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Photonic and Phononic Properties of Engineered Nanostructures

Ultrafast single-photon spontaneous emission from an array of quantum-emitters along a photonic waveguide

Zihao Chen, Jung‐Tsung Shen, Yao Zhou

Published Feb 21, 2018• 5 citations
Publisher

Abstract

In a waveguide-QED system, under certain condition, the spontaneous emission rate of an atom cloud with a single excitation can be enhanced. Single-photon superradiance refers to the case when the enhancement attains its maximum. We show that an atom cloud exhibiting single-photon superradiance can be described by an effective two-level system. We also adopt a real space numerical approach to validate the understanding of single-photon superradiance using such an effective mapping picture. We further numerically investigate the spontaneous emission of superradiant state and dark state.

DOI
10.1117/12.2289379

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In a waveguide-QED system, under certain condition, the spontaneous emission rate of an atom cloud with a single excitation can be enhanced. Single-photon superradiance refers to the case when the enhancement attains its maximum. We show that an atom cloud exhibiting single-photon superradiance can be described by an effective two-level system. We also adopt a real space numerical approach to validate the understanding of single-photon superradiance using such an effective mapping picture. We further numerically investigate the spontaneous emission of superradiant state and dark state.
A recent experiment reveals the linear scaling property of the superradiant emission rate for a trapped atom cloud that is excited by weak and short light pulses. We adopt a real-space approach to numerically demonstrate that such a linear scaling law can be interpreted as single-photon superradiance, in both the time domain and the frequency domain. The dependence of the single-photon superradiant emission rate on the distance between atoms is investigated. We further study the single-photon superradiance for artificial atoms that have deviations in transition frequencies and decay rates.
Atom coherence in the cooperative interaction between the atoms and a single photon creates ultrafast spontaneous emission and ultrastrong intensity peaks, namely single-photon superradiance, which has attracted considerable research interest in the recent years. As the investigation for such a single-photon superradiance usually involves only quantum emitters, in this paper we present the cooperative atom-photon interaction in a system including whispering gallery mode resonators, which are one of the most essential components in nanophotonic devices. Here we both analytically and computationally show that the separated atoms on a resonator can obtain cooperative interaction, manifesting superradiant coupling strength, which results in the ultrafast spontaneous emission and ultrastrong intensity peaks. The conditions of such single-photon superradiance are called whispering gallery mode superradiance conditions. Furthermore, the atoms are proved to have cooperative interaction on a cascade of resonators by a renormalization approach.
We study the collective emission of a disordered array of N excited two-level atoms into a one-dimensional photonic waveguide. In the perfectly ordered case, where atoms are spaced by exact integer multiples of the wavelength, the system exhibits the characteristic superradiant burst with a peak emission rate scaling as N 2 . Using large-scale semiclassical simulations, we find that this key signature of superradiance remains asymptotically robust under strong spatial and spectral disorder, but also exhibits subtle finite-size scaling toward this limit. To explain our observations, we provide an analytical variational estimate for the maximal decay rate, which tightly bounds the numerical results and reveals how disorder shapes the collective decay. Specifically, we find that even in the presence of strong disorder, the spins tend to self-organize spontaneously according to their locations, which overall optimizes constructive interference effects and explains the emergence of mirror-asymmetric correlations in superradiant decay. These findings resolve important open questions regarding the existence and nature of superradiance in strongly disordered arrays and offer valuable insights for understanding collective quantum optical phenomena in realistic systems.
Recent work has shown that collective single photon emission from an ensemble of resonate two-level atoms, i.e., single photon superradiance, is a rich field of study. The present Letter addresses the flip side of superradiance, i.e., subradiance. Single photon subradiant states are potentially stable against collective spontaneous emission and can have ultrafast readout. In particular it is shown how many atom collective effects provide a new way to control spontaneous emission by preparing and switching between subradiant and superradiant states.
As a manifestation of cooperative interactions between a single photon and a cluster of atoms, single-photon superradiance has attracted considerable attention recently but has been studied insofar as that only quantum emitters are involved in the superradiance process. Here we expand the scope of investigation to study single-photon superradiance in a waveguide-quantum-electrodynamical system containing whispering-gallery-mode (WGM) resonators which are essential for many nanophotonic devices. It is shown analytically and numerically that single-photon superradiance can also occur when WGM resonators are present. The criteria for the emergence of the superradiant emission peak and the enhanced atom-light coupling strength are derived. Finally, the general case of a cascade of WGM resonators is investigated by a renormalization approach. Single-photon frequency comb generation is demonstrated via a frequency-modulated superradiant effective atom in chiral waveguide-quantum-electrodynamical systems with WGM resonators.
Quantum emitters coupled to a waveguide are a paradigm of quantum optics, whose essential properties are described by waveguide quantum electrodynamics (QED). We study the possibility of observing the typical features of the conventional waveguide QED scenario in a system where the role of the waveguide is played by a one-dimensional subwavelength atomic array. For the role of emitters, we propose to use antisymmetric states of atomic dimers---a pair of closely spaced atoms---as effective two-level systems, which significantly reduces the effect of free-space spontaneous emission. We solve the dynamics of the system both when the dimer frequency lies inside and when it lies outside the band of modes of the array. Along with well-known phenomena of collective emission into the guided modes and waveguide-mediated long-range dimer-dimer interactions, we uncover significant non-Markovian corrections which arise from both the finiteness of the array and through retardation effects.