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arXiv:2406.18258 · Physical Review A

Sunburst quantum Ising battery

Akash Mitra, Shashi C. L. Srivastava

Published Jul 26, 2024• 13 citations
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Abstract

We study the energy-transfer process in the recently proposed sunburst quantum Ising model, which consists of two interacting integrable systems: a transverse Ising chain with a very small transverse field and a finite number of external isolated qubits. We show that in this model of the quantum battery, coupling between the battery and charger can be used to optimize the ergotropy, which is the maximum amount of energy that can be extracted from the battery. At the same time, maximum charging power increases with the coupling strength, allowing for the simultaneous optimization of both ergotropy and charging power in the strong-coupling limit. Furthermore, we show that both ergotropy and charging power are independent of the initial state of the charger.

DOI
10.1103/physreva.110.012227

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We study the energy-transfer process in the recently proposed sunburst quantum Ising model, which consists of two interacting integrable systems: a transverse Ising chain with a very small transverse field and a finite number of external isolated qubits. We show that in this model of the quantum battery, coupling between the battery and charger can be used to optimize the ergotropy, which is the maximum amount of energy that can be extracted from the battery. At the same time, maximum charging power increases with the coupling strength, allowing for the simultaneous optimization of both ergotropy and charging power in the strong-coupling limit. Furthermore, we show that both ergotropy and charging power are independent of the initial state of the charger.
Most quantum batteries studied so far with notable exception of Sachdev-Ye-Kitaev (SYK) batteries are based on integrable models, where superlinear scaling of charging power and hence a quantum advantage can be achieved, but at the cost of unstable stored energy due to integrability. Here, by considering the sunburst quantum Ising battery driven by periodic delta-kicks, we show that in the quantum chaotic regime a quantum advantage is achieved for number of batteries nb≤4n_b\leq 4nb​≤4, together with excellent stability of energy storage. In the integrable regime optimal energy storage and extraction are possible irrespective of the initial state of the charger. Finally, we show that the observed advantage does not originate from multipartite entanglement within the battery subsystem and is therefore classical in nature.
We discuss a one-dimensional coupled qubit-array quantum battery model under Born-Karman boundary conditions and investigate both the charging and discharging processes. Applying the stored energy, charging power, and ergotropy as the essential physical indicators of quantum battery, it is observed that minimizing the hopping interaction between the nearest-neighbor qubits in the qubit-array and increasing the number of qubits during battery setup are crucial. Additionally, we employ a classical driving field to optimize battery performance and explore the optimal quantum battery performance by adjusting the driving strength of the classical field. Finally, we have discovered that the initial energy in the charger no longer needs to be higher than the energy in the battery in our protocol, the charger will continue to supply energy to the battery even when there is limited initial available energy in the charger. And the conventional approach of preparing the battery's initial state in its ground state, as observed in previous studies, may not necessarily be the optimal choice. By introducing a strong classical driving field, it is possible to enhance energy storage by allowing for an initial presence of some energy within the battery.
We examine how a finite many-body system can function as an effective charger for a single-qubit quantum battery, using the Lipkin-Meshkov-Glick model as a paradigmatic setting. As our figure of merit, we consider the battery ergotropy while explicitly resolving the energetic flows across the composite system. In the absence of intra-charger interactions, we show that the generation of non-zero ergotropy is controlled by the competition between collective coupling and spectral mismatch. We further demonstrate that even passive positive-temperature charger states can generate finite battery ergotropy, provided the charger is sufficiently large and sufficiently hot. Intra-charger interactions restructure the charger spectrum and qualitatively modify the available energetic pathways. While they can enhance the amount of energy accessible for charging, they can simultaneously divert energy into internal many-body and battery-charger interaction channels, producing an energetic impedance to direct charger-to-battery transfer. Consequently, battery ergotropy alone is insufficient to characterize an effective many-body charger: the useful work generated and its energetic provenance must be assessed together.
This paper discusses the evolving dynamics of a quantum battery (QB) model consisting of two qubits interacting with a cavity field via multi-photon transitions. Employing the Lindblad master equation to account for dissipative effects, we investigated energy charging, charging power, ergotropy, and energy fluctuations to ascertain optimal conditions for efficient energy storage and extraction. Our results elucidate that lower photon numbers and moderate coherent state result in higher energy peaks and more stable storage. The charging power underscores the significance of maximizing initial energy transfer rates while mitigating rapid power decay. Ergotropy, representing the maximum extractable energy, is highly sensitive to dissipation rates, with elevated photon numbers enhancing charging efficiency but reducing stability. Energy fluctuation reveals that systems with higher photon numbers exhibit greater instability, emphasizing the necessity for controlling dissipation to preserve energy stability.
We explore the wireless charging of a quantum battery (QB) via nnn charging units, whose coupling is mediated by a common bosonic reservoir. We consider the general scenarios in which the charger energy is not maximal and the QB has residual ergotropy initially. It is found that the charging performance improves with the increase of the coupling strength. In the strong coupling regime, the charging time is insensitive to the charger energy, the number of charging units, and the residual ergotropy in the QB, while the ergotropy charged on the QB strongly depends on the charger energy and ergotropy, and the residual ergotropy in the QB does not help to enhance its performance. Moreover, the multiple charging units help to enhance the charging performance in the weak and moderate coupling regimes, while they are less efficient in the strong coupling regime.
We derive a quantum speed limit for ergotropy charging in the NNN-qubit Dicke battery. With the qubits initially in their ground state and the charger in a coherent state of mean photon number nˉ\bar{n}nˉ, the charging time to a target fraction ε\varepsilonε of the maximum extractable work obeys, in the classical-field limit, ΓNτ∗(ε)≥arcsin⁡εΓ_N τ^{*}(\varepsilon) \geq \arcsin\sqrt{\varepsilon}ΓN​τ∗(ε)≥arcsinε​, where ΓN=2λnˉ/NΓ_N = 2λ\sqrt{\bar{n}/N}ΓN​=2λnˉ/N​ is a single rate combining the light-matter coupling, the charger amplitude and the system size. The bound is geometric: although the ergotropy is defined by an optimisation over unitaries, it reduces to a fixed function of the angle swept by the collective spin on the Bloch sphere, and the drive bounds the rate at which that angle can grow, so the charging time is at least the required arc divided by the maximum angular velocity. The reduction rests on an exact statement about work extraction: only the coherent component of the drive delivers extractable work, while its vacuum fluctuations deposit energy that remains locked in the passive state. This makes the short-time coefficient independent of the charger occupation, and it is what separates a bound on extractable work from a bound on stored energy, which no instantaneous-power argument can supply. At finite charger occupation the inequality is tested rather than proved: numerical integration of the full Dicke Hamiltonian, with a dynamical charger and a mixed battery state, finds the bound respected at every admitted charging time for two to five qubits, and approached most closely in the limit of small target work. The familiar square-root estimate is the chord to this arc, recovered in the small-angle limit and weaker whenever a large fraction of the maximum work is required.