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arXiv:2509.11050

Bound states and the collective dynamics of Distant Quantum Emitters coupled to a chiral waveguide

Meng Wu, Sun, Ge, Jing Lu, Lan Zhou

Published Sep 14, 2025• 0 citations
arXivHTMLPDF

Abstract

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.

DOI
10.48550/arxiv.2509.11050

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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 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 the problem of two-photon routing in waveguide QED ladders where a few two-level quantum emitters (QEs) are simultaneously coupled with two chiral waveguides. We analyze the routing probability in two regimes, namely, under a purely plane wave approximation (scattering case) and in the presence of photon-photon bound state formation. Within the scattering case, we examine the two-photon routing in the presence of up to five QEs, considering two possibilities separately: ideal-symmetric coupling and the critical coupling scenario. We examine the photon routing up to the two QEs for the bound state situation and compare the photon redirection efficiency with the corresponding scattering case. Our findings show the potential of utilizing chiral light-matter interactions in multi-photon and multi-emitter-based quantum networking protocols where interlinking among spatially distant nodes is required.
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.
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.
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 investigate single photon transport in two waveguides coupled to a two-level quantum emitter (QE). With the deduced analytical scattering amplitudes, we show that under condition of the chiral coupling between the QE and the photon in the two waveguides, the QE can play the role of ideal quantum router to redirect a single photon incident from one waveguide into the other waveguide with a probability of 100% in the ideal condition. The influences of cross coupling between two waveguides and dissipations on the routing are also shown.