Amplifying microwave pulses with a single qubit engine fueled by quantum measurements

TL;DR

This paper demonstrates microwave signal amplification using a quantum engine powered by measurement backaction on a superconducting qubit, validating the work output through direct and indirect methods and analyzing stability and robustness.

Contribution

It introduces a quantum engine fueled by measurement backaction that amplifies microwave signals without a hot thermal source, a novel experimental demonstration.

Findings

Successful amplification of microwave signals using a measurement-driven quantum engine

Validation of work output measurement methods showing good agreement

Analysis of engine stability and robustness to decoherence and system drifts

Abstract

Recent progress in manipulating individual quantum systems enables the exploration of engines exploiting non-classical resources. One of the most appealing is the energy provided by the inherent backaction of quantum measurements. While a handful of experiments have investigated the inner dynamics of engines fueled by measurement backaction, powering a task by such an engine is missing. Here we demonstrate the amplification of microwave signals by an engine fueled by repeated quantum measurements of a superconducting transmon qubit. Using feedback, the engine acts as a quantum Maxwell demon operating without a hot thermal source. Measuring the gain of this amplification constitutes a direct probing of the work output of the engine, in contrast with inferring the work by measuring the qubit state along its evolution. Observing a good agreement between both work estimation methods, our experiment validates the accuracy of the indirect method. We characterize the long-term stability of the engine as well as its robustness to transmon decoherence, loss and drifts. Our experiment exemplifies the use of energy brought by quantum measurement backaction.