Parametrically controlled chiral interface for superconducting quantum devices

TL;DR

This paper introduces a controllable, low-loss, and integrable chiral interface for superconducting quantum devices, enabling efficient nonreciprocal microwave routing crucial for scalable quantum computing.

Contribution

The authors design and experimentally realize a minimal, phase-controlled parametric device that achieves high directionality, offering a scalable alternative to ferrite-based circulators in quantum circuits.

Findings

Achieved around 30 dB directionality in the device.

Model predictions agree quantitatively with experimental results.

Predicted inefficiencies are at or below 1%, suitable for quantum applications.

Abstract

Nonreciprocal microwave routing plays a crucial role for measuring quantum circuits, and allows for realizing cascaded quantum systems for generating and stabilizing entanglement between non-interacting qubits. The most commonly used tools for implementing directionality are ferrite-based circulators. These devices are versatile, but suffer from excess loss, a large footprint, and fixed directionality. For utilizing nonreciprocity in scalable quantum circuits it is desirable to develop efficient integration of low-loss and in-situ controllable directional elements. Here, we report the design and experimental realization of a minimal controllable directional interface that can be directly coupled to superconducting qubits. In the presented device, nonreciprocity is realized through a combination of interference and phase-controlled parametric pumping. We have achieved a maximum directionality of around 30\,dB, and the performance of the device is predicted quantitatively from independent calibration measurements. Using the excellent agreement of model and experiment, we predict that the circuit will be useable as a chiral qubit interface with inefficiencies at the one-percent level or below. Our work offers a promising route for realizing high-fidelity signal routing and entanglement generation in all-to-all connected microwave quantum networks, and provides a path for isolator-free qubit readout schemes.