arXiv subjects

Feng Mei

Publications and source records attributed to Feng Mei.

At least 19 recordsLinked to original sources

arXiv2026

Pulse-Controlled Topologically Protected Quantum Batteries

Quantum batteries have emerged as a promising new generation of energy-storage devices for powering quantum technologies. Long-distance charging is particularly attractive because it minimizes interference between the charger and the battery, thereby attracting considerable interest. Here, we propose a topologically protected long-distance charging protocol for quantum batteries based on a pulse-controlled superconducting qubit chain. By dynamically modulating the pulse-mediated couplings, we realize topologically protected energy transfer from the charger to the battery. We show that the charging process is free of energy backflow and remains robust against imperfections in pulse control. Moreover, the energy stored in the battery at the target time is fully extractable, and the protocol remains effective for relatively large system sizes. To further accelerate charging, we optimize the pulse shape and elucidate the underlying physical mechanism. Our pulse-controlled topological quantum battery protocol provides a versatile framework for implementing long-distance topological charging and establishes a theoretical foundation for designing optimal-control strategies to enhance quantum battery performance.

quant-ph↗

arXiv2026

Anomalous Localization and Mobility Edges in Non-Hermitian Quasicrystals with Disordered Imaginary Gauge Fields

Localization in non-Hermitian quasicrystals can differ fundamentally from its Hermitian counterpart when non-reciprocity is spatially disordered. Here we study a one-dimensional non-Hermitian Aubry-Andr\'{e}-Harper chain with a Bernoulli imaginary gauge field and quasiperiodic onsite modulation. In the nearest-neighbor limit, we identify an anomalous transition from a fully erratic non-Hermitian skin effect (ENHSE) phase to a fully localized phase. Although the fractal dimension vanishes in both regimes, the Lyapunov exponent and the fluctuation of the eigenstate center of mass sharply distinguish them. For generic finite-size realizations, this transition is further accompanied by a complex-to-real spectral change under periodic boundary conditions and a change of spectral winding from nontrivial to trivial. With weak next-nearest-neighbor hopping, we uncover an anomalous mobility edge at the same location as in the Hermitian generalized Aubry-Andr\'{e}-Harper model, but separating Anderson-localized states from ENHSE-type macroscopic-accumulation states rather than extended states. We further show that this anomalous localization structure is reflected in spectral winding and wave-packet dynamics: single realizations exhibit winding-dependent drift, winding-resolved averaging preserves opposite directional responses, and full disorder averaging largely restores Hermitian-like transport. Our results establish practical diagnostics of anomalous localization and mobility edges in non-Hermitian quasicrystals.

cond-mat.dis-nn↗

arXiv2025

Entanglement Phase Transition in Chaotic non-Hermitian Systems

We study an entanglement phase transition in a class of chaotic non-Hermitian spin chains whose spin-spin coupling terms commute with the non-Hermitian contributions. Two representative models are investigated: the transverse-field Ising model with a complex longitudinal field and the non-Hermitian XX model with a transverse field. By analyzing their complex spectra, we find that both models undergo a dissipation-induced gapless-gapped phase transition when the transverse field exceeds a model-dependent threshold. Interestingly, the complex gap does not vary monotonically with the dissipation rate; instead, it exhibits pronounced oscillations before entering the gapped phase. By simulating their non-unitary dynamics, we show that the steady-state entanglement entropy undergoes a transition from volume-law to area-law scaling as the dissipation rate increases. Moreover, several unexpected features emerge within the volume-law regime: a larger complex gap or dissipation rate may lead to a more entangled steady state. We trace these unusual behaviors of the complex gap and the steady-state entanglement to level crossings between the maximal imaginary level and other spectral levels. Our work uncovers an exotic entanglement transition in chaotic non-Hermitian many-body systems.

quant-ph↗

arXiv2025

Observation of topological switch between Weyl semimetal and third-order topological insulator phases

