Quantum Information: Thermodynamics out of Equilibrium

The precision of nanoscale heat engines is limited in the classical regime by the thermodynamic uncertainty relation (TUR). This relation defines a trade-off between power output, fluctuations, and entropic cost. Quantum effects may allow for a precision enhancement, potentially violating the TUR bound. However, experimentally demonstrating this enhancement is monumentally challenging, particularly due to the difficulty in measuring tiny heat currents and their fluctuations. Here, we provide the first measurement of heat fluctuations in a superconducting quantum thermal machine coupled to a thermal reservoir. The system is based on a superconducting artificial molecule—made of two transmon qubits— coupled in a symmetry-selective manner to a microwave waveguide. We coherently drive the transition between the ground state and one excited state. Next, we couple the two upper levels through a dephasing channel, acting as an infinite temperature bath. Finally, we measure the statistical moments of the instantaneous output power emitted into the waveguide, acting as a cold bath, and thereby evaluate the TUR. Furthermore, theoretical predictions suggest that this device could potentially violate the TUR, paving the way for experimental evidence of a quantum advantage in thermodynamics.