arXiv subjects

Yu-Qiang Ma

Publications and source records attributed to Yu-Qiang Ma.

12 recordsLinked to original sources

arXiv2026

Floquet-sideband-enhanced shortwave electrometry with Rydberg atoms

Rydberg atomic electric-field sensors, under the framework of optical excitation and readout, can overcome the size-to-wavelength constraint imposed by the Chu limit. However, their sensitivity for decametric-wavelength shortwave electric fields is substantially lower than that for microwave ones, stemming from the off-resonant nature of low-frequency signals with Rydberg transitions. Here, we demonstrate a high-sensitivity heterodyne shortwave sensor based on microwave-dressed Rydberg atoms, leveraging precisely modulated Floquet sidebands. Around local- and microwave-field-engineered Floquet sidebands, the steep response gradient, arising from the enhanced atom-shortwave interaction through additionally created coherent channels, induces pronounced amplification of the heterodyne intermediate-frequency signal. As a result, compared to the same atomic heterodyne setup without microwave modulation, such Floquet-sideband-enhanced shortwave measurement boosts the sensitivity by four orders of magnitude, yielding a sensitivity of -122.7 dBm/Hz for shortwave at 30 MHz. This work offers a potential route to high-sensitive portable shortwave receivers in radio astronomy, radar and long-distance communications.

physics.atom-ph↗

arXiv2026

Entanglement-enabled Criticality in One-dimensional Quantum Contact Process

The contact process is a paradigmatic example of nonequilibrium dynamics, with broad applications ranging from chemistry to sociology. Its quantum counterpart, the quantum contact process (QCP), extends the classical model to include coherent processes. Despite sustained interest, the nature of the transition in the one-dimensional (1D) QCP remains debatable. Here, combining Liouvillian spectral analysis, the tensor jump method, exact quantum jump Monte Carlo, and truncated Wigner simulations, we show that 1D QCP undergoes a continuous absorbing-state phase transition, with critical exponents distinct from the classical case. We further find Liouvillian gap closes well below the critical point, highlighting that spectral gap analysis alone cannot distinguish a phase transition from metastability in the QCP. Crucially, the 1D QCP is weakly entangled, yet even this weak entanglement is indispensable for capturing the correct critical behavior, whereas semiclassical methods artificially stabilize the active state and predict a spurious first-order transition. Our work establishes the quantum origin of the phase transition in the 1D QCP and underscores the essential role of entanglement in dissipative quantum many-body systems.

quant-ph↗

arXiv2026

Dynamical Tipping in a Quantum Limit Cycle

Nonequilibrium systems maintain spatiotemporal order through energy dissipation and entropy production. Here, we demonstrate this principle by engineering a quantum limit cycle that emerges from the interplay between a first-order absorbing-state phase transition and feedback mechanism coupling order and control parameters. The quantum limit cycle manifests dynamical correlations driven by multiplicative quantum noise and periodic traverses through tipping points, which act as a robust early-warning signal for state transitions. This periodic crossing results in the enhanced dynamical susceptibility and transient rise of long-range correlations near each tipping event and their subsequent disappearance away from it. These critical transitions are accompanied by a sharp increase in the energy dissipation rate, leading to a stepwise accumulation of dynamical entropy production over time. Our results provide a way for realizing dynamical fluctuations and long-range correlations in strongly interacting driven-dissipative open quantum systems.

quant-ph↗

arXiv2026

Enhanced Microwave Sensing with Dissipative Continuous Time Crystals

A dissipative time crystal is an emergent phase in driven-dissipative quantum many-body systems, characterized by sustained oscillations that break time-translation symmetry spontaneously. Here, we explore nonequilibrium phase transitions in a dissipative Rydberg system driven by a microwave (MW) field and demonstrate their critical sensitivity to high-precision MW sensing. Distinct dynamical regimes are identified, including monostable, bistable, and oscillatory phases under mean-field coupling. Unlike single-particle detection--where the beating signal decays linearly with MW field strength--the time crystalline phase exhibits high sensitivity to MW perturbations, with rapid, discontinuous frequency switching near the monostable-oscillatory boundary. The abrupt transition is rooted in spontaneous symmetry breaking in time and is fundamentally insensitive to the background noise. On this basis, a minimum detectable MW field strength on the order of 1nV/cm is achieved by leveraging this sensitivity. Our results establish a framework for controlling time crystalline phases with external fields and advance MW sensing through many-body effects.

cond-mat.quant-gas↗

arXiv2025

ATP-Independent Entropy-Driven dsRNA Unwinding by DDX3X Revealed by Coarse-Grained Simulations and Deep Learning