Weyl semimetals and higher-order topological insulators represent two fundamental yet distinct classes of topological matter. While both have been extensively studied in classical-wave systems, their coexistence and controllable transition within a single platform remain largely unexplored. Meanwhile, implementing three-dimensional spin-orbit couplings, which is crucial for realizing a broad class of higher-dimensional topological phases, continues to pose significant experimental challenges. Here, we experimentally realize three-dimensional spin-orbit couplings and demonstrate that tuning the dimerized spin-orbit coupling strength enables both the coexistence of and a controllable switch between Weyl semimetal and third-order topological insulator phases. By engineering a three-dimensional circuit metamaterial, we synthesize the required spin-orbit interactions and observe hallmark signatures of both phases: frequency spectroscopy reveals the Fermi arcs, while local density of states measurements identify the topological corner modes. Interestingly, the corner mode degeneracy doubles compared to that in the canonical Benalcazar-Bernevig-Hughes model, signaling an enriched topological structure. Our study establishes a fundamental connection between two paradigmatic topological phases and paves the way for further exploring spin-orbit-coupling induced exotic higher-dimensional topological phases.

cond-mat.mes-hall↗

arXiv2025

Observation of gauge field induced non-Hermitian helical skin effects

Synthetic gauge fields and non-Hermitian skin effects are pivotal to topological phases and non-Hermitian physics, each recently attracting great interest across diverse research fields. Realizing skin effects typically require nonreciprocal couplings or on-site gain and loss. Here, we theoretically and experimentally report that, under gauge fields, reciprocal dissipative couplings can nontrivially give rise to an unprecedented nonreciprocal skin effect, hosting pseudospin degree of freedom and featuring helical transport, dubbed as the ``helical pseudospin skin effect". Before introducing the gauge fields, this model exhibits localized pseudospin edge modes and extended bulk modes, without skin effects. As the gauge field strength is applied from $0$ to $\pi$, we observe the emergence of two distinct pseudospin skin effects and their topological transitions: the hybrid-order and second-order helical pseudospin skin effects. Our findings not only highlight gauge field enriched non-Hermitian topology, but also brings pseudospin-momentum locking into skin effects.

cond-mat.mes-hall↗

arXiv2025

Maximal coin-position entanglement and non-Hermitian skin effect in discrete-time quantum walks

A distinctive feature of non-Hermitian systems is the skin effect, which has attracted widespread attention in recent studies. Quantum walks provide a powerful platform for exploring the underlying mechanisms of the non-Hermitian skin effect. Additionally, the generation of hybrid entanglement in quantum walks is recognized as another crucial property. However, the experimentally exploring the influence of skin effect on the evolution of entanglement dynamical in the non-Hermitian system remains a challenge. In this paper, we present a flexible photonic implementation of discrete-time quantum walks over 20 evolution steps using an optimized time-multiplexed loop configuration. Through optimizing the coin parameter, we achieve maximal coin-position entanglement in 20-steps quantum walks. Moreover, we experimentally measure the polarization-averaged growth rates and the evolution of coin-position entanglement for specific coin and loss parameters. We observe the asymmetric Lyapunov exponent profiles and the suppression of entanglement induced by the skin effect in non-Hermitian systems. Interestingly, this entanglement suppression weakens with increasing coin parameters and enhances with increasing loss parameters and evolution steps. Our results demonstrate the potential of quantum walks as a powerful platform for investigating hybrid entanglement properties and skin effect in non-Hermitian systems.

quant-ph↗

arXiv2025

A Hybrid Cross-Stage Coordination Pre-ranking Model for Online Recommendation Systems

