Leveraging Collective Effects for Thermometry in Waveguide Quantum Electrodynamics

We report a proof-of-principle experiment for a new method of temperature measurements in waveguide quantum electrodynamics experiments, allowing one to measure separately the temperature of global and local baths. The method takes advantage of collective states of two transmons located in the center of a waveguide. The Hilbert space of such a system forms two separate subspaces (bright and dark) that are coupled differently to external noise sources. Measuring transmission through the waveguide allows one to extract separately the temperatures of the baths responsible for global and local excitations in the system. Such a system would allow for building a new type of primary temperature sensor capable of addressing both local and global baths.