arXiv subjects

Fu-Quan Dou

Publications and source records attributed to Fu-Quan Dou.

At least 19 recordsLinked to original sources

arXiv2026

Quantum phase transitions of the Cavity Heisenberg spin-chain

The interplay between quantum criticality and ergodicity breaking constitutes a central challenge in complex quantum many-body systems. Here, we investigate ground-state quantum phase transitions (QPTs) and excited-state quantum phase transitions (ESQPTs), as well as ergodic-nonergodic transition in the cavity Heisenberg spin-chain (CHS) model. By combining quantum information measures with semiclassical fixed-point analysis, we identify a deformed phase that interpolates between the normal and superradiant phases, featuring a logarithmic nonanalyticity in the density of states (DoS) and two additional jump discontinuities. We further elucidate the spectral-structure mechanism underlying the connection between ESQPTs and the ergodic--nonergodic transition (ENET) via level statistics, participation ratios, and multifractal analysis. Our results provide a general framework for characterizing phase structures and spectral features in light--matter quantum many-body systems.

quant-ph↗

arXiv2026

Compactness, mass spectra, and strong stability of singly heavy tetraquarks

We propose a Coulomb-like parameterization in terms of bag radius of the short-range chromo-electric interaction between heavy quarks and strange quarks within the framework of the MIT bag model for hadrons including multiquark systems and re-examine mass spectra of doubly and fully heavy baryons self-consistently and variationally. Building upon this, we apply this approach to systematically investigate the mass spectra and $S$-wave strong decay stability of singly heavy tetraquark systems, including $nQ\bar{n}\bar{n}$, $nQ\bar{s}\bar{n}$, $Qs\bar{n}\bar{n}$, $sQ\bar{s}\bar{n}$, and $sQ\bar{s}\bar{s}$ (with $Q=c,b$). Choosing the bag confinement energy as a compactness criterion, the bag radius is shown to be close to the confinement uplimit of the radius, $R_c = 5.615\,\text{GeV}^{-1}$, for the compact singly charmed systems,and for these systems some high-spin states are unlikely to form compact structures, while several others do exhibit potential for compactnessNotably, computation indicates that the state $T_{nc\bar{s}\bar{n}}(0^+,2.925)$ emerges as a compact tetraquark with relatively large strong decay width, a plausible candidate of the observed tetrquark $T_{c\bar{s}0}^{a}(2900)$.

hep-ph↗

arXiv2026

Towards a nuclear isomer quantum battery

Quantum batteries (QBs) -- quantum devices governed by the principles of quantum mechanics -- hold great promise for next-generation energy storage. However, most existing research efforts focus on atomic or molecular systems featuring low-energy and short-lived energy levels, leaving the exploitation of high-energy, ultra-stable nuclear energy levels for energy storage as a critical unaddressed challenge. Here, we propose an innovative design of referred to as nuclear isomer quantum batteries (NIQBs), whose energy storage unit is typically composed of two-level and three-level nuclei incorporating nuclear isomers. The charging dynamics is driven by the interaction between the nuclear system and x-ray free electron laser (XFEL). Compared to QBs based on atomic systems, NIQBs deliver substantial performance enhancements, with stored energy and average charging power enhanced by factors of $10^{1}$--$10^{6}$ and $10^{6}$--$10^{11}$, respectively, and a markedly extended lifetime range spanning from microseconds to $10^5$ years. Notably, the vast majority of NIQBs enable complete energy extraction as their excited-state lifetimes exceed the laser-nuclear interaction time, rendering spontaneous emission negligible. The proposed NIQBs framework is compatible with diverse nuclear systems, enabling tailored nucleus selection for varied operating conditions. Our results provide a feasible pathway toward realizing high-performance QBs with superior energy-storage efficiency.

