Fig. 2: Microwave cavity and photon detector used in this work.
From: Detection of single-mode thermal microwave photons using an underdamped Josephson junction
a The cavity, critically coupled to the SPD through antenna port 2, while port 1 is weakly coupled and used for characterization purposes. At the center of the cavity, a sketch of the 14 GHz mode shape is shown. b Room-temperature response of the cavity, showing resonant modes starting from the fundamental mode at 8.81 GHz. A comparison with resonances at 17 mK is provided in Fig. 4. (c) Circuit diagram with optical images of the detector connected to the cavity antenna and mounted in the sample holder. SEM image of the Josephson junction with artificial colors: pink - bottom Al electrode, blue - top Al electrode, violet - overlapping areas. The feeding dc lines are also shown, indicating the bias current Ib and measured voltage U. d Picture of the coldest plate of the dilution refrigerator, showing the sample holder within the cryoperm screen and the copper cavity. A SQUID thermometer is mounted on top, with a heating resistor installed below.
