Abstract In this paper, we study the performance of a quantum battery composed of three non-interacting central qubits, which are charged through interactions with three distinct thermal baths, each bath consisting of interacting qubits. We utilize the Holstein-Primakoff transformation and thermodynamic limits to map the collective spin operators of the baths to bosonic modes. Additionally, we employ the finite trio coherent state as the initial state for the charging process to explore its impact on the overall system performance. The study focuses on evaluating the stored energy efficiency and the entropy of the charger modes to assess the overall charging performance. By examining the system parameters such as anisotropy, dimension and shift parameters, and the intensity of the trio coherent state, the optimal conditions for efficient energy storage are identified. Our results provided the role of thermodynamic processes and quantum correlations in enhancing the performance of our quantum battery model.
Abstract In this paper, we study the performance of a quantum battery composed of three non-interacting central qubits, which are charged through interactions with three distinct thermal baths, each bath consisting of interacting qubits. We utilize the Holstein-Primakoff transformation and thermodynamic limits to map the collective spin operators of the baths to bosonic modes. Additionally, we employ the finite trio coherent state as the initial state for the charging process to explore its impact on the overall system performance. The study focuses on evaluating the stored energy efficiency and the entropy of the charger modes to assess the overall charging performance. By examining the system parameters such as anisotropy, dimension and shift parameters, and the intensity of the trio coherent state, the optimal conditions for efficient energy storage are identified. Our results provided the role of thermodynamic processes and quantum correlations in enhancing the performance of our quantum battery model.
Quantum batteries (QBs) exploit principles of quantum mechanics to accelerate the charging process and aim to achieve optimal energy storage. However, analytical results for investigating these problems remain lacking due to the challenges associated with nonequilibrium dynamics. In this work we analytically investigate a central-spin QB model in which Nb spin-21 battery cells interact with Nc spin-21 charger units, using m initially excited charger units as a resource. By employing the invariant subspace method and the shifted Holstein-Primakoff transformation, we identify four scenarios in which optimal energy storage can be achieved: (i) ${N}_{b}\ensuremath{\ll}m\ensuremath{\ll}{N}_{c}$, (ii) $m\ensuremath{\ll}{N}_{b}\ensuremath{\ll}{N}_{c}$, (iii) $m\ensuremath{\ll}{N}_{c}\ensuremath{\ll}{N}_{b}$, and (iv) ${N}_{b}\ensuremath{\ll}m=k{N}_{c} [k\ensuremath{\in}(0,1)]$. In these cases, optimal storage is ensured by the SU(2) symmetry emerging from the charging dynamics. The first three cases map the central-spin QB to different Tavis-Cummings (TC) QBs, while the fourth corresponds to the non-TC limit. We analytically determine the charging time and demonstrate that in the fully charging cases (i) and (iv), the collective charging exhibits an Nb-fold enhancement in speedup compared to the parallel charging scheme. Additionally, we numerically observe a unified charging behavior when m=Nc, showing that asymptotically optimal energy storage is possible when Nb=m=Nc. In this case, we find a collective charging enhancement scaling as Nb0.8264. The origin of the collective charging advantage in central-spin quantum batteries is also analyzed through the quantum speed limit and a multipartite entanglement witness. Our results highlight the crucial role of dynamically emergent SU(2) symmetry in providing an analytical understanding of nonequilibrium charging dynamics in QBs.
Quantum batteries have emerged as promising platforms for exploring energy storage and transfer processes governed by quantum mechanical laws. In this work, we study three models of two-qubit open quantum systems. The first model comprises two central spins immersed in spin baths, and both central spins are collectively considered as quantum batteries. The impact of inter-qubit interactions on the performance of the quantum battery is investigated. In the second model, a two-qubit model interacting with a squeezed thermal bath serves as a collective quantum battery, where the impact of inter-atomic distance and the bath temperature on the battery's performance is explored. Furthermore, a two-qubit model is used, where one qubit is modeled as a battery and the other as a charger. The charger in this model interacts with an anisotropic spin-chain bath, which is conducive to quantum criticality. It is demonstrated that this criticality has a substantial impact on the quantum battery's storage capacity.