quant-ph↗

arXiv2026

Quantum battery optimized by parametric amplification

The parametric amplification enabled by two-photon driving constitutes a versatile platform for advanced quantum technologies. We present an optimized scheme for implementing quantum batteries (QBs) based on a superconducting circuit system, where a two-photon-driven LC resonator serves as the charger and an array of transmon qubits functions as the battery. Our results show that two-photon parametric driving exponentially enhances the effective cavity-qubit coupling, which in turn gives rise to near-degenerate energy-level structures and highly entangled quantum states. This significantly enhances the charging power and enables rapid energy transfer from the charger to the battery. Moreover, the engineered squeezed cavity mode and the associated quantum correlations effectively suppress environmentally induced decoherence, thereby delaying energy leakage and facilitating stable energy storage. The proposed scheme remains robust against practical experimental imperfections, such as parameter disorder and environmental noise, preserving its performance advantages. The work provides a feasible platform for realizing high-power, high-stability QBs and highlights the potential of parametric control in quantum energy technologies.

quant-ph↗

arXiv2025

Ergotropy in Quantum Batteries

Ergotropy--a key figure of merit for quantum battery (QB) performance--plays a crucial role. However, the dynamics and physical mechanisms governing ergotropy evolution remain open challenges. Here, we investigate the ergotropy of a general QB model and find that the charging process is accompanied by the variation and inversion of the energy level populations. In the absence of population inversion, the ergotropy is fully consistent with coherent ergotropy; in local and global population inversion, it is determined by both coherent and incoherent ergotropy. Via random sampling of quantum states and Hamiltonians, we show that coherence and the participation ratio enhance coherent ergotropy, whereas incoherent ergotropy--whether enhanced, unchanged, or suppressed--depends on diagonal entropy, the participation ratio, and energy level population ordering. We demonstrate that the ergotropy lower bound is incoherent ergotropy, the upper bound is the QB stored energy, and enhanced QB purity suppresses locked energy and boosts charging efficiency. Furthermore, we use the Tavis-Cummings (TC) and Jaynes-Cummings (JC) batteries as paradigms to validate our findings. Our work elucidates ergotropy underlying mechanisms in general QBs and establishes a rigorous framework for optimizing ergotropy and charging efficiency, paving the way for high-performance quantum energy-storage devices.

quant-ph↗

arXiv2025

Robust, fast, and efficient formation of stable tetratomic molecules from ultracold atoms via generalized stimulated Raman exact passage

The study of the conversion of ultracold atoms into molecules has long remained a hot topic in atomic, molecular, and optical physics. However, most prior research has focused on diatomic molecules, with relatively scarce exploration of polyatomic molecules. Here we propose a two-step strategy for the formation of stable ultracold tetratomic molecules. We first suggest a generalized nonlinear stimulated Raman exact passage (STIREP) technique for the coherent conversion of ultracold atoms to tetratomic molecules, which is subsequently followed by a chainwise-STIREP technique to transfer the resulting molecules into a sufficiently stable ground state. Through systematic numerical analysis, we demonstrate that the proposed two-step strategy holds great potential for the robust, fast, and efficient formation of stable ultracold tetratomic molecules.

cond-mat.quant-gas↗

arXiv2025

Resonant Singly Heavy Pentaquarks in the MIT Bag Model: Mass Spectra and Strong Decays

Exploring the limits of color interactions in multiquark states is an important topic. Based on the bag confinement picture of hadrons, we find that for singly heavy pentaquarks, the bag confinement radius precisely falls within the range of color interaction limits provided by lattice QCD, approximately 1.17--1.29$\,\text{fm}$. This leads us to believe that singly heavy pentaquark states have the potential to form resonant states. Inspired by singly heavy baryons, we consider the mirror pentaquarks of singly heavy baryons. Furthermore, we adopt the MIT bag model, taking into account chromomagnetic and color-electric interactions between heavy and strange quarks, to calculate the mass spectrum of singly heavy pentaquarks configured as $qqqQ\bar{q}$ and analyze the stability of their S-wave two-body strong decays. We show that for the singly heavy pentaquark system, the masses are generally about $500\, \text{MeV}$ higher than the corresponding mirror baryon ground state masses, which is consistent with conclusions drawn from chiral methods. We also provide a mass mapping relationship between singly heavy pentaquarks and singly heavy baryons based on light quark flavor symmetry. The analysis of strong decays indicates that these singly heavy pentaquarks are unstable with respect to strong decays, which is consistent with our initial hypothesis.

