A 3.5~7.5 GHz GaAs HEMT Cryogenic Low-NoiseAmplifier Achieving 5 Kelvin Noise Temperature for Qubits Measurement

The measurement of the fast-increasing number of qubits necessitates the use of a large number of specialized cryogenic low-noise amplifiers (LNAs).). This work presents a broadband LNA designed with discrete GaAs HEMT components which operate well at ~3.6 K temperature. The dual-frequency optimum noise matching network and output matching elements of the first stage were employed to optimize the equivalent noise temperature (NT) and the input return loss in a wideband. Measurement results at 3.6 K ambient temperature show that the LNA achieved an equivalent NT of <12 K, and a gain of >30 dB in the 3.5 GHz to 7.5 GHz band with a minimum of 5 Kelvin at ~6.5 GHz. The best visibility of ~0.891 is achieved when using the LNA to observe a superconducting transmon qubit without using a JPA.