In this work, we investigate the autonomous charging process of a quantum battery coupled to a structured reservoir composed of two qubits, each locally coupled to its own bosonic thermal bath. Moreover, the reservoir interacts with a charger-battery architecture through three configurations: (I) direct coupling between reservoir qubits and battery; (II) collective coupling among the reservoir qubits, charger, and battery; and (III) a collective coupling between the reservoir qubits and charger together with a local charger-battery interaction. However, by using incoherent and coherent initial states, we analyze the stored energy, ergotropy, and charging power of the battery, and derive upper and lower bounds on the extractable work in terms of the free energy of coherence and the correlations exchanged between subsystems. Our results show that global and local coherences, as well as total correlations, act as quantum resources that enhance autonomous charging. Additionally, we demonstrate that the free energy stored in the quantum battery splits into contributions from coherence and correlations, providing numerical evidence that supports the derived ergotropy bounds. Importantly, this work highlights how structured reservoirs enable autonomous and resource-enhanced quantum battery operation.
Quantum batteries represent a new and promising technological application of quantum mechanics, offering the potential for enhanced energy storage and fast charging. In this work, we study a quantum battery composed of three two-level systems with XXZ coupling operating under open boundary conditions. We investigate the role played by ferromagnetic and antiferromagnetic initial configurations on the charging dynamics of the battery. Two charging mechanisms are explored: static charging, where the battery interacts with a constant classical external field, and harmonic charging, where the field oscillates periodically over time. Our results demonstrate that static charging can be more efficient in the ferromagnetic case, achieving maximum energy due to complete population inversion between the ground and excited states. In contrast, harmonic charging excels in the antiferromagnetic case. By analyzing the stored energy and the average charging power in these two regimes, we highlight the impact of anisotropy on the performance of quantum batteries. Our findings provide valuable insights for optimizing quantum battery performance based on the system's initial state and coupling configuration, paving the way for the study of more efficient quantum devices for energy storage.
Quantum battery works as a micro- or nanodevice to store and redistribute energy at the quantum level. Here we propose a spin-charger protocol, in which the battery cells are charged by a finite number of spins through a general Heisenberg XY interaction. Under the isotropic interaction, the spin-charger protocol is endowed with a higher capacity in terms of the maximum stored energy than the conventional protocols, where the battery is charged by a continuous-variable system, e.g., a cavity mode. By tuning the charger size, a tradeoff between the maximum stored energy and the average charging power is found in comparison to the cavity-charger protocol in the Tavis-Cummings model. Quantum advantage of our protocol is manifested by the scaling behavior of the optimal average power with respect to the battery size, in comparing the collective charging scheme to its parallel counterpart. We also discuss the detrimental effect on the charging performance from the anisotropic interaction between the battery and the charger, the nonideal initial states for both of them, and the crosstalk among the charger spins. A strong charger-charger interaction can be used to decouple the battery and the charger. Our findings about the advantages of the spin-charger protocol over the conventional cavity-charger protocols, including the high capacity of energy storage and the superior power law in the collective charging, provide an insight to exploit an efficient quantum battery based on the spin-spin-environment model.
We study the energy-transfer process in quantum battery systems consisting of multiple central spins and bath spins. Here with ``quantum battery'' we refer to the central spins, whereas the bath serves as the ``charger.'' For the single-central-spin battery, we analytically derive the time evolutions of the energy transfer and the charging power with arbitrary number of bath spins. For the case of multiple central spins in the battery, we find the scaling-law relation between the maximum power Pmax and the number of central spins NB. It approximately satisfies a scaling law relation ${P}_{\mathrm{max}}\ensuremath{\propto}{N}_{B}^{\ensuremath{\alpha}}$, where scaling exponent $\ensuremath{\alpha}$ varies with the bath spin number N from the lower bound $\ensuremath{\alpha}=1/2$ to the upper bound $\ensuremath{\alpha}=3/2$. The lower and upper bounds correspond to the limits $N\ensuremath{\rightarrow}1$ and $N\ensuremath{\gg}{N}_{B}$, respectively. In thermodynamic limit, by applying the Holstein-Primakoff transformation, we rigorously prove that the upper bound is Pmax=0.72BANNB3/2, which shows the same advantage in scaling of a recent charging protocol based on the Tavis-Cummings model. Here B and A are the external magnetic field and coupling constant between the battery and the charger.