Efficient and Low-Backaction Quantum Measurement Using a Chip-Scale Detector

TL;DR

This paper introduces a chip-scale superconducting switch that enables fast, high-fidelity quantum measurements of superconducting qubits with low backaction, replacing bulky non-reciprocal components and advancing scalable quantum computing.

Contribution

It demonstrates a scalable, integrated superconducting device that combines amplification and isolation for qubit measurement, eliminating the need for non-reciprocal magnetic components.

Findings

Achieved 70% measurement efficiency.

Measured a transmon qubit with high fidelity and speed.

Replaced bulky circulators with a chip-scale superconducting switch.

Abstract

Superconducting qubits are a leading platform for scalable quantum computing and quantum error correction. One feature of this platform is the ability to perform projective measurements orders of magnitude more quickly than qubit decoherence times. Such measurements are enabled by the use of quantum-limited parametric amplifiers in conjunction with ferrite circulators - magnetic devices which provide isolation from noise and decoherence due to amplifier backaction. Because these non-reciprocal elements have limited performance and are not easily integrated on-chip, it has been a longstanding goal to replace them with a scalable alternative. Here, we demonstrate a solution to this problem by using a superconducting switch to control the coupling between a qubit and amplifier. Doing so, we measure a transmon qubit using a single, chip-scale device to provide both parametric amplification and isolation from the bulk of amplifier backaction. This measurement is also fast, high fidelity, and has 70% efficiency, comparable to the best that has been reported in any superconducting qubit measurement. As such, this work constitutes a high-quality platform for the scalable measurement of superconducting qubits.