DEAD-box RNA helicases (DDXs) are traditionally known as ATP-dependent motors that unwind double-stranded RNA (dsRNA). Recent experiments, however, show that some DDXs promote dsRNA unwinding even in the absence of ATP, raising a fundamental question about the physical mechanism underlying ATP-independent strand separation. Here, we develop a minimal, physics-based coarse-grained RNA model and incorporate weak, specific interactions between DDX3X and dsRNA, revealing the inherently stochastic nature of unwinding events. The unwinding process must overcome an energy barrier, but thermal fluctuations and entropy gain provide a driving force for RNA remodeling. We identify that dsRNA separation proceeds through rare yet obligatory strand-displacing intermediates facilitated by DDX3X. By combining deep learning-assisted analysis, we further rank the contributions of different entropic components, revealing hydrogen bonding as the dominate factor, followed by base stacking and then the backbone conformation. These findings reveal a previously unrecognized physical mechanism for RNA duplex unwinding and offer an effective framework for studying RNA remodeling kinetics.

q-bio.BM↗

arXiv2025

Quantum predator-prey cycles in dissipative Rydberg array

The predator-prey cycle is a paradigmatic example of self-organized population oscillations in far-from-equilibrium systems, yet testing its underlying mechanism in natural ecosystems is often precluded by uncontrollable microscopic parameters. Here, we propose a quantum analogue of predator-prey dynamics using a tunable two-dimensional Rydberg atom array. Through mean-field analysis and large-scale numerical simulations based on the open-system discrete truncated Wigner approximation, we demonstrate stable predator-prey cycles of Rydberg excitations on microsecond timescales. We show that nonperturbative quantum coherence drives spontaneous time-translation symmetry breaking, leading to globally synchronized oscillations under short-range interactions. Even under desynchronization caused by quantum jumps, locally synchronized predator-prey cycles persist, with amplitude scaling inversely with the square root of the system size. Our work extends the study of predator-prey models to the quantum realm and advances quantum simulation strategies that leverage engineered many-body nonequilibrium effects.

quant-ph↗

arXiv2025

Anomalous Criticality of Absorbing State Transition toward Jamming

Jamming transition is traditionally regarded as a geometric transition governed by static contact networks. Recently, dynamic phase transitions of athermal particles under periodic shearing provide a new lens on this problem, leading to a conjecture that jamming transition corresponds to an absorbing-state transition within the Manna (conserved directed percolation) universality class. Here, by re-examining biased random organization models, minimal models for particles under periodic shearing that the conjecture is based on, we uncover several criticality anomalies at high density at odds with the Manna universality class. In three-dimensional monodisperse systems, we find crystallization disrupts the absorbing transition, while in dense binary mixtures, a distinct transition from absorbing to active-glass state emerges, signifying a new dynamic universality class. Close to the jamming point, the quenched heterogeneity in the contact network of binary systems smears the dynamic criticality via Griffiths effects and drives the system toward heterogeneous directed percolation. For close-packed crystal structures, Griffiths effect is absent. However, the dynamic criticality still seems to deviate from the Manna model. These phenomena are explained by a field theory with fractional time dynamics that links jamming, disorder and dynamic criticality.

cond-mat.stat-mech↗

arXiv2025

Liquid-Gas Criticality of Hyperuniform Fluids

In statistical physics, it is well established that the liquid-gas (LG) phase transition with divergent critical fluctuations belongs to the Ising universality class. Whether non-equilibrium effects can alter this universal behavior remains a fundamental open question. In this work, we theoretically prove that non-equilibrium hyperuniform (HU) fluids with additional center-of-mass conservation exhibit LG criticality different from the Ising universality class. As a specific case, we investigate a 2D HU fluid composed of active spinners, where phase separation is driven by dissipative collisions. Strikingly, at the critical point, the 2D HU fluid displays finite density fluctuations $S(q)\sim q^{\eta}$ with $\eta=0$, while the compressibility still diverges. The critical point is thus calm yet highly susceptible, in fundamental violation of the conventional fluctuation-dissipation relation. Consistently, we observe short-range pair correlation functions coexisting with quasi-long-range response functions at the critical point. Based on a generalized Model B and renormalization-group analysis, we prove that hyperuniformity reduces the upper critical dimension $d_c$ from $4$ to $2$. Moreover, the critical point exhibits Gaussian density fluctuations and non-divergent energy fluctuations. Furthermore, the HU fluid undergoes non-conventional spinodal decomposition. The origin of the above anomalies lies in the non-equilibrium nature of the system which obeys a generalized fluctuation-dissipation relation $2\mathrm{Im}~ \chi(q,\omega) ={\omega }C(q,\omega)/{k_B T_{\text{eff}}(q)}$ with a scale-dependent effective temperature $T_{\rm eff}(q) \propto q^2$. These findings establish a striking exception to conventional paradigms of critical phenomena and illustrate how non-equilibrium forces can fundamentally reshape universality classes.

