Multi-Path Interferometric Josephson Directional Amplifier for Qubit Readout

TL;DR

This paper presents a quantum-limited, directional Josephson amplifier for qubit readout, utilizing interferometric coupling of nondegenerate three-wave-mixing amplifiers to achieve nonreciprocity and reflection suppression.

Contribution

The authors develop a novel interferometric scheme with phase-gradient control to realize a compact, on-chip, quantum-limited directional amplifier for quantum measurements.

Findings

Achieved directional amplification with high gain and low noise.

Demonstrated good agreement between experimental results and theoretical models.

Proposed an improved design to eliminate bulky off-chip isolation components.

Abstract

We realize and characterize a quantum-limited, directional Josephson amplifier suitable for qubit readout. The device consists of two nondegenerate, three-wave-mixing amplifiers that are coupled together in an interferometric scheme, embedded in a printed circuit board. Nonreciprocity is generated by applying a phase gradient between the same-frequency pumps feeding the device, which plays the role of the magnetic field in a Faraday medium. Directional amplification and reflection-gain elimination are induced via wave interference between multiple paths in the system. We measure and discuss the main figures of merit of the device and show that the experimental results are in good agreement with theory. An improved version of this directional amplifier is expected to eliminate the need for bulky, off-chip isolation stages that generally separate quantum systems and preamplifiers in high-fidelity, quantum-nondemolition measurement setups.