paves the way for studying the rich real-time dynamics in non-Hermitian topological systems.

cond-mat.mes-hall↗

arXiv2023

Poisson Conjugate Prior for PHD Filtering based Track-Before-Detect Strategies in Radar Systems

A variety of filters with track-before-detect (TBD) strategies have been developed and applied to low signal-to-noise ratio (SNR) scenarios, including the probability hypothesis density (PHD) filter. Assumptions of the standard point measurement model based on detect-before-track (DBT) strategies are not suitable for the amplitude echo model based on TBD strategies. However, based on different models and unmatched assumptions, the measurement update formulas for DBT-PHD filter are just mechanically applied to existing TBD-PHD filters. In this paper, based on the Kullback-Leibler divergence minimization criterion, finite set statistics theory and rigorous Bayes rule, a principled closed-form solution of TBD-PHD filter is derived. Furthermore, we emphasize that PHD filter is conjugated to the Poisson prior based on TBD strategies. Next, a capping operation is devised to handle the divergence of target number estimation as SNR increases. Moreover, the sequential Monte Carlo implementations of dynamic and amplitude echo models are proposed for the radar system. Finally, Monte Carlo experiments exhibit good performance in Rayleigh noise and low SNR scenarios.

cs.CV↗

arXiv2023

Dissipative two-dimensional Raman lattice

We show that a dissipative two-dimensional Raman lattice can be engineered in a two-component ultracold atomic gas, where the interplay of the two-dimensional spin-orbit coupling and lightinduced atom loss gives rise to a density flow diagonal to the underlying square lattice. The flow is driven by the non-Hermitian corner skin effect, under which eigenstates localize toward one corner of the system. We illustrate that the topological edge states of the system can only be accounted for by the non-Bloch band theory where the deformation of the bulk eigenstates are explicitly considered. The directional flow can be detected through the dynamic evolution of an initially localized condensate in the lattice, or by introducing an immobile impurity species that interact spin-selectively with a condensate in the ground state of the Raman lattice.

cond-mat.quant-gas↗

arXiv2022

Chiral state transfer under dephasing

Exceptional points emerge in the complex eigenspecra of non-Hermitian systems, and give rise to rich critical behaviors. An outstanding example is the chiral state transfer, where states can swap under an adiabatic encircling around the exceptional point, but only along one direction. In dissipative quantum systems, such exceptional-point encirclings are often accompanied by decoherence, whose impact is beyond the description of non-Hermitian Hamiltonians. In this work, we study in detail the effects of dephasing on the encircling dynamics, adopting the full Lindblad master equation. Introducing experimentally relevant quantum-jump processes that account for dephasing, we show that gaps emerge in the eigenspectra landscape of the corresponding Liouvillian superoperator. It follows that the chiral state transfer does not take place in the adiabatic limit, since the system always adiabatically follows the quasi-steady state of the Liouvillian regardless of the encircling direction. Nevertheless, the chirality is restored at intermediate encircling times, where the dynamics is non-adiabatic in both encircling directions, distinct from the typical chiral state transfer in non-Hermitian systems. While our results are applicable to several recent experiments, we examine a recent cold-atom experiment in particular, and show that the observed long-time chirality is but limited to the special encircling path therein. Our study provides further insight into the chiral state transfer under experimental conditions, and is helpful for controlling open-system dynamics from the perspective of non-Hermitian physics.

quant-ph↗