Scalable two- and four-qubit parity measurement with a threshold photon counter

TL;DR

This paper introduces a scalable method for measuring two- and four-qubit parity using photon counting and dispersive coupling, suitable for quantum error correction in various quantum computing platforms.

Contribution

It proposes a low-overhead, robust parity measurement scheme based on photon counting and dispersive coupling, applicable to superconducting circuits and other modalities.

Findings

High measurement contrast close to ideal parity measurement

Robustness to experimental imperfections demonstrated

Suitable for quantum error correction protocols

Abstract

Parity measurement is a central tool to many quantum information processing tasks. In this Letter, we propose a method to directly measure two- and four-qubit parity with low overhead in hard- and software, while remaining robust to experimental imperfections. Our scheme relies on dispersive qubit-cavity coupling and photon counting that is sensitive only to intensity; both ingredients are widely realized in many different quantum computing modalities. For a leading technology in quantum computing, superconducting integrated circuits, we analyze the measurement contrast and the back action of the scheme and show that this measurement comes close enough to an ideal parity measurement to be applicable to quantum error correction.