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Optics Express

Tunable directional collective emission of two or three quantum emitters in a chiral waveguide

Xiaoyu Yao, Fuli Li

Published Jun 19, 2025• 2 citations
Publisher

Abstract

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.

DOI
10.1364/oe.567080

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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 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.
In our work, we theoretically study the dynamics of a single excitation in a one-dimensional array of two-level systems, which are chirally coupled through a single mode waveguide. The chirality is achieved owing to a strong optical spin-locking effect, which in an ideal case gives perfect unidirectional excitation transport. We obtain a simple analytical solution for a single excitation dynamics in the Markovian limit, which directly shows the tolerance of the system with respect to the fluctuations of emitters position. We also show that the Dicke state, which is well known to be superradiant, has twice lower emission rate in the case of unidirectional quantum interaction. Our model is supported and verified with the numerical computations of quantum emitters coupled via surface plasmon modes in a metallic nanowire. The obtained results are based on a very general model and can be applied to any chirally coupled system that gives a new outlook on quantum transport in chiral nanophotonics.
When multiple quantum emitters couple to a common electromagnetic environment, interference in their collective radiative dynamics gives rise to superradiance and subradiance. In regimes where coherent interactions and collective dissipation compete, the microscopic many-body dynamics and quantum correlations among the emitters that underlie superradiance and subradiance are theoretically challenging and remain experimentally elusive, even though collective emission has been observed in many physical systems. Here, we realize a superconducting qubit array coupled to a common microwave waveguide that mediates collective dissipation, with simultaneous access to coherent interactions and microscopic measurements of many-body dynamics. Engineered qubit-waveguide couplings with tunable amplitude and phase enable control of collective interference and the resulting super- and subradiant states. Leveraging site-resolved control and readout, we directly observe the microscopic decay dynamics of multi-qubit states across different excitation manifolds and track the evolution of populations and tunable quantum correlations. We reveal collective decay in regimes beyond the ideal Dicke model, where strong qubit-qubit interactions stabilize superradiance and subradiance against local dephasing and reshape decay pathways through spatially and spectrally structured many-body eigenstates. Our results establish a flexible platform for exploring collective phenomena in many-body quantum optics and driven-dissipative approaches to robust quantum information processing.
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.
Photon emission is the hallmark of light-matter interaction and the foundation of photonic quantum science, enabling advanced sources for quantum communication and computing. Although single-emitter radiation can be tailored by the photonic environment, the introduction of multiple emitters extends this picture. A fundamental challenge, however, is that the radiative dipole-dipole coupling rapidly decays with spatial separation, typically within a fraction of the optical wavelength. We realize distant dipole-dipole radiative coupling with pairs of solid-state optical quantum emitters embedded in a nanophotonic waveguide. We dynamically probe the collective response and identify both super- and subradiant emission as well as means to control the dynamics by proper excitation techniques. Our work constitutes a foundational step toward multiemitter applications for scalable quantum-information processing.