An open quantum battery (QB) model of a single qubit system charging in a coherent auxiliary bath (CAB) consisting of a series of independent coherent ancillae is considered. According to the collision charging protocol we derive a quantum master equation and obtain the analytical solution of QB in a steady state. We find that the full charging capacity (or the maximal extractable work (MEW)) of QB, in the weak QB-ancilla coupling limit, is positively correlated with the coherence magnitude of ancilla. Combining with the numerical simulations we compare with the charging properties of QB at finite coupling strength, such as the MEW, average charging power and the charging efficiency, when considering the bath to be a thermal auxiliary bath (TAB) and a CAB, respectively. We find that when the QB with CAB, in the weak coupling regime, is in fully charging, both its capacity and charging efficiency can go beyond its classical counterpart, and they increase with the increase of coherence magnitude of ancilla. In addition, the MEW of QB in the regime of relative strong coupling and strong coherent magnitude shows the oscillatory behavior with the charging time increasing, and the first peak value can even be larger than the full charging MEW of QB. This also leads to a much larger average charging power than that of QB with TAB in a short-time charging process. These features suggest that with the help of quantum coherence of CAB it becomes feasible to switch the charging schemes between the long-time slow charging protocol with large capacity and high efficiency and the short-time rapid charging protocol with highly charging power only by adjusting the coupling strength of QB-ancilla. This work clearly demonstrates that the quantum coherence of bath can not only serve as the role of “fuel” of QB to be utilized to improve the QB’s charging performance but also provide an alternative way to integrate the different charging protocols into a single QB.
An open quantum battery (QB) model of a single qubit system charging in a coherent auxiliary bath (CAB) consisting of a series of independent coherent ancillae is considered. According to the collision charging protocol we derive a quantum master equation and obtain the analytical solution of QB in a steady state. We find that the full charging capacity (or the maximal extractable work (MEW)) of QB, in the weak QB-ancilla coupling limit, is positively correlated with the coherence magnitude of ancilla. Combining with the numerical simulations we compare with the charging properties of QB at finite coupling strength, such as the MEW, average charging power and the charging efficiency, when considering the bath to be a thermal auxiliary bath (TAB) and a CAB, respectively. We find that when the QB with CAB, in the weak coupling regime, is in fully charging, both its capacity and charging efficiency can go beyond its classical counterpart, and they increase with the increase of coherence magnitude of ancilla. In addition, the MEW of QB in the regime of relative strong coupling and strong coherent magnitude shows the oscillatory behavior with the charging time increasing, and the first peak value can even be larger than the full charging MEW of QB. This also leads to a much larger average charging power than that of QB with TAB in a short-time charging process. These features suggest that with the help of quantum coherence of CAB it becomes feasible to switch the charging schemes between the long-time slow charging protocol with large capacity and high efficiency and the short-time rapid charging protocol with highly charging power only by adjusting the coupling strength of QB-ancilla. This work clearly demonstrates that the quantum coherence of bath can not only serve as the role of “fuel” of QB to be utilized to improve the QB’s charging performance but also provide an alternative way to integrate the different charging protocols into a single QB.
Recent theoretical and experimental protocols for the stable and effective charging of open quantum batteries (QBs), in particular adiabatic charging of three-level QBs via stimulated Raman adiabatic passages, have sparked renewed interest in adiabatic quantum dynamics. A central question is whether exploiting the adiabatic master equation could provide advantages over the previous studies in the effective charging of open QBs. To answer this question, we revisit the adiabatic charging of three-level QB by using the adiabatic quantum master equation formalism. We restrict ourselves to the weak-coupling regime with an Ohmic thermal bath and investigate the effects of relaxation and dephasing on the charging process. It is also worth emphasizing that our protocol to investigate the charging process of QBs based on the adiabatic master equation despite the previous studies is not phenomenological and is general. We analyze the dependence of the stored energy, ergotropy, as well as the efficiency of the QB on the total time of evolution t_{f}. We demonstrate that for very short charging time (t_{f}), where the evolution is highly nonadiabatic, the stored energy and ergotropy are very small. However, by increasing t_{f} we show that there is an optimal charging time t_{f}^{opt} in which, at low temperatures, we could fully charge the battery and effectively extract the entire amount of energy from it. Note that the optimal charging time could be decreased by adjusting the strength of the coupling between the system and environment and also be the appropriate choice of the Hamiltonian parameters, which, in turn, speed up the charging process. However, we show that for very long charging time t_{f} the charging energy, ergotropy, and efficiency decrease due to thermal excitations. Furthermore, to obtain more insights about the problem we investigate the distance between the density matrix of a system at optimal charging time t_{f}^{opt} and the corresponding thermal state by using the one-norm distance.
