Wideband Josephson Parametric Isolator

The cryogenic hardware needed to build a superconducting qubit based quantum computer requires a variety of microwave components including microwave couplers, filters, amplifiers, and circulators/isolators. Traditionally, these are implemented via discrete components inserted in to the signal path. As qubit counts climb over the 100+ mark, the integration of these peripheral components, in an effort to reduce overall footprint, thermal load, and added noise in the overall system, is a key challenge to scaling. Ferrite-based microwave isolators are one of the physically largest devices that continue to remain as discrete components. They are generally employed in the readout chain to protect qubits and resonators from broadband noise and unwanted signals emanating from downstream components such as amplifiers. Here we present an alternative two-port isolating integrated circuit derived from the DC Superconducting Quantum Interference Device (DC-SQUID). The non-reciprocal transmission is achieved using the three-wave microwave mixing properties of a flux-modulated DC-SQUID. We show experimentally that, when multiple DC-SQUIDs are embedded in a multi-pole admittance inverting filter structure, RF 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.