Theory of multi-qubit superradiance in a waveguide in the presence of finite delay times

TL;DR

This paper investigates the quantum dynamics of multiple qubits in a waveguide, revealing how finite delay times and feedback effects influence superradiance, decay rates, and quantum correlations, with implications for entanglement and quantum information.

Contribution

It provides a numerically exact analysis of multi-qubit superradiance in waveguides considering finite delay times, highlighting non-Markovian effects and the generation of long-term quantum correlations.

Findings

Delay times significantly affect collective decay rates.

Finite feedback influences quantum correlations and entanglement.

Long-term quantum correlations can be engineered through initial states and delays.

Abstract

We study the quantum dynamics of multiple two-level atoms (qubits) in a waveguide quantum electrodynamics system, with a focus on modified superradiance effects between two or four atoms with finite delay times. Using a numerically exact matrix product approach, we explore both Markovian and non-Markovian regimes, and highlight the significant influence of time-delayed feedback effects and the clear breakdown of assuming instantaneous coupling dynamics. We first show a system composed of two spatially separated qubits, prepared in a doubly excited state (both fully excited), and provide a comprehensive study of how delayed feedback influences the collective system decay rates, as well as the quantum correlations between waveguide photons, atoms, and between atom and photons. The system is then extended to include two additional qubits located next to the initial ones (four qubits in total), and we demonstrate, by manipulating the initial excitations and the time-delay effects, how long-term quantum correlations and light-matter entangled states can be established.