hep-ph↗

arXiv2025

Highly efficient nuclear population transfer through physics-informed neural networks

Nuclear coherent population transfer (NCPT) offers numerous potential applications, particularly in next-generation nuclear clocks and nuclear batteries. However, the realization of high fidelity, fast operation, and low energy consumption in NCPT remains so far challenging. Here, we employ physics-informed neural networks (PINNs) to the population transfer in an open three-level nuclear system with spontaneous emission. The method embeds the system's control equations and boundary conditions into the loss function, thereby enabling the automatic learning of optimal laser pulse sequences that drive highly efficient population transfer. We take a short-lived excited state of $^{172}\mathrm{Yb}$ and a long-lived state of $^{229}\mathrm{Th}$ as representative examples, and systematically compare the performance of the PINNs approach with three conventional control strategies. We show that PINNs can achieve higher transfer efficiency with smaller pulse areas and shorter durations across different lifetime regimes. Our results provide a new perspective to overcome the lifetime limitation and enhance the efficiency of nuclear state transfer.

nucl-th↗

arXiv2025

Noise-induced quantum synchronization of spin chain with periodic boundary

Quantum synchronization offers new possibilities for the exploration of collective dynamics in many-body systems. However, achieving synchronization in many-body quantum systems still faces numerous challenges. Here, we focus on the synchronization behavior of quantum spin chain with periodic boundary conditions under the influence of local Gaussian white noise. The necessary conditions for synchronization of local spin observables when noise acts on individual spin and two spins are obtained. The degree of synchronization between the expectation values of the local spin observables is characterized by utilizing the Pearson correlation coefficient, while the frequency of oscillation is determined through the application of fast Fourier transformation. We also discuss qualitatively the effect of system parameters on synchronization time. Despite the presence of noise leading to decoherence in the system, entanglement between synchronous and antisynchronous spins still persists. Our results provide valuable insights toward the realization of quantum synchronization in many-body quantum systems.

quant-ph↗

arXiv2025

Wireless energy transfer in non-Hermitian quantum battery

The extraction of energy is one of fundamental challenges in realizing quantum batteries (QBs). Here, we propose two wireless transfer schemes with parity-time symmetries to efficiently extract the energy stored in non-Hermitian QBs to consumption centers. For linear cases, the transfer energy oscillates periodically in the unbroken symmetry region and grows hyperbolically in the broken region. For nonlinear cases, the transfer energy eventually reach and remain steady-state values arising from the feedback mechanism of the nonlinear saturable gain. Furthermore, we show the significant robustness and the ultrafast response of the wireless transfer schemes to sudden movements around one metre. Our work overcomes energy bottlenecks for wireless transfer schemes in QBs and may provide inspirations for practical applications of QBs.

quant-ph↗

arXiv2025

Solitons in Bose-Einstein Condensates with Attractive Self-Interaction on a M\"obius Strip

We study the matter-wave solitons in Bose-Einstein condensate (BEC) trapped on a M\"{o}bius strip (MS), based on the respective Gross-Pitaevskii (GP) equation with the mean-field theory. In the linear regime, vortex states are characterized by quantum numbers, $n$ and $m$, corresponding to the transverse and circumferential directions, with the phase structure determined by the winding number (WN) $m$. Odd and even values of $n$ must associate, respectively, with integer and half-integer values of $m$, the latter ones requiring two cycles of motion around MS for returning to the initial phase. Using variational and numerical methods, we solve the GP equation with the attractive nonlinearity, producing a family of ground-state (GS) solitons for values of the norm below the critical one, above which the collapse sets in. Vortex solitons with $n=1,m=1$ and $% n=2,m=1/2$ are obtained in a numerical form. The vortex solitons with $% n=1,m=1$ are almost uniformly distributed in the azimuthal direction, while ones with $n=2,m=1/2$ form localized states. The Vakhitov-Kolokolov criterion and linear-stability analysis for the GS soliton solutions and vortices with $n=1,m=1$ demonstrates that they are completely stable, while the localized states with $n=2,m=1/2$ are completely unstable. Finally, the motion of solitons on the MS and the collision of two solitons are discussed.

