Josephson-junction-based bolometer*

We recently introduced a calorimeter capable of detecting packets containing 200 8.4-GHz photons, or 1.1 zJ of energy. Now we report a record low noise equivalent power (NEP) of 50 zW/rtHz, which is reduced to 20 zW/rtHz by introducing a Josephson parametric amplifier to the readout circuitry. The lower NEP value suggests energy resolution of h×480 GHz. Sensitivity of the detector can be further increased by decreasing the heat capacity of the absorbing element. To this end, we have experimentally studied graphene as an absorber, which is promising material due to its two-dimensional structure. Our preliminary results suggest energy resolution of h×60 GHz, bringin resolution of thermal detectors close to the qubit-based detectors while maintaining superior detection bandwidth.