Comment on "High-Power Collective Charging of a Solid-State Quantum Battery"

TL;DR

This paper critically analyzes a previous claim of quantum advantage in a quantum battery, demonstrating that the observed enhancement is a classical effect, not due to quantum entanglement or collective quantum phenomena.

Contribution

It clarifies that the claimed quantum advantage in the Dicke quantum battery is actually a classical effect caused by stronger cavity fields, challenging prior interpretations.

Findings

The stablished ffect is classical, not quantum.

The laimed nhancement arises from classical cavity field effects.

The laim of quantum advantage is misleading and not supported by quantum entanglement evidence.

Abstract

In the Letter [Physical Review Letters 120, 117702 (2018)], Ferraro \emph{et al.} claimed a quantum advantage in the Dicke quantum battery (QB), whereby $N$ two-level systems (TLS) are coupled to a common photonic mode of a cavity. They argued that compared with the so-called Rabi QB, the Dicke QB exhibits a $\sqrt{N}$ quantum enhancement in the charging power because of the entanglement created by the common photonic mode. In this Comment, however, we demonstrate that the apparent $\sqrt{N}$ enhancement actually comes from the stronger cavity electric (or magnetic) field under the setup discussed in [Physical Review Letters 120, 117702 (2018)]. This is a trivial classical effect, and there is no true "quantum advantage" in the charging power of the Dicke QB. While somewhat similar questions regarding the origin of the claimed "quantum advantage" have been raised before, here we would like to make it clear that the $\sqrt{N}$ enhancement in [Physical Review Letters 120, 117702 (2018)] is purely a classical effect, not attributable to quantum entanglement or collective phenomena. Therefore, we believe that using the term "quantum battery" in this context may be inappropriate and misleading.