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

The measurement of the rapidly growing number of qubits requires a large number of customized cryogenic low-noise amplifiers (LNA).This work presents a broadband LNA designed with discrete GaAs HEMT components which operate well at ~4K temperature region. 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 wide bandwidth. Measurement results at 3.5 K ambient temperature show that the developed LNA achieved an NT of <12 Kelvin, 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. Visibility of ~0.89 is achieved when using the LNA to observe a superconducting transmon qubit.