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arXiv:2108.12951 · Physical Review A

Dissimilar collective decay and directional emission from two quantum emitters

Pablo Solano, Pablo Barberis-Blostein, Kanu Sinha

Published Feb 27, 2023• 15 citations
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Abstract

We study a system of two distant quantum emitters coupled via a one-dimensional waveguide where the electromagnetic field has a direction-dependent velocity. As a consequence, the onset of collective emission is nonsimultaneous, and, for appropriate parameters, radiation could be enhanced for one of the emitters while inhibited for the other. Interference effects enable the system to radiate in a preferential direction depending on the atomic state and the field propagation phases. We characterize such directional emission as a function of various parameters, delineating the conditions for optimal directionality.

DOI
10.1103/physreva.107.023723

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We study a system of two distant quantum emitters coupled via a one-dimensional waveguide where the electromagnetic field has a direction-dependent velocity. As a consequence, the onset of collective emission is nonsimultaneous, and, for appropriate parameters, radiation could be enhanced for one of the emitters while inhibited for the other. Interference effects enable the system to radiate in a preferential direction depending on the atomic state and the field propagation phases. We characterize such directional emission as a function of various parameters, delineating the conditions for optimal directionality.
We study a system of two distant quantum emitters coupled via a one-dimensional waveguide where the electromagnetic field has a direction-dependent velocity. As a consequence, the onset of collective emission is non-simultaneous and, for appropriate parameters, while one of the emitters exhibits superradiance the other can be subradiant. Interference effects enable the system to radiate in a preferential direction depending on the atomic state and the field propagation phases. We characterize such directional emission as a function of various parameters, delineating the conditions for optimal directionality.
We consider two two-level quantum emitters (QEs) with separations on the order of the wavelength which are chirally coupled to a one-dimensional (1D) waveguide, and the electromagnetic field of the 1D waveguide has a direction-dependent velocity, which produces two field propagation phases on the dynamics of QEs. Their spontaneous process is examined for QEs having unequal emission rates to the waveguide. It is found that radiation could be enhanced for both QEs, inhibited for both QEs, enhanced for one while inhibited for the other, completely suppressed for both QEs. In particular, the mechanism for radiation completely suppressed is the presence of a QE-photon bound state.
We study the collective decay dynamics of two or three quantum emitters coupled to a one-dimensional chiral waveguide. We find that both the asymmetry of emission intensity and the propagation phases play crucial roles in determining radiation behavior. Under suitable parameters, we show that the multiple emitters exhibit tunable radiance in the two-emitter case, such as one emitter exhibits superradiance while the other exhibits subradiance. Furthermore in the three-emitter case, the emitter can experience successive changes of radiation states. Our results highlight how chiral and anisotropic waveguide properties can be used to engineer controllable quantum light-matter interactions, with potential applications implemented in unidirectional quantum devices, and help explore more complex multibody radiation effects in waveguide quantum electrodynamics platforms.
Radiative coupling between quantum emitters leads to a range of spectacular emission phenomena. Dicke studied the foundations of collectively enhanced and suppressed decay, commonly referred to as super- and subradiance. Collective effects can further result in directionality of the emission, thus offering a complimentary implementation of chiral quantum optics. Waveguide quantum electrodynamics (QED) allows coupling between spatially separated emitters, enabling selective driving. In this work, we control the emission direction for a pair of quantum dots embedded in a bidirectional photonic crystal waveguide offering independent electrical tuning. Notably the emitters are 13 \micro m apart, which corresponds to 26 effective wavelengths, but are nevertheless radiatively coupled. The directionality arises from a dispersive dipole-dipole interaction, which shifts the energy of the collective states, so that the emitter pair effectively forms an artificial molecule. We show that the emission direction can be switched from left- to rightwards by manipulating the relative driving phase while collectively exciting the emitters. In addition, we observe directional photon statistics under continuous driving, with, for example, single photons detected on one output port, and photon pairs on the other. With pulsed excitation, both emitters are fully inverted and correlated photon pairs are observed in time-resolved intensity correlation measurements. This work demonstrates a novel implementation of chiral quantum optics using quantum dots coupled via a non-chiral waveguide, and reports key steps for scaling up as a multi-emitter waveguide QED platform.
We study the collective radiative decay of a system of two two-level emitters coupled to a one-dimensional waveguide in a regime where their separation is comparable to the coherence length of a spontaneously emitted photon. The electromagnetic field propagating in the cavity-like geometry formed by the emitters exerts a retarded backaction on the system leading to strongly non-Markovian dynamics. The collective spontaneous emission rate of the emitters exhibits an enhancement or inhibition beyond the usual Dicke superradiance and subradiance due to self-consistent coherent time-delayed feedback.
We present a theoretical investigation of collective spontaneous emission of two identical two-level atoms side-coupled to a one-dimensional semi-infinite waveguide. The presence of the waveguide boundary naturally induces a feedback interference mechanism. Our results reveal that the collective spontaneous emission rate of the two atoms can be effectively suppressed or enhanced by this interference mechanism, depending on whether the atoms are initially prepared in a symmetric or antisymmetric state. Remarkably, the maximum collective emission rate can reach twice that observed in the case of an infinite waveguide, which arises from Purcell enhancement induced by the waveguide boundary. Further analysis of the two-atom collective dynamics reveals that, under appropriate conditions, an atom-photon bound state can be formed, leading to the confinement of emitted photons within the atom-atom or atom-boundary interspace. These results offer potential applications in quantum information processing based on waveguide quantum electrodynamics.