Large-scale recommendation systems often adopt cascading architecture consisting of retrieval, pre-ranking, ranking, and re-ranking stages. With strict latency requirements, pre-ranking utilizes lightweight models to perform a preliminary selection from massive retrieved candidates. However, recent works focus solely on improving consistency with ranking, relying exclusively on downstream stages. Since downstream input is derived from the pre-ranking output, they will exacerbate the sample selection bias (SSB) issue and Matthew effect, leading to sub-optimal results. To address the limitation, we propose a novel Hybrid Cross-Stage Coordination Pre-ranking model (HCCP) to integrate information from upstream (retrieval) and downstream (ranking, re-ranking) stages. Specifically, cross-stage coordination refers to the pre-ranking's adaptability to the entire stream and the role of serving as a more effective bridge between upstream and downstream. HCCP consists of Hybrid Sample Construction and Hybrid Objective Optimization. Hybrid sample construction captures multi-level unexposed data from the entire stream and rearranges them to become the optimal guiding "ground truth" for pre-ranking learning. Hybrid objective optimization contains the joint optimization of consistency and long-tail precision through our proposed Margin InfoNCE loss. It is specifically designed to learn from such hybrid unexposed samples, improving the overall performance and mitigating the SSB issue. The appendix describes a proof of the efficacy of the proposed loss in selecting potential positives. Extensive offline and online experiments indicate that HCCP outperforms SOTA methods by improving cross-stage coordination. It contributes up to 14.9% UCVR and 1.3% UCTR in the JD E-commerce recommendation system. Concerning code privacy, we provide a pseudocode for reference.

cs.IR↗

arXiv2024

Observation of higher-order time-dislocation topological modes

Topological dislocation modes resulting from the interplay between spatial dislocations and momentum-space topology have recently attracted significant interest. Here, we theoretically and experimentally demonstrate time-dislocation topological modes which are induced by the interplay between temporal dislocations and Floquet-band topology. By utilizing an extra physical dimension to represent the frequency-space lattice, we implement a two-dimensional Floquet higher-order topological phase and observe time-dislocation induced $\pi$-mode topological corner modes in a three-dimensional circuit metamaterial. Intriguingly, the realized time-dislocation topological modes exhibit spatial localization at the temporal dislocation, despite homogeneous in-plane lattice couplings across it. Our study opens a new avenue to explore the topological phenomena enabled by the interplay between real-space, time-space and momentum-space topology.

cond-mat.mes-hall↗

arXiv2024

Generalized Aubry-Andre-Harper Models in Optical Superlattices

Ultracold atoms trapped in optical superlattices provide a simple platform for realizing the seminal Aubry-Andr\'{e}-Harper (AAH) model. However, the periodic modulations on the nearest-neighbour hoppings have been ignored in this model. In this paper, we find that optical superlattice system actually can be approximately described by a generalized AAH model in the case of $V_1\gg V_2$, with periodic modulations on both on-site energies and nearest-neighbour hoppings, supporting much richer topological properties that are absent in the standard AAH model. Specifically, by calculating Chern numbers and topological edge states, we show that the generalized AAH model possesses multifarious topological phases and topological phase transitions, as compared to the standard AAH model only supporting a single topological phase. Our findings can open up more opportunities for using optical superlattices to study topological and localization physics.

cond-mat.quant-gas↗

arXiv2024

Topological optical Raman superlattices

Topological phases of ultracold atoms recently have been intensively studied both in optical superlattices and Raman lattices. However, the topological features induced by the interplay between such two lattices remain largely unexplored. Here, we present an optical Raman superlattice system that incorporates an optical superlattice and a Raman superlattice. The Raman superlattice presented here supports tunable dimerized spin-orbit couplings and staggered on-site spin flips. We find that such system respects a spin-rotation symmetry and has much richer topological properties. Specifically, we show that various topological phases could emerge in the optical Raman superlattice, such as four different chiral topological insulator phases and two different quantum spin Hall insulator phases, identified by spin winding and spin Chern numbers respectively. We also demonstrate that the spin-dependent topological invariants could be directly measured by quench dynamics.

