Real-time millikelvin thermometry in a semiconductor-qubit architecture

We report local time-resolved thermometry in a silicon-nanowire quantum dot device designed to host a linear array of spin qubits. Using two alternative measurement schemes based on rf reflectometry, we are able to probe either local electron or bosonic bath temperatures with microsecond time scale resolution and a noise-equivalent temperature of 30.2em0exmK/√Hz. Following the application of short microwave pulses, causing local periodic heating, time-dependent thermometry can track the dynamics of thermal excitation and relaxation, revealing clearly different characteristic time scales. This work opens important prospects to investigate the out-of-equilibrium thermal properties of semiconductor quantum electronic devices operating at very low temperature. In particular, it may provide a powerful handle to understand heating effects recently observed in semiconductor spin-qubit systems.