Measurement of a Superconducting Qubit with a Microwave Photon Counter

TL;DR

This paper presents a microwave photon counter for superconducting qubit measurement, achieving high fidelity and enabling scalable, quantum non-demolition measurements at millikelvin temperatures, which could improve quantum computing scalability.

Contribution

Introduces a microwave photon counter for superconducting qubit measurement, offering high fidelity and potential for scalable quantum measurement systems.

Findings

Single-shot measurement fidelity of 92%

Ability to perform repeated quantum non-demolition measurements

Access to classical measurement outcomes at millikelvin temperatures

Abstract

Fast, high-fidelity measurement is a key ingredient for quantum error correction. Conventional approaches to the measurement of superconducting qubits, involving linear amplification of a microwave probe tone followed by heterodyne detection at room temperature, do not scale well to large system sizes. Here we introduce an alternative approach to measurement based on a microwave photon counter. We demonstrate raw single-shot measurement fidelity of 92%. Moreover, we exploit the intrinsic damping of the counter to extract the energy released by the measurement process, allowing repeated high-fidelity quantum non-demolition measurements. Crucially, our scheme provides access to the classical outcome of projective quantum measurement at the millikelvin stage. In a future system, counter-based measurement could form the basis for a scalable quantum-to-classical interface.