Pulsed HEMT LNA Operation for Qubit Readout

Large-scale qubit readout in quantum computing systems requires highly sensitive amplification with minimal power consumption to reduce the thermal load and preserve qubit integrity. We propose a pulse-operated cryogenic low-noise amplifier (LNA) scheme that minimizes the influence of the LNA on qubit operation and reduces power consumption by duty cycling. A modified commercially available cryogenic hybrid LNA based on InP high-electron mobility transistors (HEMTs) has been characterized to demonstrate the feasibility of pulsed operation for qubit readout. The transient noise and gain performance of the LNA were obtained through a cryogenic time domain noise measurement setup with 5-ns time resolution and a measured noise standard deviation (SD) below 0.3 K. The time-domain noise and gain performance of the LNA in response to a square gate voltage waveform were investigated. Through an analysis of the LNA’s recovery limitations, we developed a fast recovery bias strategy leading to the optimization of the gate voltage waveform using a genetic algorithm (GA). This resulted in a strong enhancement of transient noise and gain performance with a recovery time of 35 ns. The drain current transients were measured to calculate the average power consumption of the pulse-operated LNA, which confirmed a reduction in average power consumption proportional to the duty cycle. This work contributes to the development of high-performance and low-power amplifier solutions critical for large-scale qubit readout applications.