# Daemonic ergotropy in continuously-monitored open quantum batteries

## TL;DR

This paper investigates how continuous environmental monitoring can enhance work extraction from quantum batteries through daemonic ergotropy, revealing bounds and measurement-dependent effects in open quantum systems.

## Contribution

It extends the concept of daemonic ergotropy to continuously-monitored open quantum systems, analyzing bounds and measurement strategies for work extraction.

## Key findings

- Daemonic ergotropy ranges between ergotropy and the system's energy.
- Maximum daemonic ergotropy achieved with pure initial states and perfect measurements.
- Measurement efficiency and initial state purity influence the ergotropy enhancement.

## Abstract

The amount of work that can be extracted from a quantum system can be increased by exploiting the information obtained from a measurement performed on a correlated ancillary system. The concept of daemonic ergotropy has been introduced to properly describe and quantify this work extraction enhancement in the quantum regime. We here explore the application of this idea in the context of continuously-monitored open quantum systems, where information is gained by measuring the environment interacting with the energy-storing quantum device. We first show that the corresponding daemonic ergotropy takes values between the ergotropy and the energy of the corresponding unconditional state. The upper bound is achieved by assuming an initial pure state and a perfectly efficient projective measurement on the environment, independently of the kind of measurement performed. On the other hand, if the measurement is inefficient or the initial state is mixed, the daemonic ergotropy is generally dependent on the measurement strategy. This scenario is investigated via a paradigmatic example of an open quantum battery: a two-level atom driven by a classical field and whose spontaneously emitted photons are continuously monitored via either homodyne, heterodyne, or photo-detection.