Tunable Superconducting Cavity using Superconducting Quantum Interference Device Metamaterials

Samuel Kim,Jacob Alldredge,Kyle Mcelroy,Andrew Strikwerda,David Shrekenhamer

doi:10.1038/s41598-019-40891-1

Abstract

Here we consider a tunable superconducting cavity that can be used either as a tunable coupler to a qubit inside the cavity or as a tunable low noise, low temperature, RF filter. Our design consists of an array of radio-frequency superconducting quantum interference devices (rf SQUIDs) inside a superconducting cavity. This forms a tunable metamaterial structure which couples to the cavity through its magnetic plasma frequency. By tuning the resonant frequency of the metamaterial through an applied magnetic flux, one can tune the cavity mode profile. This allows us to detune the cavity initially centered at 5.593 GHz by over 200 MHz. The maximum quality factor approaches that of the empty cavity, which is 4.5 × 106. The metamaterial electromagnetic response is controlled via a low-frequency or dc magnetic flux bias, and we present a control line architecture that is capable of applying sufficient magnetic flux bias with minimal parasitic coupling. Together this design allows for an in-situ tunable cavity which enables low-temperature quantum control applications.

Highlights

Waveguide cavities provide a simple resonant system with their fundamental mode set by the speed of propagation in the cavity and the size of the cavity itself
Using these SQUID metamaterials inside a cavity, we find that the coupling between the cavity and the metamaterial occurs at the metamaterial’s magnetic plasma frequency, where the effective magnetic permeability μr = 0
A SQUID metamaterial is composed of rf SQUIDs arranged in a periodic 2D array, each of which function as a meta-atom

Summary

Introduction

Waveguide cavities provide a simple resonant system with their fundamental mode set by the speed of propagation in the cavity and the size of the cavity itself. In order to overcome these limitations and create a device useful for cavity control in cryogenic systems, we have designed an electronically tuned cavity that can be rapidly switched between states and is compatible with cryogenic temperatures This will enable novel cryogenic tunable filters as well as unique cavities that enable coupling control to and between superconducting qubits. We use a SQUID metamaterial to design and computationally model a tunable superconducting cavity that demonstrates the high level of control and the compatibility inherent within our proposed design Using these SQUID metamaterials inside a cavity, we find that the coupling between the cavity and the metamaterial occurs at the metamaterial’s magnetic plasma frequency, where the effective magnetic permeability μr = 0. This would allow the qubit to be addressed when the resonance is coupled to the qubit and isolated when it is not, allowing processing to occur during the isolation, where the qubit is insulated from outside noise improving its lifetime

Methods

Results

Conclusion