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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., Comment: 10 pages, 13 figures

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., Comment: to be published in Physical Review A

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.

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., Comment: 9 pages,7 figures

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., Comment: 9 pages, 5 figures. Comments are welcome

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., Comment: 9 Pages, 9 Figures

Quantum batteries are energy storage devices that satisfy quantum mechanical principles. How to obtain analytical solutions for quantum battery systems and achieve a full charging is a crucial element of the quantum battery. Here, we investigate the Rosen-Zener Quantum batteries are energy storage devices that satisfy quantum mechanical principles. How to obtain analytical solutions for quantum battery systems and achieve a full charging is a crucial element of the quantum battery. Here, we investigate the Rosen-Zener quantum battery with $N$ two-level systems, which includes atomic interactions and external driving field. The analytical solutions of the stored energy, changing power, energy quantum fluctuations, and von Neumann entropy (diagonal entropy) are derived by employing the gauge transformation. We demonstrate that full charging process can be achieved when the external driving field strength and scanning period conforms to a quantitative relationship. The local maximum value of the final stored energy corresponds to the local minimum values of the final energy fluctuations and diagonal entropy. Moreover, we find that the atomic interaction induces the quantum phase transition and the maximum stored energy of the quantum battery reaches the maximum value near the quantum phase transition point. Our result provides an insightful theoretical scheme to realize the efficient quantum battery., Comment: 10 pages,7 figures. Accepted in Physical Review A

We investigate the adiabatic evolution of light in nonlinear waveguide couplers via resonance-locked inverse engineering based on stimulated Raman adiabatic passage (STIRAP). The longitudinal varying detunings of the propagation coefficients are designed to eliminate dynamically the nonlinear effect, which induce the non-adiabatic oscillations. We show that different light evolutions such as complete light transfer, light split and light return can be realized adiabatically with appropriate choices of the detunings even in the nonlinear regime. The features open new opportunities for the realization of all-optical nonlinear devices with high fidelity in integrated optics., Comment: 8 pages,6 figures

Quantum battery (QB) is the miniature energy storage and release device and plays a crucial role in future quantum technology. Here, an implementation scheme of a QB is proposed on a superconducting circuit which is composed by $N$ coupled transmon qubits and a one-dimensional transmission line resonator. We derive the Hamiltonian of the QB system and investigate its charging performance by considering three decay channels. We find that the presence of the decay channels suppresses the high oscillation of the energy storage process, thereby realizing a stable and powerful QB. In particular, compared with the resonator decay and the qubit relaxation, the qubit dephasing shows a counterintuitive advantage in our QB. We show that the nearest neighbor interaction always have a positive impact on the stable energy and the coupling only significantly influences the maximum charging power in the fully nondegenerate ground state region. We also demonstrate the feasibility of our approach by evaluating the QB performance under experimental parameters., Comment: 10 pages, 7 figures

We investigate the performance of the Lipkin-Meshkov-Glick quantum battery based on shortcuts to adiabaticity (STA). We mainly consider the situation where the coupling strength of any two sites in the quantum battery is a sinusoidal function with respect to time. The charging efficiency of the quantum battery can be greatly enhanced via STA. We also analyze the influences of parameters, including particle number, anisotropic parameter, the amplitude and frequency of the driving fields. It is found that an efficient charging process and thus high charging advantages can be achieved by adjusting these parameters properly. Moreover, we calculate the energy fluctuation, von Neumann entropy and energy cost during charging. The STA can make the stored energy and the von Neumann entropy change periodically during the charging process and reduce the energy fluctuation, and the minimal energy fluctuation always occurs in the proximity of minima of the von Neumann entropy., Comment: 8 pages,5 figures

According to the Heisenberg uncertainty principle between time and energy fluctuation, a concept of the quantum speed limit (QSL) has been established to determine the minimum evolutionary time between quantum states. Considerable theoretical and experimental efforts are invested in obtaining the QSL time bounds in various scenarios. However, it remains a long-standing goal to derive a meaningful QSL bound for a general quantum problem. Here, we propose a geometrical approach to derive a QSL bound for closed and open quantum systems. By solving a quantum brachistochrone problem in the framework of the Riemannian metric, we show that the QSL between a given initial state to a final state is determined not only by the entire dynamics of the system but also by the individual dynamics of a critical parameter. We exemplify the utility of the new bound in three representative scenarios, demonstrating a pronounced advantage in finding a tight and meaningful QSL bound of a general quantum evolution problem., Comment: 10 pages,4 figures

We propose a cavity-Heisenberg spin chain (CHS) quantum battery (QB) with the long-range interactions and investigate its charging process. The performance of the CHS QB is substantially improved compared to the Heisenberg spin chain (HS) QB. When the number of spins $N \gg 1$, the quantum advantage $\alpha$ of the QB's maximum charging power can be obtained, which approximately satisfies a superlinear scaling relation $P_{max} \propto N^{\alpha}$. For the CHS QB, $\alpha$ can reach and even exceed $1.5$, while the HS QB can only reach about $\alpha=0.75$. We find that the maximum stored energy of the CHS QB has a critical phenomenon. By analyzing the Wigner function, von Neumann entropy, and logarithmic negativity, we demonstrate that entanglement can be a necessary ingredient for QB to store more energy, but not sufficient.

