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

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.

Exact Markovian and non-Markovian time dynamics in waveguide QED: collective interactions, bound states in continuum, superradiance and subradiance

“…For example, for N = 3, we have observed several non-Markovian Fano minima (in addition to 2 that are observed in the Markovian limit [35]) in our own explorations. [56] observes similar effects for a twoqubit system. We believe that this is an interesting phenomenon to study as a future work.…”

2022 Roadmap on integrated quantum photonics

“…Enhanced Bragg reflection off a chain of identical atoms trapped in an optical lattice in a waveguide was demonstrated in [158]. An ensemble of emitters interfacing with a waveguide, as shown in figure 22, exhibits a myriad of exotic phenomena such as single-photon super-and sub-radiance [159,160], nonreciprocal photon transport, and asymmetrical Fano lineshapes. When the lattice periodicity equals an integer multiple of the wavelength, the cooperative emission from the atomic array retains its Lorentzian profile with a linearly scaling decay rate, as has been demonstrated in [159,161].…”

“…An ensemble of emitters interfacing with a waveguide, as shown in figure 22, exhibits a myriad of exotic phenomena such as single-photon super-and sub-radiance [159,160], nonreciprocal photon transport, and asymmetrical Fano lineshapes. When the lattice periodicity equals an integer multiple of the wavelength, the cooperative emission from the atomic array retains its Lorentzian profile with a linearly scaling decay rate, as has been demonstrated in [159,161]. By stimulating interaction between photons, a multi-spin cluster can serve as an optical switch or nearly any possible quantum gate.…”

Manipulating single-photon transport in a waveguide-QED structure containing two giant atoms

“…Thus quantum devices with high efficiency, including quantum routers [4,10,[23][24][25][26], single-photon transistors [9,27] and quantum frequency converters [28][29][30][31][32][33], can be realized in the wQED structures. In particular, when two or more atoms coupled to a 1D continuum, the interactions mediated by the guided modes as well as the interferences between photons re-emitted by different atoms, can enable a number of interesting effects, such as asymmetric Fano lineshapes [34][35][36][37][38], electromagnetically induced transparency (EIT) without control field [39][40][41], waveguide-mediated entanglement between distant atoms [42][43][44][45], generation of photonic band gap [46,47], cavity QED with atomic mirrors [48,49], creating and engineering superradiant and subradiant states [50][51][52][53], and so on.…”

“…Then, based on these general expressions, we further analyze two important phenomena, asymmetric Fano lineshape and EIT without control field, which can be observed from the scattering spectra. These phenomena also exist in the wQED system containing multiple small atoms [34][35][36][37][38][39][40][41], but their counter part in giant-atom systems will give rise to some different features due to additional interference effects and diverse configurations. Specifically, we find that the appearance of Fano interferences is strongly influenced by both the phase delay between coupling points and the topologies of system.…”