cond-mat.stat-mech↗

arXiv2025

Switching Dynamics of Metastable Open Quantum Systems

Classical metastability manifests as noise-driven switching between disjoint basins of attraction and slowing down of relaxation, quantum systems like qubits and Rydberg atoms exhibit analogous behavior through collective quantum jumps and long-lived Liouvillian modes with a small spectral gap. Though any metastable mode is expected to decay after a finite time, stochastic switching persists indefinitely. Here, we elaborate on the connection between switching dynamics and quantum metastability through the lens of the large deviation principles, spectral decomposition, and quantum-jump simulations. Specifically, we distinguish the trajectory-level noise-induced metastability (stochastic switching) from the spectrum-level deterministic metastability (small Liouvillian gap) in a Markovian open quantum system with bistability. Without stochastic switching, whether a small spectral gap leads to slow relaxation depends on initial states. In contrast, with switching, the memory of initial conditions is quickly lost, and the relaxation is limited by the rare switching between the metastable states. Consistent with the exponential scaling of the Liouvillian gap with system size, the switching rates conform to the Arrhenius law, with the inverse system size serving as the nonequilibrium analog of temperature. Using the dynamical path integral and the instanton approach, we further extend the connection between the quasipotential functional and the probabilities of rare fluctuations to the quantum realm. These results provide new insights into quantum bistability and the relaxation processes of strongly interacting, dissipative quantum systems far away from the thermodynamic limit.

quant-ph↗

arXiv2024

Activity-driven polymer knotting for macromolecular topology engineering

Macromolecules can gain special properties by adopting knotted conformations, but engineering knotted macromolecules is a challenging task. Here we surprisingly observed that knotting can be very effectively produced in active polymers. When one end of an actively reptative polymer is anchored, it can undergo continual self-knotting as a result of intermittent giant conformation fluctuations and the outward reptative motion. Once a knot is formed, it migrates to the anchored point due to a non-equilibrium ratchet effect. Moreover, when the active polymer is grafted on the end of a passive polymer, it can function as a self-propelling soft needle to either transfer its own knots to the passive polymer or directly braid knots on the passive polymer. We further show that these active needles can create inter-molecular bridging knots between two passive polymers. Our finding highlights the non-equilibrium effects in modifying the dynamic pathways of polymer systems, which have potential applications in macromolecular topology engineering, e.g., manipulating topological states of proteins and nucleic acids, as well as macromolecular braiding.

cond-mat.soft↗

arXiv2024

Self-Organized Time Crystal in Driven-Dissipative Quantum System

Continuous time crystals (CTCs) are characterized by sustained oscillations that break the time translation symmetry. Since the ruling out of equilibrium CTCs by no-go theorems, the emergence of such dynamical phases has been observed in various driven-dissipative quantum platforms. The current understanding of CTCs is mainly based on mean-field (MF) theories, which fail to address the problem of whether the long-range time crystalline order exists in noisy, spatially extended systems without the protection of all-to-all couplings. Here, we propose a new kind of CTC realized in a quantum contact model through self-organized bistability (SOB). The exotic CTCs stem from the interplay between collective dissipation induced by the first-order absorbing phase transitions (APTs) and slow constant driving provided by an incoherent pump. The stability of such oscillatory phases in finite dimensions under the action of intrinsic quantum fluctuations is scrutinized by the functional renormalization group method and numerical simulations. Occurring at the edge of quantum synchronization, the CTC phase exhibits an inherent period and amplitude with a coherence time diverging with system size, thus also constituting a boundary time crystal (BTC). Our results serve as a solid route towards self-protected CTCs in strongly interacting open systems.

quant-ph↗

arXiv2023

Non-Equilibrium Structural and Dynamic Behaviors of Polar Active Polymer Controlled by Head Activity

Thermodynamic behavior of polymer chains out of equilibrium is a fundamental problem in both polymer physics and biological physics. By using molecular dynamics simulation, we discover a general non-equilibrium mechanism that controls the conformation and dynamics of polar active polymer, i.e., head activity commands the overall chain activity, resulting in re-entrant swelling of active chains and non-monotonic variation of Flory exponent $ν$. These intriguing phenomena lie in the head-controlled railway motion of polar active polymer, from which two oppose non-equilibrium effects emerge, i.e., dynamic chain rigidity and the involution of chain conformation characterized by the negative bond vector correlation. The competition between these two effects determines the polymer configuration. Moreover, we identify several generic dynamic features of polar active polymers, i.e., linear decay of the end-to-end vector correlation function, polymer-size dependent crossover from ballistic to diffusive dynamics, and a polymer-length independent diffusion coefficient that is sensitive to head activity. A simple dynamic theory is proposed to faithfully explain these interesting dynamic phenomena. This sensitive structural and dynamical response of active polymer to its head activity provides us a practical way to control active-agents with applications in biomedical engineering.

cond-mat.soft↗