Wideband Josephson Parametric Isolator

TL;DR

This paper introduces an integrated, superconducting circuit isolator based on flux-modulated DC-SQUIDs, offering a compact, broadband alternative to traditional ferrite isolators for quantum computing readout chains.

Contribution

The work presents a novel integrated microwave isolator using flux-modulated DC-SQUIDs, achieving over 15 dB directionality across 600 MHz bandwidth, reducing size and complexity in quantum hardware.

Findings

Achieved >15 dB isolation over 600 MHz bandwidth.

Demonstrated flux-pumped DC-SQUIDs enable non-reciprocal microwave transmission.

Integrated design reduces footprint compared to ferrite-based isolators.

Abstract

The cryogenic hardware required to build a superconducting qubit based quantum computer demands a variety of microwave components. These elements include microwave couplers, filters, amplifiers, and circulators/isolators. Traditionally implemented as discrete components, integration of this peripheral hardware, in an effort to reduce overall footprint, thermal load, and added noise, is a key challenge to scaling modern quantum processors with qubit counts climbing over the 100+ mark. Ferrite--based microwave isolators, generally employed in the readout chain to decouple qubits and resonators from readout electronics, persist as one of the volumetrically largest devices still utilized as discrete components. Here we present an alternative two--port isolating integrated circuit derived from the DC Superconducting Quantum Interference Device (DC-SQUID). Non-reciprocal transmission is achieved using the three-wave microwave mixing properties of a flux-modulated DC--SQUID. We show that when multiple DC-SQUIDs are embedded in a multi--pole admittance inverting filter structure, the three-wave mixing derived from the flux pumping of the DC-SQUIDs can provide directional microwave power flow. For a three--pole filter device, we experimentally demonstrate a directionality greater than 15 dB over a 600 MHz bandwidth.