High-fidelity qubit measurement with a microwave photon counter

TL;DR

This paper introduces a fast, high-fidelity, scalable qubit measurement method using cavity ring-up and Josephson photomultiplier detection, enabling efficient quantum nondemolition readout suitable for scalable quantum computing.

Contribution

It proposes a novel measurement scheme combining cavity ring-up and JPM detection, eliminating the need for room-temperature electronics and enhancing scalability for superconducting qubits.

Findings

Achieves over 95% measurement contrast

Measurement time of 140 ns

Potential for multi-qubit channel scaling

Abstract

High-fidelity, efficient quantum nondemolition readout of quantum bits is integral to the goal of quantum computation. As superconducting circuits approach the requirements of scalable, universal fault tolerance, qubit readout must also meet the demand of simplicity to scale with growing system size. Here we propose a fast, high-fidelity, scalable measurement scheme based on the state-selective ring-up of a cavity followed by photodetection with the recently introduced Josephson photomultiplier (JPM), a current-biased Josephson junction. This scheme maps qubit state information to the binary digital output of the JPM, circumventing the need for room-temperature heterodyne detection and offering the possibility of a cryogenic interface to superconducting digital control circuitry. Numerics show that measurement contrast in excess of 95% is achievable in a measurement time of 140 ns. We discuss perspectives to scale this scheme to enable readout of multiple qubit channels with a single JPM.