The Pound-Drever-Hall Method for Superconducting-Qubit Readout

TL;DR

This paper introduces an ultrastable superconducting qubit readout method using the multi-tone Pound-Drever-Hall technique, demonstrating high phase stability, insensitivity to phase drift, and potential for enhanced signal-to-noise ratio in quantum computing.

Contribution

The work adapts the PDH technique for superconducting qubit readout, showing improved stability and signal quality over traditional methods.

Findings

Phase stability of 0.73° over 2 hours

Single-shot readout capability despite phase errors

Potential 14 dB signal enhancement

Abstract

Scaling quantum computers to large sizes requires the implementation of many parallel qubit readouts. Here we present an ultrastable superconducting-qubit readout method using the multi-tone self-phase-referenced Pound-Drever-Hall (PDH) technique, originally developed for use with optical cavities. In this work, we benchmark PDH readout of a single transmon qubit, using room-temperature heterodyne detection of all tones to reconstruct the PDH signal. We demonstrate that PDH qubit readout is insensitive to microwave phase drift, displaying $0.73^\circ$ phase stability over 2 hours, and capable of single-shot readout in the presence of phase errors exceeding the phase shift induced by the qubit state. We show that the PDH sideband tones do not cause unwanted measurement-induced state transitions for a transmon qubit, leading to a potential signal enhancement of at least $14$~dB over traditional heterodyne readout.