Heat measurement of quantum interference

TL;DR

This paper demonstrates the measurement of quantum coherence effects in heat transfer between a driven flux qubit and a thermal bath, revealing interference patterns and resonance phenomena, advancing understanding in quantum thermodynamics.

Contribution

It presents the first experimental observation of coherence effects in heat transport in a quantum system, supported by a Floquet theoretical model.

Findings

Detection of interference patterns in heat current due to coherence

Resonance peaks at fractional frequencies of the resonator

Parity selection rule at the qubit symmetry point

Abstract

Coherence is a key property of quantum systems, and it plays a central role in the operation and performance of quantum heat engines and refrigerators. Despite its importance for the fundamental understanding in quantum thermodynamics and its technological implications, coherence effects in heat transport have not been observed previously. Here, we measure quantum features in the heat transfer between a qubit and a thermal bath. The system is formed of a driven flux qubit galvanically coupled to a $\lambda/4$ coplanar-waveguide resonator that is coupled to a heat reservoir. This thermal bath is a normal-metal mesoscopic resistor, whose temperature can be measured and controlled. We detect interference patterns in the heat current due to driving-induced coherence. In particular, resonance peaks in the heat transferred to the bath are found at driving frequencies which are integer fractions of the resonator frequency. A selection rule on the even/odd parity of the peaks holds at the qubit symmetry point. We present a theoretical model based on Floquet theory that captures the experimental results. The studied system provides a platform for studying the role of coherence in quantum thermodynamics. Our work opens the possibility to demonstrate a true quantum thermal machine where heat is measured directly.