Microwave bolometer with low noise equivalent power

Aalto Quantum Physics Seminar (Nanotalo). Speaker: Mr. Roope Kokkoniemi (QCD, Aalto University, Finland).

We recently introduced a calorimeter capable of detecting packets containing 200 8.4-GHz photons, or 1.1 zJ of energy [1]. The detector consists of a series of capacitively grounded Josephson junctions strongly coupled to an absorber. The resulting LC-oscillators resonance frequency is strongly modulated by the absorbed energy due to the exponential dependence of the Josephson junctions critical current on the electron temperature. Lately, we have measured a similar microwave detector in a bolometer mode, i.e., we measure power in a continuous microwave signal. We observed a record low noise equivalent power (NEP) of 50 zW/rtHZ. Furthermore, we incorporated a Josephson parametric amplifier to our readout circuitry. This improves the NEP by over a factor of two, down to 20 zW/rtHZ. We will also discuss ongoing experiments with the calorimetric detectors.

[1] J. Govenius, R.E. Lake, K.Y. Tan, and M. Möttönen  Phys. Rev. Lett. 117 (2016) 030802.