Sub-mW Cryogenic InP HEMT LNA for Qubit Readout

The cryogenic indium phosphide (InP) high-electron-mobility transistor (HEMT) low-noise amplifier (LNA) is used for the readout amplification of qubits at 4 K where cooling capabilities are limited implying that the dc power of the active circuits is an essential design constraint. In this article, the RF and noise performance of the InP HEMT under ultralow-power (ULP) operation at 4 K has been characterized. The small-signal and noise parameter model of the InP HEMT was extracted down to
$1~\mu \text{W}$
. The tradeoff between noise performance and dc power consumption was analyzed in terms of the drain current and drain voltage. A 4–6 GHz hybrid cryogenic HEMT LNA designed for qubit readout and optimized for lowest noise below 1 mW dc power consumption was fabricated. The measured performance of the LNA at 4 K attained 23.1 dB average gain and 2.0 K average noise temperature at 200
$\mu \text{W}$
dc power.