Measurements of heat current and its fluctuations in superconducting quantum systems

Abstract

As the quantum systems we can control and manipulate increase in size, understanding heat dynamics becomes increasingly important. In this master’s project, we study the heat currents flowing between two out-of-equilibrium reservoirs across a superconducting quantum circuit composed of two mutually coupled, flux-tunable qubits. Electrical noise applied to the flux line of a qubit induces incoherent coupling between the modes in the single excitation manifold. Each mode is coupled to a thermal bath, realized with microwave waveguides. By coherently driving one of the modes to its first excited state, a heat current is induced. We measure heat currents on the scale of a few attoWatts, along with the fluctuations in said current. The results are compared to simulations that use full counting statistics to compute the currents and fluctuations of the process. These findings pave the way for demonstrating advantages of quantum systems over classical ones in quantum thermodynamics.