Wideband Josephson Parametric Isolator
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.