Abstract
We report on the design and performance of an on-chip microwave circulator with a widely (GHz) tunable operation frequency. Nonreciprocity is created with a combination of frequency conversion and delay, and requires neither permanent magnets nor microwave bias tones, allowing on-chip integration with other superconducting circuits without the need for high-bandwidth control lines. Isolation in the device exceeds 20 dB over a bandwidth of tens of MHz, and its insertion loss is small, reaching as low as 0.9 dB at select operation frequencies. Furthermore, the device is linear with respect to input power for signal powers up to hundreds of fW ( circulating photons), and the direction of circulation can be dynamically reconfigured. We demonstrate its operation at a selection of frequencies between 4 and 6 GHz.
5 More- Received 13 July 2017
DOI:https://doi.org/10.1103/PhysRevX.7.041043
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Synopsis
Quantum Circulators Simplified
Published 22 November 2017
A device that routes microwave signals could help researchers scale up quantum-computing architectures.
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Popular Summary
As experiments on superconducting qubits (the quantum equivalent of a digital bit) clear a possible path to viable quantum computing processors, further signal processing innovations are needed to preserve a high level of control over the quantum information. One bottleneck is ensuring that signals travel in only one direction, which is critical for protecting the quantum hardware from the noisy environment. Devices engineered to enforce this requirement, known as circulators, are traditionally made with permanent magnets, which makes these magnetic circulators about the size of an engagement-ring box and impractical to miniaturize. We designed and tested an alternate method for building a circulator that uses time-varying circuit parameters to simulate circulation.
Our circulator is integrated onto a chip thousands of times smaller than a magnetic circulator and built from superconducting materials. Unlike other on-chip superconducting circulators, the device has a widely tunable operation frequency and can circulate a thousand photons at a time—many more than the several-photon signals typically emitted by a single qubit. We demonstrate isolation exceeding 20 dB over a bandwidth of tens of megahertz and are able to dynamically reconfigure the circulation direction.
Circulators allow energy and information to flow out of qubits for amplification and measurement, but they strongly suppress the reverse process, where energy and information flow from the environment can damage the fragile state of the qubit. Our device offers a tunable, integrable, scalable solution that can be used in a wide variety of quantum information technologies.