Tuning and Amplifying the Interactions in Superconducting Quantum Circuits with Subradiant Qubits

TL;DR

This paper introduces a tunable and amplifiable coupler for superconducting quantum circuits using N fixed-frequency qubits, enabling dynamic control and enhancement of interactions with potential applications in quantum information processing.

Contribution

It proposes a novel coupler design with a tunable interaction range proportional to N, leveraging collective qubit states to control coupling without decoherence.

Findings

Interaction range scales with N

Coupling can be switched arbitrarily within the dynamic range

Cascade of couplers can amplify weak signals

Abstract

We propose a tunable coupler consisting of N fixed-frequency qubits, which can tune and even amplify the effective interaction between two superconducting quantum circuits. The tuning range of the interaction is proportional to N, with a minimum value of zero and a maximum that can exceed the physical coupling rates between the coupler and the circuits. The effective coupling rate is determined by the collective magnetic quantum number of the qubit ensemble, which takes only discrete values and is free from collective decay and decoherence. Using single-photon pi-pulses, the coupling rate can be switched between arbitrary choices of the initial and final values within the dynamic range in a single step without going through intermediate values. A cascade of the couplers for amplifying small interactions or weak signals is also discussed. These results should not only stimulate interest in exploring the collective effects in quantum information processing, but also enable development of applications in tuning and amplifying the interactions in a general cavity-QED system.