Quantum process inference for a single qubit Maxwell's demon

TL;DR

This paper uses quantum process matrices to unify the description of thermodynamic processes in quantum systems, demonstrating optimal feedback protocols in a superconducting circuit Maxwell's demon to improve work extraction and efficiency.

Contribution

It introduces quantum process matrices as a unified framework for quantum thermodynamics and experimentally applies this to optimize feedback in a quantum Maxwell's demon.

Findings

Quantum process matrices effectively describe thermodynamic processes.

Optimal feedback protocols enhance work extraction and efficiency.

Experimental validation in superconducting circuits confirms theoretical predictions.

Abstract

While quantum measurement theories are built around density matrices and observables, the laws of thermodynamics are based on processes such as are used in heat engines and refrigerators. The study of quantum thermodynamics fuses these two distinct paradigms. In this article, we highlight the usage of quantum process matrices as a unified language for describing thermodynamic processes in the quantum regime. We experimentally demonstrate this in the context of a quantum Maxwell's demon, where two major quantities are commonly investigated; the average work extraction $\langle W \rangle$ and the efficacy $\gamma$ which measures how efficiently the feedback operation uses the obtained information. Using the tool of quantum process matrices, we develop the optimal feedback protocols for these two quantities and experimentally investigate them in a superconducting circuit QED setup.