Exciting Dressed BICs Via Photon Scattering and Delayed Quantum Feedback

Giuseppe Calajó,Harold Baranger,Francesco Ciccarello,Yao-Lung Fang

doi:10.3390/proceedings2019012018

Abstract

We consider a semi-infinite waveguide with linear dispersion coupled to a qubit, in which a dressed bound state in the continuum (BIC) is known to exist. We predict that this BIC can be excited with significant probability via multi-photon scattering in the non-Markovian regime where the photon delay time (corresponding to the qubit-mirror distance) is of the order of the qubit’s decay time. A similar process excites the BIC existing in an infinite waveguide coupled to a pair of qubits, yielding stationary entanglement between them. This shows, in particular, that photon trapping via scattering can occur without band-edge effects or cavities, the essential resource being instead the delayed quantum feedback due to the mirror.

Highlights

Waveguide Quantum ElectroDynamics (QED) [1,2] is a new research area [3] investigating the coherent interaction between quantum emitters and the one-dimensional (1D) field of a waveguide.As a major motivation prompting research on this topic, waveguide-QED setups are potentially an ideal platform to carry out quantum information processing tasks, especially quantum communication [4].An intriguing effect arising from the 1D nature of the field in such setups is the formation of a dressed bound in the continuum state (BIC) [5]
The qubit behaves exactly as a bosonic mode. This is no longer true if two photons are injected, yet one can still treat the qubit as a bosonic mode of equal frequency side-coupled to the waveguide provided that a fictitious on-site photon-photon repulsion term is added to the Hamiltonian. Such repulsive interaction in particular mixes fully unbound stationary states with semi-bound ones that correspond instead to one scattering photon plus one photon bound in the BIC
We theoretically show [14] that the aforementioned dressed BIC existing in a semi-infinite waveguide coupled to one qubit can be excited via multi-photon scattering with significant probability

Summary

Introduction

Waveguide Quantum ElectroDynamics (QED) [1,2] is a new research area [3] investigating the coherent interaction between quantum emitters and the one-dimensional (1D) field of a waveguide.As a major motivation prompting research on this topic, waveguide-QED setups are potentially an ideal platform to carry out quantum information processing tasks, especially quantum communication [4].An intriguing effect arising from the 1D nature of the field in such setups is the formation of a dressed bound in the continuum state (BIC) [5]. A natural way to populate the BIC is to excite the qubit and let it decay in vacuum, a method that becomes ineffective at large time delays τ in which case the BIC’s photon component Proceedings 2019, 12, 18; doi:10.3390/proceedings2019012018 Such non-Markovian regime of non-negligible delays requires exciting the BIC’s photonic component, a task typically accomplished through photon scattering.

Results

Conclusion