Methods for characterization and minimization of microwave background in cryogenic environment

Minimizing microwave background of cryogenic environment is crucial for quantum devices where single microwave photon energy is sufficient to disturb the measured system. Microwave photons with sufficient energy originate from the warmer parts of the cryostat, for example from parts at liquid helium temperature (4.2 K), which can be about three orders of magnitude higher than the sample temperature. Reduction of the microwave background is possible with careful design of both shielding and filtering of the sample holder. Additionally, on-chip filtering of the actual quantum device can improve the device performance significantly.