Gain calibration of cryogenic amplification chains using normal-metal–insulator–superconductor junctions

Aalto Quantum Physics Seminar (Nanotalo). Speaker: Mr. Máté Jenei (QCD, Aalto University).

To achieve a high-efficiency readout for a low-temperature microwave circuit using cryogenic and room temperature electronics, the signal has to go through one or more amplifiers to obtain a reasonable signal-to-noise ratio. In practice, the readout line has additional losses due to different microwave components which makes the gain estimation a non-trivial task.
Here, we present a gain calibration scheme that is based on a normal-metal–insulator–superconductor junction heterostructure coupled to a superconducting microwave resonator [1]. Depending on the bias voltage applied on the heterostructure, the device can be utilized as a quantum circuit refrigerator [2]  or as an incoherent photon source [3]. For the latter case, we derive an analytic expression for the total gain that is based on only a single fitting parameter.
We present our experimental results where we reach 0.1 dB relative uncertainty of the total gain in a three-stage amplification chain.

[1] - M. Silveri et al. Phys. Rev. B 9, 96, 094524 (2017)
[2] - K. Y. Tan et al. Nat. Commun 8, 15189 (2017)
[3] - S. Masuda et al. Sci. Rep. 8, 3966 (2018)

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