Microwave attenuators for use with quantum devices below 100 mK

TL;DR

This paper presents the development and characterization of microwave attenuators operating below 100 mK, designed to reduce thermal noise in superconducting quantum devices, with detailed thermal modeling and noise temperature measurements.

Contribution

The paper introduces thin-film microwave attenuators with specific heat sink design for ultra-low temperature operation, providing quantitative noise temperature data and thermal behavior analysis.

Findings

Minimum noise temperature T_n ≤ 53 mK at no power

T_n increases with dissipated power following P_d^(1/5.4)

Attenuators effectively reduce thermal noise in quantum devices

Abstract

To reduce the level of thermally generated electrical noise transmitted to superconducting quantum devices operating at 20 mK, we have developed thin-film microwave power attenuators operating from 1 to 10 GHz. The 20 dB and 30 dB attenuators are built on a quartz substrate and use 75 nm thick films of nichrome for dissipative components and 0.001 mm thick silver films as hot electron heat sinks. The noise temperature of the attenuators was quantified by connecting the output to a 3D cavity containing a transmon qubit and extracting the dephasing rate of the qubit as a function of temperature and dissipated power P_d in the attenuator. The minimum noise temperature T_n of the output from the 20 dB attenuator was T_n less than and equal to 53 mK for no additional applied power and T_n about 120 mK when dissipating 30 nW. In the limit of large dissipated power (P_d > 1 nW) we find T_n proportional to P_d^(1/5.4), consistent with detailed thermal modeling of heat flow in the attenuators.