On-chip Mechanical Thermometry Implemented in a Nuclear Demagnetization Cryostat

We report on microwave optomechanics measurements performed on a nuclear demagnetization cryostat. We describe a method for accessing the on-chip temperature, building on the blue-detuned parametric instability and a standard microwave setup. The capabilities and sensitivity of the experimental arrangement are demonstrated with a very weakly coupled silicon-nitride doubly clamped beam mode of about 4 MHz and a niobium on-chip cavity resonating around 6 GHz. We report on an unstable intrinsic driving force in the coupled microwave-mechanical system acting on the mechanics that appears below typically 10 mK. The origin of this phenomenon remains unknown and deserves theoretical input.

Assistant/Associate Scientist in Low Temperature Experimental Physics candidate Colloquium