Stationary excitation waves and multimerization in arrays of quantum emitters

TL;DR

This paper investigates bound states and multimer formation in arrays of quantum emitters coupled to a waveguide, revealing sinusoidal excitation profiles and the emergence of emitter subsets with vanishing fields.

Contribution

It characterizes bound states in the continuum for arbitrary emitter numbers and introduces the concept of multimers with specific spatial arrangements.

Findings

Bound states exhibit sinusoidal excitation profiles.

Multimers are formed with emitters separated by two lattice spacings.

Evanescent fields underpin the observed phenomena.

Abstract

We explore the features of an equally-spaced array of two-level quantum emitters, that can be either natural atoms (or molecules) or artificial atoms, coupled to a field with a single continuous degree of freedom (such as an electromagnetic mode propagating in a waveguide). We investigate the existence and characteristics of bound states, in which a single excitation is shared among the emitters and the field. We focus on bound states in the continuum, occurring in correspondence of excitation energies in which a single excited emitter would decay. We characterize such bound states for an arbitrary number of emitters, and obtain two main results, both ascribable to the presence of evanescent fields. First, the excitation profile of the emitter states is a sinusoidal wave. Second, we discuss the emergence of multimers, consisting in subsets of emitters separated by two lattice spacings in which the electromagnetic field is approximately vanishing.