Thermally charged quantum batteries provide a stable and easy-to-have energy resource, but remain passive and therefore do not allow useful energy extraction on demand via unitary operations. We introduce a time-dependent stirring protocol that activates a thermally charged quantum battery through a time-dependent coupling to an auxiliary activator, thereby generating correlations that drive the battery into an active state. Accounting explicitly for the energetic cost of the stirring process, the entropic cost of correlation generation and the activation time, we derive bounds on the maximal net extractable energy. Incorporating projective measurement on the activator and exploiting the information gained through the measurement further enhances the extractable energy. As an experimentally relevant example, we analyze a waveguide-QED setup where a harmonic-oscillator battery (waveguide) is stirred and monitored by a two-level system. We characterize the performance of the protocol in terms of net extractable energy (net ergotropy) and power output.
Thermally charged quantum batteries provide a stable and easy-to-have energy resource, but remain passive and therefore do not allow useful energy extraction on demand via unitary operations. We introduce a time-dependent stirring protocol that activates a thermally charged quantum battery through a time-dependent coupling to an auxiliary activator, thereby generating correlations that drive the battery into an active state. Accounting explicitly for the energetic cost of the stirring process, the entropic cost of correlation generation and the activation time, we derive bounds on the maximal net extractable energy. Incorporating projective measurement on the activator and exploiting the information gained through the measurement further enhances the extractable energy. As an experimentally relevant example, we analyze a waveguide-QED setup where a harmonic-oscillator battery (waveguide) is stirred and monitored by a two-level system. We characterize the performance of the protocol in terms of net extractable energy (net ergotropy) and power output.
Abstract The reduced state of a small system strongly coupled to a charger in thermal equilibrium may be athermal and used as a small battery once disconnected. By harnessing the battery-charger correlations, the battery’s extractable energy can increase above the ergotropy. We introduce a protocol that uses a quantum system as a memory that measures the charger and leaves the battery intact in its charged state. Using the information gained from the measurement, the daemonic ergotropy of the battery is extracted. Then the battery is reconnected to the charger, thermalizing and charging it. However, the memory should return to its initial standard state to close the thermodynamic cycle. Thus, on the one hand, the work cost of the cycle is the sum of the disconnecting and reconnecting battery-charger work plus the measurement and erasure work. On the other hand, the extracted energy is the daemonic ergotropy of the battery plus the ergotropy of the memory. The ratio of these quantities defines the efficiency of the cycle. The protocol is exemplified by a modified transverse spin 1/2 Ising chain, one spin functioning as the battery and the others as the charger. The memory is another auxiliary spin 1/2. We found pairs of measurement schemes from which we extract the same daemonic ergotropy from the battery, they dissipate the same amount of energy, and one leaves the memory in an active state, the other in a passive state. We study the memory’s ergotropy and the daemonic ergotropy of the battery. We find that with measurements, the efficiency can surpass that of the unmeasured protocol, given conditions on temperature, coupling, and choice of the measurement operators.
We show that a cyclic unitary process can extract work from the thermodynamic equilibrium state of an engineered quantum dissipative process. Systems in the equilibrium states of these processes serve as batteries, storing energy. The dissipative process that brings the battery to the active equilibrium state is driven by an agent that couples the battery to thermal systems. The second law of thermodynamics imposes a work cost for the process; however, no work is needed to keep the battery in that charged state. We consider simple examples of these batteries and discuss situations in which the charged state has full population inversion, in which case the extractable work is maximal, and circumstances in which the efficiency of the process is maximal.
Decoherence and dissipation in open quantum systems generally drive quantum batteries toward passive states, thereby reducing their extractable work (ergotropy). Here, we study a driven qubit quantum battery coherently coupled to an auxiliary harmonic oscillator in the presence of dephasing and dissipation. Using the differential formulation of the first law of open quantum thermodynamics, we analyze the local energy-flow dynamics during the charging process. We find that the auxiliary oscillator induces a transient negative local energy current into the qubit subsystem, corresponding to a temporary inward energy backflow. This transient energy redistribution is accompanied by an enhancement of the qubit ergotropy and a partial suppression of decoherence-induced passivation. Moreover, the parameter regime exhibiting a more pronounced negative-current interval is consistently correlated with larger ergotropy enhancement. Our results suggest that transient inward energy flow provides a useful thermodynamic signature associated with enhanced energy storage in open quantum batteries.
Harnessed nonclassical resources to enhance the performance of quantum batteries is an important goal of quantum technology. In this work, we investigate multi-emitter batteries coupled to a one-dimensional waveguide driven by a broadband squeezed-vacuum reservoir, and determine how the waveguide geometry controls the battery performance and and their thermodynamic features. We show that for a single emitter, the squeezed reservoir deposits finite energy while the state remains passive, yielding zero ergotropy. For two emitters, however, phase-sensitive reservoir correlations generate coherence and can drive the steady state into a fully nonpassive regime. For three emitters, collective thermal dynamics already supports finite ergotropy, while squeezing further increases the extractable component of the stored energy. Crucially, because the collective and phase-sensitive couplings depend on the emitter positions, geometry provides direct control over the nonclassical correlations and, consequently, over the nonpassivity of the steady state. The ergotropy can therefore be strongly modulated while the stored energy changes only weakly, and in the two-emitter configuration geometry alone can switch the battery between a passive steady state and one in which all stored energy is unitarily extractable.
Quantum batteries (QBs), acting as energy storage devices, have potential applications in future quantum science and technology. However, the QBs inevitably losses energy due to their interaction with environment. How to enhance the performance of the QBs in the open-system case remains an important challenge. Here we propose a scheme to realize the driven-dissipative QBs in atom-waveguide-QED systems and demonstrate significant improvements in both the stored energy and extractable work (ergotropy) of the QBs via feedback control. For a single-atom QB, we show that combining the measurement and coherent feedback controls enables nearly perfect stable charging under the weak coherent driving. For the QB array, the measurement-based feedback allows us to control different dynamical phases in the thermodynamic limit: (i) a continuous boundary time-crystal phase, where persistent periodic energy charge-discharge oscillations emerge despite the presence of the dissipation into the waveguide, and (ii) two stationary phases -- one reaches full charge while the other maintains only small energy storage. This work broadens the scope of driven-dissipative QBs and provides practical strategies for enhancing their performance.
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.