# Heat and work along individual trajectories of a quantum bit

## TL;DR

This paper experimentally tracks individual quantum trajectories of a driven qubit, distinguishing heat and work, and verifies the first law of thermodynamics in an open quantum system using advanced measurement techniques.

## Contribution

It introduces a method to experimentally differentiate heat and work along quantum trajectories and verifies thermodynamic principles at the quantum level.

## Key findings

- Successful experimental tracking of quantum trajectories
- Verification of the first law of thermodynamics for a qubit
- Consistency with master equation and two-measurement schemes

## Abstract

We use a near quantum limited detector to experimentally track individual quantum state trajectories of a driven qubit formed by the hybridization of a waveguide cavity and a transmon circuit. For each measured quantum coherent trajectory, we separately identify energy changes of the qubit as heat and work, and verify the first law of thermodynamics for an open quantum system. We further establish the consistency of these results by comparison with the master equation approach and the two-projective-measurement scheme, both for open and closed dynamics, with the help of a quantum feedback loop that compensates for the exchanged heat and effectively isolates the qubit.