Fully selective charging of a quantum battery by a purely quantum charger

Abstract

In this paper we discuss a protocol for charging a two-level quantum battery using a bipartite charger composed of two quantum harmonic oscillators. As one of its features, it allows us to fully charge the battery and is universally optimal in the regime of a single excitation added as energy input. We also make use of a selective interaction to extend the protocol for a different class of quantum states and show that, in this case, the presence of quantum coherence can be harnessed as energetic resource to charge multiple similar batteries. Among these, we also explore symmetries of the derived effective dynamics to quickly discuss how the same protocol can be adapted to the task of \textit{active state resetting}, a task which is particularly useful in the quantum computation area.

Figures (8)

• Figure 1: Full dynamics (left) connecting two quantum harmonic oscillators to a three level system. The dispersive regime gives rise to an effective interaction mixing the three different subsystems (right).
• Figure 2: The temperature range for the optimal operation of our protocol is mainly limited by the presence of initial population in the level $\ket{i}$ of the qutrit, which does not evolve in the time scale of the effective evolution and therefore does not contribute to the battery's energy gain. In these plots we present the time evolution of the internal energy in the effective qubit for the two extremal temperatures in the allowed range. As it can be seen, the SPATS scenario makes the protocol robust against temperature variations in this range, in comparison to the DTS case.
• Figure 3: Qubit's maximal internal energy for an initial inefficient SPATS left mode, as a function of its efficiency of creation. The dots represent the same quantity for the DTS initial state at the respective temperature.
• Figure 4: Qubit's internal energy in the charging protocol (upper) and ground level population in the resetting protocol (lower). Both plots are evaluated for different bare coupling strength's values and dimensionless temperature $\overline{T} = 0.1$.
• Figure 5: Final state of each qubit after interacting with the charger. The three plots show the regimes $\chi\ll 1$, $\chi = 1$, and $\chi \gg 1$, respectively. The leftmost points, as well as the drawn lines, represent the thermal population of each qubit before interaction and are fixed by the dimensionless temperature $\overline{T} = 0.1$.