We investigate high-fidelity multiple beam splitting in Hermitian and non-Hermitian symmetric coupled waveguides with one input and 2N output waveguide channels. In Hermitian systems, we realize adiabatically light splitting in resonant case based on the stimulated Raman adiabatic passage (STIRAP) and arbitrary proportion from the middle waveguide to outer waveguides in propagation coefficients mismatch case using shortcuts to adiabaticity (STA) technique. In non-Hermitian systems with even waveguides being dissipative, the compact and robust beam splitting can be achieved by eliminating the non-adiabatic coupling via the non-Hermitian STA method. We further verify the feasibility of our theoretical predictions by means of the beam propagation method (BPM). The suggested multiple beam splitters open new opportunities for the realization of on-chip high-bandwidth photonics with high fidelity in short distances., Comment: Accepted

We investigate the charging process of quantum battery (QB) systems in an extended Dicke model with both atomic interactions and an external driving field. We focus on the effects of the atomic interaction and the external driving field on the charging performance of QB and find that the maximum stored energy of QB has a critical phenomenon. We analyze the critical behavior and obtain the analytical expression of the critical atomic interaction. The dependence of the maximum stored energy, the energy quantum fluctuations and the maximum charging power on the number $N$ of the two-level systems are also discussed. In particular, for the maximum charging power, we obtain the quantum advantage of the QB, which approximately satisfies a superlinear scaling relation $P_{max}\propto N^{\alpha}$, where scaling exponent $\alpha$ varies with the number $N$ of the two-level systems. In the ultra-strong coupling regime, the atomic interaction can lead to a faster battery charging, and the quantum advantage $\alpha = 1.88$ can be achieved. While in the deep-strong coupling regime, the quantum advantage of the QB's maximum charging power is the same as that of the Dicke QB, i.e., $\alpha=1.5$.

The Su-Schrieffer-Heeger (SSH) model has recently received considerable attention in condensed matter because it describes a typical one-dimensional system with topological edge states. Here, we investigate SSH-based charging protocols of quantum batteries (QB) with N quantum cells. This SSH QB hopping interaction induced ground state splitting makes the different effects of the dimerize parameter to the QB in the different quantum phase region. In the non-splitting region, the dimerize parameter has little influence on the QB. Whereas the fully-splitting region, the dimerize parameter has a significantly quantum advantage to the energy and ergotropy in the ground state fully splitting region, which leads the dimerize spin couples will have larger occupations than other spins. Although we have enhanced energy and ergotropy by the dimerize parameter, QB's capacity will decrease.

Quantum batteries are energy storage devices that satisfy quantum mechanical principles. How to improve the battery's performance such as stored energy and power is a crucial element in the quantum battery. Here, we investigate the charging and discharging dynamics of a three-level counterdiabatic stimulated Raman adiabatic passage quantum battery via shortcuts to adiabaticity, which can compensate for undesired transitions to realize a fast adiabatic evolution through the application of an additional control field to an initial Hamiltonian. The scheme can significantly speed up the charging and discharging processes of a three-level quantum battery and obtain more stored energy and higher power compared with the original stimulated Raman adiabatic passage. We explore the effect of both the amplitude and the delay time of driving fields on the performances of the quantum battery. Possible experimental implementation in superconducting circuit and nitrogen-vacancy center is also discussed.

A quantum battery is a temporary energy-storage system. We constructed the quantum battery model of an N-spin chain with nearest-neighbor hopping interaction and investigated the charging process of the quantum battery. We obtained the maximum energy in the quantum battery charged by a coherent cavity driving field or a thermal heat bath. We confirmed that for a finite-length spin chain, thermal charging results in a nonzero ergotropy, contradicting a previous result: that an incoherent heat source cannot charge a single-spin quantum battery. The nearest-neighbor hopping interaction induces energy band splitting, which enhances the energy storage and the ergotropy of the quantum battery. We found a critical point in the energy and ergotropy resulting from the ground-state quantum phase transition, after which the energy significantly enhance. Finally, we also found that disorder increased the energy of the quantum battery.

Quantum batteries are energy storage or extract devices in a quantum system. Here, we present a closed-loop quantum battery by utilizing a closed-loop three-state quantum system in which the population dynamics depends on the three control fields and associated phases. We investigate the charging process of the closed-loop three-level quantum battery. The charging performance is greatly improved due to existence of the third field in the system to form a closed-contour interaction. Through selecting an appropriate the third control field, the maximum average power can be increased, even far beyond the most ideal maximum power value of non-closed-loop three-level quantum battery (corresponding to the most powerful charging obtainable with minimum quantum speed limit time and the maximum charging energy). We study the effect of global driving-field phase on the charging process and find the maximum extractable work (`ergotropy') and charging power vary periodically under different control field, with a period of $2\pi$. Possible experimental implementation in nitrogen-vacancy spin is discussed.