Cryogenic sensor enabling broad-band and traceable power measurements

Recently, great progress has been made in the field of ultrasensitive microwave detectors, reaching even the threshold for utilization in circuit quantum electrodynamics. However, cryogenic sensors lack the compatibility with broad-band metrologically traceable power absorption measurements at ultralow powers, which restricts their range of applications. Here, we demonstrate such measurements using an ultralow-noise nanobolometer, which we extend by an additional direct-current (dc) heater input. The tracing of the absorbed power relies on comparing the response of the bolometer between radio frequency and dc-heating powers traced to the Josephson voltage and quantum Hall resistance. To illustrate this technique, we demonstrate two different methods of dc-substitution to calibrate the power that is delivered to the base temperature stage of a dilution refrigerator using our in situ power sensor. As an example, we demonstrate the ability to accurately measure the attenuation of a coaxial input line between the frequencies of 50 MHz and 7 GHz with an uncertainty down to 0.1 dB at a typical input power of -114 dBm.

Automated summary

Recently, progress has been made in ultrasensitive microwave detectors, but their range of applications is limited due to a lack of compatibility with broad-band metrologically traceable power absorption measurements. In this study, an ultralow-noise nanobolometer with an additional dc heater input was used to make such measurements. The power absorption was traced by comparing the bolometer response between radio frequency and dc-heating powers traced to the Josephson voltage and quantum Hall resistance. The ability to accurately measure the attenuation of a coaxial input line between 50 MHz and 7 GHz with an uncertainty down to 0.1 dB at a typical input power of -114 dBm was demonstrated.