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.
Highlights
Cooperative effects play an important role in the behavior and time evolution of quantum systems
In order to compute the BICs emerging in our model, we need to solve Eqs. (13) and (14), with the propagator matrix being given by Eq (11); once we solve this problem, finding the admissible energies E of the BICs and the corresponding excitation profiles a, the associated photon wavefunction is given by Eq (16)
We analyzed the emergence of BICs in a regular array of quantum emitters in a waveguide
Summary
Cooperative effects play an important role in the behavior and time evolution of quantum systems. Such effects compete with the dephasing induced by the dipoledipole interactions In this scenario, among the most interesting phenomena there are certainly super- and subradiance, by which the spontaneous emission of radiation in a transition between two atomic levels leads to coherent emission by an atomic ensemble, enhancing [1–3] or reducing [4] the decay rate. While superradiance has been extensively studied since Dicke’s seminal proposal [1], subradiance in large cold atom clouds has been observed only rather recently [7, 8] These phenomena take place at light wavelengths that are typically much larger than interatomic distances [9, 10], a number of interesting quantum resonance effects appear at shorter wavelengths, comparable to the distance among atoms.
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