nlin.PS↗

arXiv2025

Searching for compact pentaquark state within the bag model framework

The search for the compact limit of multi-quark states is a challenging issue. Within the framework of the MIT bag model, we propose an effective limit bag radius of $R_{c} = 5.615 \, \text{GeV}^{-1}$(or $1.11 \, \text{fm}$) for bound states . When the bag radius of a hadron falls below this value, the bag binding energy satisfies $E_{B} < 0$, indicating that the system has a compact intention. We consider various combinations of different numbers and ratios of heavy and light quarks, indicating that the bag radius of hadrons depending on the number of quarks is suppressed by the presence of heavy quarks. Focusing on five-quark combinations, we find that the average bag radius of $nncc\bar{c}$ is below the threshold $R_{c}$. We take into account color-magnetic interactions and calculate the mass, magnetic moment, binding energy, and relative strong decay width for the $nnQQ\bar{Q}$ system. We show that the binding energies of most states in the flavor combination $nncc\bar{c}$ are approximately $-20 \, \text{MeV}$, whereas states involving bottom quarks have binding energies around $-120 \, \text{MeV}$, with some decay widths suppressed by the decay constant. Additionally, the $nQQQ\bar{Q}$ system exhibits even deeper binding. Our results support the compact intention of $nnQQ\bar{Q}$ and suggest that the $nQQQ\bar{Q}$ configuration demonstrates even stronger compactness.

hep-ph↗

arXiv2024

Cavity-Heisenberg spin-$j$ chain quantum battery and reinforcement learning optimization

Machine learning offers a promising methodology to tackle complex challenges in quantum physics. In the realm of quantum batteries (QBs), model construction and performance optimization are central tasks. Here, we propose a cavity-Heisenberg spin chain quantum battery (QB) model with spin-$j (j=1/2,1,3/2)$ and investigate the charging performance under both closed and open quantum cases, considering spin-spin interactions, ambient temperature, and cavity dissipation. It is shown that the charging energy and power of QB are significantly improved with the spin size. By employing a reinforcement learning algorithm to modulate the cavity-battery coupling, we further optimize the QB performance, enabling the stored energy to approach, even exceed its upper bound in the absence of spin-spin interaction. We analyze the optimization mechanism and find an intrinsic relationship between cavity-spin entanglement and charging performance: increased entanglement enhances the charging energy in closed systems, whereas the opposite effect occurs in open systems. Our results provide a possible scheme for design and optimization of QBs.

quant-ph↗

arXiv2024

Ground-state phase transitions in spin-1 Bose-Einstein condensates with spin-orbit coupling

We investigate phase transitions of the ground state (GS) of spin-1 Bose-Einstein condensates under the combined action of the spin-orbit coupling (SOC) and gradient magnetic field. Introducing appropariate raising and lowering operators, we exactly solve the linear system. Analyzing the obtained energy spectrum, we conclude that simultaneous variation of the magnetic-field gradient and SOC strength leads to the transition of excited states into the GS. As a result, any excited state can transition to the GS, at appropriate values of the system's parameters. The nonlinear system is solved numerically, showing that the GS phase transition, similar to the one in the linear system, still exists under the action of the repulsive nonlinearity. In the case of weak attraction, a mixed state appears near the GS transition point, while the GS transitions into an edge state under the action of strong attractive interaction.

