A fast and large bandwidth superconducting variable coupler

TL;DR

This paper introduces a superconducting microwave variable coupler with broad bandwidth, fast switching, high on-off ratio, and dissipation-free operation, suitable for quantum communication and superconducting qubit integration.

Contribution

The authors present a novel chip-based superconducting coupler with over 1.5 GHz bandwidth, rapid 10 ns tuning, and high on-off ratio, advancing quantum-compatible microwave routing technology.

Findings

Achieved over 40 dB on-off ratio in the coupler.

Demonstrated tunability over 4-8 GHz frequency range.

Coupler can switch coupling state in approximately 10 nanoseconds.

Abstract

Variable microwave-frequency couplers are highly useful components in classical communication systems, and likely will play an important role in quantum communication applications. Conventional semiconductor-based microwave couplers have been used with superconducting quantum circuits, enabling for example the in situ measurements of multiple devices via a common readout chain. However, the semiconducting elements are lossy, and furthermore dissipate energy when switched, making them unsuitable for cryogenic applications requiring rapid, repeated switching. Superconducting Josephson junction-based couplers can be designed for dissipation-free operation with fast switching and are easily integrated with superconducting quantum circuits. These enable on-chip, quantum-coherent routing of microwave photons, providing an appealing alternative to semiconductor switches. Here, we present and characterize a chip-based broadband microwave variable coupler, tunable over 4-8 GHz with over 1.5 GHz instantaneous bandwidth, based on the superconducting quantum interference device (SQUID) with two parallel Josephson junctions. The coupler is dissipation-free, features large on-off ratios in excess of 40 dB, and the coupling can be changed in about 10 ns. The simple design presented here can be readily integrated with superconducting qubit circuits, and can be easily generalized to realize a four- or more port device.