Indefinite Causal Order in Quantum Batteries

TL;DR

This paper explores how indefinite causal order in quantum processes can enhance quantum battery charging, enabling higher energy storage and more efficient protocols than classical causal order, revealing novel quantum advantages.

Contribution

It introduces the application of indefinite causal order to quantum batteries, demonstrating improved charging protocols and potential cost reductions in measurement-based protections.

Findings

Superposed unitary chargers fully charge batteries despite local Hamiltonians.

Indefinite causal order chargers outperform classical ones in non-unitary protocols.

Less powerful chargers can sometimes charge batteries to higher energies.

Abstract

Operations performing on quantum batteries are extended to scenarios where we no longer force the existence of definite causal order of occurrence between distinct processes. In contrast to standard theories, the so called indefinite causal order is found to have the capability of accomplishing tasks that are not possible without it. Specifically, we show how this novel class of resource comes into play in quantum batteries by first, combining two static unitary chargers into a coherently superposed one to fully charge an empty battery even if in the presence of battery's local Hamiltonian. Then we demonstrate for a non-unitary charging protocol, the indefinite causal order version charger yields a charged battery with higher energy over its classical counterpart under any conditions. We also have a finding that runs counter to our intuition which, roughly speaking, has the implication that a relatively less powerful charger guarantees a charged battery with higher energy. Finally, to reduce the cost imposed by a measurement-based protection scheme, indefinite causal order shows its potential to fulfill this goal.