The reconfigurable Josephson circulator/directional amplifier

TL;DR

This paper demonstrates a reconfigurable superconducting microwave circuit that functions as both a circulator and a directional amplifier, offering low noise, reversibility, and dynamic mode switching for quantum information applications.

Contribution

It introduces a simple, three-pump Josephson circuit capable of reconfigurable non-reciprocal functions, unifying circulator and amplifier roles in a single device.

Findings

Achieved noise performance comparable to standard amplifiers.

Demonstrated reversible circulation direction.

Enabled dynamic switching between modes.

Abstract

Circulators and directional amplifiers are crucial non-reciprocal signal routing and processing components involved in microwave readout chains for a variety of applications. They are particularly important in the field of superconducting quantum information, where the devices also need to have minimal photon losses to preserve the quantum coherence of signals. Conventional commercial implementations of each device suffer from losses and are built from very different physical principles, which has led to separate strategies for the construction of their quantum-limited versions. However, as recently proposed theoretically, by establishing simultaneous pairwise conversion and/or gain processes between three modes of a Josephson-junction based superconducting microwave circuit, it is possible to endow the circuit with the functions of either a phase-preserving directional amplifier or a circulator. Here, we experimentally demonstrate these two modes of operation of the same circuit. Furthermore, in the directional amplifier mode, we show that the noise performance is comparable to standard non-directional superconducting amplifiers, while in the circulator mode, we show that the sense of circulation is fully reversible. Our device is far simpler in both modes of operation than previous proposals and implementations, requiring only three microwave pumps. It offers the advantage of flexibility, as it can dynamically switch between modes of operation as its pump conditions are changed. Moreover, by demonstrating that a single three-wave process yields non-reciprocal devices with reconfigurable functions, our work breaks the ground for the development of future, more-complex directional circuits, and has excellent prospects for on-chip integration.