Silicon Germanium Cryogenic Low Noise Amplifiers for Quantum Computing

In this talk, we will review the state of the art in silicon germanium cryogenic amplifiers, how they are used in quantum computing, and the potential for their future use in scaled quantum computing systems. The talk will begin with a discussion of what is required to build a fault-tolerant quantum computer. Dispersive readout techniques for superconducting qubits will be presented and the hardware typically used for this function will be reviewed. Through a comparison of today’s state-of-the-art systems and what is required to enable fault-tolerant quantum computing, as well as a discussion of the limited heat-lift of cryogenic systems, it will be shown that a significant reduction in the energy consumption of the electronic systems used to interface to the quantum processor is required if fault-tolerant quantum computing is to become a reality. Furthermore, we will explain how the cryogenic low noise amplifiers used in these systems are one area in which a significant power reduction would have a large impact. Next, after a brief review of cryogenic amplifier technology (e.g., InP HEMT amplifiers), we will discuss how silicon germanium (SiGe) heterojunction bipolar transistor (HBT) technology may be used in scalable quantum readout systems. We will begin by discussing the unique properties of SiGe HBTs which make them particularly well-suited for operation at cryogenic temperatures. We will then briefly describe the recent development of discrete transistor and integrated circuit SiGe cryogenic LNAs. Next, we will discuss the potential for realizing high-performance cryogenic SiGe LNAs with power dissipations approaching 100 W, which is over an order of magnitude lower than the amplifiers employed in today’s systems. After discussing the performance implications of the low-power operation of SiGe HBTs at cryogenic temperatures, we will present a series of experimental results, including both discrete transistor and integrated circuit low noise amplifiers. The talk will conclude with a discussion of some potential ways in which SiGe technology could be further leveraged to aid in making scalable quantum computing a reality.