cond-mat.quant-gas↗

arXiv2024

Dynamical Detection of Topological Spectral Density

Local density of states (LDOS) is emerging as powerful means of exploring synthetic topological phases. However, the current LDOS detection method remains rare and merely works for static situations. Here, we introduce a generic dynamical method to detect both the static and Floquet LDOS, based on an elegant connection between dynamics of chiral density and local spectral densities. Moreover, we find that the Floquet LDOS allows to measure out Floquet quasienergy spectra and identify topological $\pi$ modes. As an example, we demonstrate that both the static and Floquet higher-order topological phase can be universally identified via LDOS detection, regardless of whether the topological corner modes are in energy gaps, bands or continue energy spectra without bandgaps. Our study opens a new avenue utilizing dynamics to detect topological spectral densities and provides a universal approach of identifying static and Floquet topological phases.

cond-mat.mes-hall↗

arXiv2024

PPM : A Pre-trained Plug-in Model for Click-through Rate Prediction

Click-through rate (CTR) prediction is a core task in recommender systems. Existing methods (IDRec for short) rely on unique identities to represent distinct users and items that have prevailed for decades. On one hand, IDRec often faces significant performance degradation on cold-start problem; on the other hand, IDRec cannot use longer training data due to constraints imposed by iteration efficiency. Most prior studies alleviate the above problems by introducing pre-trained knowledge(e.g. pre-trained user model or multi-modal embeddings). However, the explosive growth of online latency can be attributed to the huge parameters in the pre-trained model. Therefore, most of them cannot employ the unified model of end-to-end training with IDRec in industrial recommender systems, thus limiting the potential of the pre-trained model. To this end, we propose a $\textbf{P}$re-trained $\textbf{P}$lug-in CTR $\textbf{M}$odel, namely PPM. PPM employs multi-modal features as input and utilizes large-scale data for pre-training. Then, PPM is plugged in IDRec model to enhance unified model's performance and iteration efficiency. Upon incorporating IDRec model, certain intermediate results within the network are cached, with only a subset of the parameters participating in training and serving. Hence, our approach can successfully deploy an end-to-end model without causing huge latency increases. Comprehensive offline experiments and online A/B testing at JD E-commerce demonstrate the efficiency and effectiveness of PPM.

cs.IR↗

arXiv2023

A spectrum-based shortcut method for topological systems

The need for fast and robust quantum state transfer is an essential element in scalable quantum information processing, leading to widespread interest in shortcuts to adiabaticity for speeding up adiabatic quantum protocols. However, shortcuts to adiabaticity for systems with more than a few levels is occasionally challenging to compute in theory and frequently difficult to implement in experiments. In this work, we develop a protocol for constructing shortcuts to adiabaticity through the multi-state Landau-Zener approach and a stricter adiabatic condition. Importantly, our protocol only requires a few pieces of information about the energy spectrum and just adjusts the evolutionary rate of the system. It means that our protocol has broad applicability to theoretical models and does not require increasing the difficulty of the experiment. As examples, we apply our protocol to state transfer in the two-level Landau-Zener model, the non-Hermitian Su-Schrieffer-Heeger (SSH) model and the topological Thouless pump model and find that it can speed up the manipulation speed while remaining robust to Hamiltonian errors. Furthermore, based on the experimental friendliness of our findings, it can potentially be extended to many-body systems, dissipation cases, or Floquet processes. Overall, the proposed shortcut protocol offers a promising avenue for enhancing the efficiency and reliability of quantum state transfer protocols.

quant-ph↗

arXiv2023

Entanglement Dynamics of two Non-Hermitian Qubits

The evolution of entanglement in a non-Hermitian quantum system may behave differently compared to its Hermitian counterpart. In this paper, we investigate the entanglement dynamics of two coupled and driven non-Hermitian qubits. Through calculating the concurrence of the system, we find that the evolution of the bipartite entanglement manifests two distinct patterns in the parameter space. In the low non-Hermiticity regime, the concurrence oscillates significantly, while in the opposite regime the same quantity would trend to a stable value. We attribute this phenomenon to parity-time ($ \mathcal{PT}$) symmetry phase transition. In addition, we have also studied the effect of decoherence on the entanglement dynamics. Our research provides a method to stabilize entanglement by exploiting non-Hermiticity.

quant-ph↗

arXiv2023

Observation of Large-Number Corner Modes in $\mathbb{Z}$-class Higher-Order Topolectrical Circuits

