SiGe and CMOS Cryogenic Amplifiers for Superconducting Qubit Readout

The realization of a fault tolerant quantum computer is believed to require about one million physical qubits, and measuring the state of such a system is believed to require about 100,000 near quantum limited readout chains. While Josephson parametric amplifiers can be used as a first stage amplifier providing near quantum limited amplification, their gain and saturation power is limited. As such, high-gain cryogenic LNAs are typically employed at an intermediate temperature of 3K. Today, these amplifiers are usually implemented using InP HEMT technology, but to reach the scale required for fault tolerance, it is desirable to move to silicon technologies, which are mass manufacturable and, at these volumes, of considerably lower cost. In this talk, we will briefly review the state-of-the-art in quantum readout before explaining why SiGe HBT based cryo-LNAs are an excellent choice for future quantum computing systems. We will describe how the RF and noise properties of SiGe HBTs improve with cryogenic cooling and investigate their properties at very low power consumption. We will show numerous examples of SiGe LNAs that achieve state-of-the-art performance in terms of noise and power for silicon technologies. The talk will conclude with a brief discussion of the cryogenic noise properties of MOSFETs and the prospects of using these in future cryogenic LNAs.