We revisit the adiabatic charging of a three-level QBs, using the adiabatic quantum master equation formalism. We restrict ourselves to the weak-coupling regime with an Ohmic thermal bath and investigate the effects of relaxation and dephasing on the charging process. We analyze the dependence of the stored energy, ergotropy as well as efficiency of QB on the total time of evolution tf. We demonstrate that for very short charging time (tf), where the evolution is highly non-adiabatic, the stored energy and ergotropy are very small. However, with increasing tf we show that there is an optimal charging time, tfopt, for maximum energy charging such that at low temperatures we could fully charge the battery and effectively extract the whole amount of energy from it. Note that, the optimal charging time could be decreased by adjusting strength of the coupling between system and environment and also appropriate choice of the Hamiltonian parameters which in turn speed up the charging process. On the other hand, we show that for very long charing time tf the charging energy, ergotropy and efficiency decrease due to thermal excitations. Furthermore to get more insights about the problem we investigate the distance between density matrix of system at optimal charging time tfopt and the corresponding thermal state using one-norm distance.
In the field of quantum thermodynamics, optimizing the performance of quantum battery (QB) under environmental effects remains a primary research interest. However, environmental control remains challenging due to its high-dimensional degrees of freedom, particularly in the non-Markovian regimes. This work investigates the charging dynamics of a QB model subjected to a tunable non-Markovian environment. We show that a controllable non-Markovian setting can be exploited to improve the QB's primary figure of merit. Specifically, we show that by tuning the relative ratio of QB-charger coupling strength and charger-bath coupling strength, the maximum dynamic values of the charging power, energy storage, and work extraction of QB can be significantly increased. Our findings suggest that employing non-Markovian effects in a tunable way offers a promising avenue for enhancing the performance of quantum thermodynamic devices, and sheds new light on the intersection between the reservior engneering and quantum thermodynamics.
We explore the wireless charging of a quantum battery (QB) via n 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.
In recent years, quantum battery (QB) models have emerged as crucial platforms for exploring the connections between quantum effects and energy within the framework of quantum thermodynamics. Inspired by the physical implementation of quantum switch (QS), we, in this work, present a simple QB model in which a two-level system as battery, under a series of coherent chargers, performs the indefinite causal order (ICO) charging by introducing a control qubit as QS. Within the energy-preserving collision interaction framework, we analyze the charging ICO and conventional definite causal order (DCO) dynamics, respectively, and discover the underlying connection between the final charged states of battery in ICO and DCO charging modes. That is, the ICO charged state can be understood as a split of the DCO charged state, accompanied by an offset caused by the interference component characterizing the ICO effect. That provides direct theoretical evidence that the ICO effect positively influences the ergotropy (i.e., the maximum extractable work) of QB only when quantum coherence is present in the charging process, and it is independent of the average stored energy of the QB. By combining numerical simulations, we examine that quantum coherence in our model is a strong quantum resource contributing to the ergotropy of QB, while the ICO effect plays a catalyst-like role, assisting quantum coherence in further enhancing the ergotropy of the battery. In addition, we also demonstrate that increasing the number of chargers also benefits the optimal ergotropy of QB. Finally, we reveal that, when the coherent chargers are subject to the dephasing channel, the ICO charging mode is more robust against dephasing noise than the DCO charging mode. This investigation deepens our understanding of quantum coherence and the ICO effect in the context of quantum thermodynamics.
We consider a collection of two level systems, such as qubits, embedded into a microwave cavity as a promising candidate for the realization of high power quantum batteries. In this perspective, the possibility to design devices where the conventional single-photon coupling is suppressed and the dominant interaction is mediated by two-photon processes is investigated, opening the way to an even further enhancement of the charging performance. By solving a Dicke model with both single- and two-photon coupling we determine the range of parameters where the latter unconventional interaction dominates the dynamics of the system leading to better performances both in the charging times and average charging power of the QB compared to the single-photon case. In addition, the scaling of the maximum stored energy, fluctuations and charging power with the finite number of qubits N is inspected. While the energy and fluctuations scale linearly with N, the quadratic growth of the average power leads to a relevant improvement of the charging performance of quantum batteries based on this scheme with respect to the purely single-photon coupling case. Moreover, it is shown that the charging process is progressively faster by increasing the coupling from the weak to the ultra-strong regime.