Topological corner states are exotic topological boundary states that are bounded to zero-dimensional geometry even the dimension of systems is large than one. As an elegant physical correspondence, their numbers are dictated by the bulk topological invariants. So far, all previous realizations of HOTIs are hallmarked by $\mathbb{Z}_2$ topological invariants and therefore have only one corner state at each corner. Here we report an experimental demonstration of $\mathbb{Z}$-class HOTI phases in electric circuits, hosting $N$ corner modes at each single corner structure. By measuring the impedance spectra and distributions, we clearly demonstrate the $\mathbb{Z}$-class HOTI phases, including the zero-energy corner modes and their density distributions. Moreover, we reveal that the local density of states (LDOS) at each corner for $N=4$ are equally distributed at four corner unit cells, prominently differing from $\mathbb{Z}_2$-class case where the LDOS only dominates over one corner unit cell. Our results extend the observation of HOTIs from $\mathbb{Z}_2$ class to $\mathbb{Z}$ class and the coexistence of spatially overlapped large number of corner modes which may enable exotic topological devices that require high degeneracy boundary states.

cond-mat.mes-hall↗

arXiv2022

Observation of interaction-induced mobility edge in a disordered atomic wire

Mobility edge, a critical energy separating localized and extended excitations, is a key concept for understanding quantum localization. Aubry-Andr\'{e} (AA) model, a paradigm for exploring quantum localization, does not naturally allow mobility edges due to self-duality. Using the momentum-state lattice of quantum gas of Cs atoms to synthesize a nonlinear AA model, we provide experimental evidence for mobility edge induced by interactions. By identifying the extended-to-localized transition of different energy eigenstates, we construct a mobility-edge phase diagram. The location of mobility edge in the low- or high-energy region is tunable via repulsive or attractive interactions. Our observation is in good agreement with the theory, and supports an interpretation of such interaction-induced mobility edge via a generalized AA model. Our work also offers new possibilities to engineer quantum transport and phase transitions in disordered systems.

quant-ph↗

arXiv2021

Topological nodal chains in optical lattices

Topological nodal rings as the simplest topological nodal lines recently have been extensively studied in optical lattices. However, the realization of complex nodal line structures like nodal chains in this system remains a crucial challenge. Here we propose an experimental scheme to realize and detect topological nodal chains in optical Raman lattices. Specifically, we construct a three-dimensional optical Raman lattice which supports next nearest-neighbor spin-orbit couplings and hosts topological nodal chains in its energy spectra. Interestingly, the realized nodal chains are protected by mirror symmetry and could be tuned into a large variety of shapes, including the inner and outer nodal chains. We also demonstrate that the shapes of the nodal chains could be detected by measuring spin polarizations. Our study opens up the possibility of exploring topological nodal-chain semimetal phases in optical lattices.

cond-mat.quant-gas↗

arXiv2020

Digital Quantum Simulation of Floquet Topological Phases with a Solid-State Quantum Simulator

Quantum simulator with the ability to harness the dynamics of complex quantum systems has emerged as a promising platform for probing exotic topological phases. Since the flexibility offered by various controllable quantum systems has enabled to gain insight into quantum simulation of such complicated problems, analog quantum simulator has recently shown its feasibility to tackle problems of exploring topological phases. However, digital quantum simulation and detection of topological phases still remain elusive. Here, we develop and experimentally realize the digital quantum simulation of topological phase with a solid-state quantum simulator at room temperature. Distinct from previous works dealing with static topological phases, the topological phases emulated here are Floquet topological phases. Furthermore, we also illustrate the procedure of digitally simulating a quantum quench and observing the nonequilibrium dynamics of Floquet topological phases. By means of quantum quench, the 0- and {\pi}-energy topological invariants are unambiguously detected through measuring time-averaged spin polarizations. Our experiment opens up a new avenue to digitally simulate and detect Floquet topological phases with fast-developed programmable quantum simulators.

quant-ph↗