Design and Characterization of a 6-mW Cryogenic SiGe IC for Superconducting Qubit Readout

In this article, a cryogenically cooled SiGe BiCMOS integrated circuit is described and used to achieve >98% readout fidelity when measuring the state of a superconducting transmon qubit coupled to a 6.5-GHz resonant cavity. The circuit employs homodyne detection and uses a novel local oscillator chopping approach to reduce the effects of LO-RF feedthrough in the presence of a high-gain LNA. At 6 mW, the integrated circuit is employed to demonstrate comparable fidelity to a standard HEMT-amplifier-based readout setup, when preceded by a Josephson parametric amplifier with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\geq \sim 18$ </tex-math></inline-formula> dB of power gain. In addition, this performance is achieved with the IC consuming less power than the commercial HEMT LNA used in the standard readout setup. To the best of the authors’ knowledge, this is the first demonstration of high-fidelity state readout of superconducting qubits without a standalone cryogenic semiconductor LNA. This demonstration represents an important step in the realization of fully integrated large-scale cryogenic qubit control systems.