Coherent control of a symmetry-engineered multi-qubit dark state in waveguide quantum electrodynamics

TL;DR

This paper demonstrates the creation and control of a symmetry-engineered multi-qubit dark state in waveguide quantum electrodynamics, significantly enhancing coherence times for quantum information processing.

Contribution

It introduces a method to selectively drive and control dark states in a multi-qubit waveguide system using symmetry-based drives, overcoming previous control limitations.

Findings

Dark state decay time exceeds single qubit by over two orders of magnitude

Spectroscopy reveals detailed level structure of the hybridized system

Control of dark states enables potential quantum information applications

Abstract

Quantum information is typically encoded in the state of a qubit that is decoupled from the environment. In contrast, waveguide quantum electrodynamics studies qubits coupled to a mode continuum, exposing them to a loss channel and causing quantum information to be lost before coherent operations can be performed. Here we restore coherence by realizing a dark state that exploits symmetry properties and interactions between four qubits. Dark states decouple from the waveguide and are thus a valuable resource for quantum information but also come with a challenge: they cannot be controlled by the waveguide drive. We overcome this problem by designing a drive that utilizes the symmetry properties of the collective state manifold allowing us to selectively drive both bright and dark states. The decay time of the dark state exceeds that of the waveguide-limited single qubit by more than two orders of magnitude. Spectroscopy on the second excitation manifold provides further insight into the level structure of the hybridized system. Our experiment paves the way for implementations of quantum many-body physics in waveguides and the realization of quantum information protocols using decoherence-free subspaces.