cond-mat.quant-gas↗

arXiv2024

Microwave-activated two-qubit gates for fixed-coupling and fixed-frequency transmon qubits

All-microwave control of fixed-frequency superconducting quantum systems offers the potential to reduce control circuit complexity and increase system coherence. Nevertheless, due to the limited control flexibility in qubit parameters, one has to address several issues, such as quantum crosstalk and frequency crowding, for scaling up qubit architecture with non-tunable elements. This study proposes a microwave-activated two-qubit gate scheme for two fixed-frequency transmon qubits coupled via a fixed-frequency transmon coupler. The protocol relies on applying a microwave pulse exclusively to the coupler, enabling the implementation of a controlled-Z (CZ) gate. We show that the gate fidelity exceeding 0.999 can be achieved within 150 ns, excluding decoherence effects. Moreover, we also show that leakage from the computational subspace to non-computational states can also be effectively suppressed.

quant-ph↗

arXiv2024

High-fidelity Nuclear Coherent Population Transfer via the Mixed-State Inverse Engineering

Nuclear coherent population transfer (NCPT) plays an important role in the exploration and application of atomic nuclei. How to achieve high-fidelity NCPT remains so far challenging. Here, we investigate the complete population transfer of nuclear states. We first consider a cyclic three-level system, based on the mixed-state inverse engineering scheme by adding additional laser fields in an open three-level nuclear system with spontaneous emission. We find the amplitude of the additional field is related to the ratio of the pump and Stokes field amplitudes. As long as an appropriate additional field is selected, complete transfer can be achieved even when the intensities of the pump and Stokes fields are exceedingly low. The transfer efficiency exhibits excellent robustness with respect to laser peak intensity and pulse delay. We demonstrate the effectiveness through examples such as $^{229}$Th, $^{223}$Ra, $^{113}$Cd, and $^{97}$Tc, which have a long lifetime excited state, as well as $^{187}$Re, $^{172}$Yb, $^{168}$Er and $^{154}$Gd with a short lifetime excited state. Focusing on the case without additional coupling, we further reduce the three-level system to an effective two-level problem. We modify the pump and Stokes pulses by using counterdiabatic driving to implement high-fidelity population transfer. The schemes open up new possibilities for controlling nuclear states.

nucl-th↗

arXiv2023

Resonator-qutrits quantum battery

Quantum batteries (QBs) are energy storage and transfer microdevices that open up new possibilities in energy technology. Here, we derive a resonator-qutrits quantum battery (QB) model consisting of a multi-modes resonator and $N$ superconducting transmon qutrits. We investigate the charging and self-discharging performance of the QB and discuss the roles of quantum coherence and quantum entanglement. The results show that environment noise is not always detrimental for QB systems. The QB with efficient charging, stable energy-storage and slow self-discharging processes can be realized by considering the dephasing noise and manipulating the energy gap. We find that the charing energy is positively related to coherence and entanglement while the stable energy and the self-discharing energy are negatively related to coherence. The phenomenon of the vanishing entanglement corresponds to the dynamic decoupling behavior of the QB's steady states. Our results provide a way to realize many-body QBs on superconducting circuits platform.

quant-ph↗

arXiv2023

Three-level Dicke quantum battery

Quantum battery (QB) is the energy storage and extraction device that is governed by the principles of quantum mechanics. Here we propose a three-level Dicke QB and investigate its charging process by considering three quantum optical states: a Fock state, a coherent state, and a squeezed state. The performance of the QB in a coherent state is substantially improved compared to a Fock and squeezed states. We find that the locked energy is positively related to the entanglement between the charger and the battery, and diminishing the entanglement leads to the enhancement of the ergotropy. We demonstrate the QB system is asymptotically free as $N \rightarrow \infty$. The stored energy becomes fully extractable when $N=10$, and the charging power follows the consistent behavior as the stored energy, independent of the initial state of the charger.

quant-ph↗