Slowing down light in a qubit metamaterial

TL;DR

This paper demonstrates the ability to slow down microwave electromagnetic waves in a superconducting qubit metamaterial, advancing quantum memory and information processing technologies.

Contribution

It introduces two methods for controlling wave speed in a superconducting qubit system, achieving significant reduction in group velocity.

Findings

Reduced group velocity by a factor of 1500

Controlled wave speed using microwave tones or qubit detuning

Demonstrated flexible dispersion engineering in superconducting circuits

Abstract

The rapid progress in quantum information processing leads to a rising demand for devices to control the propagation of electromagnetic wave pulses and to ultimately realize a universal and efficient quantum memory. While in recent years significant progress has been made to realize slow light and quantum memories with atoms at optical frequencies, superconducting circuits in the microwave domain still lack such devices. Here, we demonstrate slowing down electromagnetic waves in a superconducting metamaterial composed of eight qubits coupled to a common waveguide, forming a waveguide quantum electrodynamics system. We analyze two complementary approaches, one relying on dressed states of the Autler-Townes splitting, and the other based on a tailored dispersion profile using the qubits tunability. Our time-resolved experiments show reduced group velocities of down to a factor of about 1500 smaller than in vacuum. Depending on the method used, the speed of light can be controlled with an additional microwave tone or an effective qubit detuning. Our findings demonstrate high flexibility of superconducting circuits to realize custom band structures and open the door to microwave dispersion engineering in the quantum regime.