# Multiple Fano interferences due to waveguide-mediated phase-coupling between atoms

## TL;DR

This paper investigates quantum interference effects in waveguide-coupled atomic chains, revealing multiple Fano minima, phase-dependent phenomena, and broadband reflection features in photon transport.

## Contribution

It provides an analytical framework for understanding waveguide-mediated phase-coupling effects on multi-atom systems and their impact on reflection spectra.

## Key findings

- Multiple Fano minima in reflection spectra due to interference.
- Phase tuning can suppress certain spectral features.
- Broadband high reflectivity with plateau-shaped spectra.

## Abstract

We examine quantum interference effects due to absorption and emission from multiple atoms coupled to a waveguide and highlight the modifications they entail in regards to single-photon transport properties. A prominent upshot of these interference phenomena is the resonant suppression of the reflection amplitude, which leads to the observation of multiple Fano minima in the reflection spectrum. Such minima determine the points at which transparency is induced in the system. By taking recourse to the real-space Hamiltonian framework, we calculate analytically the reflectivity and transmissivity for a one-dimensional waveguide that evanescently couples to a chain of equally spaced quantum emitters. The inter-emitter spacing relative to the wavelength of the propagating photon, leading to a waveguide-mediated "phase-coupling" between the atoms, is found to fundamentally affect the existence of Fano minima. For a chain of $N$ atoms, the number of minima can be at most $N-1$. However, suitable choices of the phase can suppress the discernibility of the full range of roots in the reflection spectrum. A principal observation for the case of multiple emitters is the emergence of super-Gaussian characteristics close to zero-detuning and consequently, a plateau-shaped broadband spectrum in the region of high reflectivity. For a large chain size, the plateau gets transformed into a flat-topped quasi-rectangular profile in the frequency domain.