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Advanced Quantum Technologies

Single‐Excitation Scattering With Waveguide QED in A Cavity‐Trapping‐Two‐Atoms System

Qing‐Lin Liu, Xiaoyu Huang, Zhipeng Cheng, Rong‐Bo Du, Xin‐Qi He, Jun Jin, Hong‐Yu Liu, Rong‐Can Yang, Ying Ming

Published Jun 1, 2026• 0 citations
Publisher

Abstract

ABSTRACT We propose a scheme for the single‐photon routing in a hybrid system composed of the cavity‐trapping‐two‐atoms system (CTAS) coupled to two one‐dimensional coupled‐resonator waveguides. By employing the discrete‐coordinate scattering method, exact analytical expressions for the single‐photon scattering amplitudes at the four ports are derived. The results demonstrate that the single‐photon routing characteristics depend not only on the coupling positions, coupling strengths, and local coupling phases between the CTAS and the waveguides, but also critically on the eigenstate structure of the CTAS. Further analysis reveals a clear correspondence between the single‐photon scattering spectrum and the eigenstates of the CTAS, which allows for the classification of the eigenstates involved in cross‐waveguide transport as bright and dark states. By tuning the local coupling phases, coherent enhancement of a specific bright state can be achieved, enabling deterministic single‐photon directional routing. Our work provides a theoretical reference for studies of single‐photon routing in cavity quantum electrodynamics and superconducting circuit platforms.

DOI
10.1002/qute.70351

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ABSTRACT We propose a scheme for the single‐photon routing in a hybrid system composed of the cavity‐trapping‐two‐atoms system (CTAS) coupled to two one‐dimensional coupled‐resonator waveguides. By employing the discrete‐coordinate scattering method, exact analytical expressions for the single‐photon scattering amplitudes at the four ports are derived. The results demonstrate that the single‐photon routing characteristics depend not only on the coupling positions, coupling strengths, and local coupling phases between the CTAS and the waveguides, but also critically on the eigenstate structure of the CTAS. Further analysis reveals a clear correspondence between the single‐photon scattering spectrum and the eigenstates of the CTAS, which allows for the classification of the eigenstates involved in cross‐waveguide transport as bright and dark states. By tuning the local coupling phases, coherent enhancement of a specific bright state can be achieved, enabling deterministic single‐photon directional routing. Our work provides a theoretical reference for studies of single‐photon routing in cavity quantum electrodynamics and superconducting circuit platforms.
In this paper, we propose a single-photon routing scheme using a hybrid system, where a two-level giant atom is coupled to a pair of one-dimensional coupled-resonator waveguides. Using the discrete-coordinate scattering approach, exact expressions of the four scattering coefficients are obtained, and the single-photon routing properties are studied. We find that the single-photon routing properties are closely related to the size of the giant atom, the coupling strength between the giant atom and waveguides, and the phase difference between two coupled channels of the atom-upper (lower) waveguide. Without considering the effect of phases of the atom-waveguide coupling coefficients, the probability for a single-photon routing from one waveguide to the other does not exceed 5050%50. However, by properly selecting coupling points between the giant atom and two waveguides, and the phase difference between two atom-upper (lower) waveguide coupling coefficients, a single photon can be transferred from the input port to an arbitrarily selected output port deterministically, i.e., with 100100%100 probability. It is also found that chiral and nonreciprocal single-photon scattering can be realized in our model by properly adjusting the phase difference between two atom-upper (lower) waveguide coupled channels. Our paper offers a promising route towards achieving tunable single-photon routing and constructing optical scalable quantum networks.
Abstract We present a theoretical study of controlled single-photon routing in a cavity-quantum electrodynamics system coupled to dual waveguides, where each cavity embedding with a two-level atom mediates photon transport between two channels. The proposed system achieves enhanced routing performance through tailored phase-dependent cavity–waveguide couplings that generate optimized quantum interference patterns. Using a real-space formalism, we derive analytical expressions for single-photon scattering amplitudes and identify optimal conditions for maximum routing efficiency. Our analysis shows that targeted routing with near-unity efficiency can be realized by precisely manipulating both the accumulated phase and differential phase shift, while the atom–cavity coupling strength enables frequency-selective tunability. Furthermore, we demonstrate engineered nonreciprocal transmission and chiral scattering, enabling deterministic control over photonic propagation direction. This phase-tunable protocol establishes a scalable platform for quantum network implementation and enables novel functionalities in photonic quantum information processing.
The dynamic control of single-photon scattering in a pair of one-dimensional waveguides mediated by a time-modulated atom–cavity system is investigated. Two cases, where the waveguides are coupled symmetrically or asymmetrically to the atom–cavity system, are discussed in detail. The results show that such time-modulated atom–cavity configuration can behave as a dynamical tunable directional single-photon router. The photons with different frequencies can dynamically be routed from the incident waveguide into any ports of the other with a 100% probability via adjusting the modulated amplitude or phases of the time-modulated atom–cavity coupling strengths, associate with the help of the asymmetrical waveguide–cavity couplings. Furthermore, the influence of dissipation on the routing capability is investigated. It is shown that the present single-photon router is robust against the dissipative process of the system, especially the atomic dissipation. These results are expected to be applicable in quantum information processing and design quantum devices with dynamical modulation.
Abstract We investigate the single-photon transport properties in a hybrid waveguide quantum electrodynamics system, in which a one-dimensional waveguide is simultaneously coupled to a cavity and a driven Λ-type three-level atom. The cavity and the atom are also coupled to each other. We show that when the waveguide is coupled to the cavity and the atom at the same point, double electromagnetically induced transparency (EIT) can be observed from the system. The physical mechanism of the double EIT effect has been given by setting up the eigenstate structure for the whole system. When the waveguide is coupled to the cavity and the atom at different points, we demonstrate that the single-photon transmission spectra can be effectively controlled by adjusting the relative separation between the cavity and the atom. Moreover, this non-zero relative separation can lead to the occurrence of the controllable nonreciprocal scattering effect. These results have potential applications in realization of photonic coherent control.
We theoretically investigate coherent controlling single photon transport in one-dimensional waveguide coupled to a giant atom interacting with a resonator. The giant atom is considered as a Λ-type system. One transition of the atom couples to the waveguide and the other one is driven by the resonator. Single photon scattering amplitudes are calculated for three kinds of coupling schematics, respectively. Both the analytical and numerical results show that single photon scattering properties can be manipulated by adjusting the size of the giant atom, the coupling strengths of the waveguide-resonator and resonator-giant atom. Specifically, the transmission spectra exhibit two Rabi-splitting dips and the locations of the dips are strongly dependent on the size of the giant atom (GA). It also shows that the resonant single photon can be tuned from being transmitted to being reflected by controlling the coupling strength. Our results may find applications in designing quantum devices based on giant atom at single-photon level.
Abstract We investigate single-photon quantum routing composed of double two-level atoms coupled to two infinite waveguides. By introducing local coupling phases at atom-waveguide connecting points, we engineer asymmetric atom-waveguide interactions, which enables the directional control of photon propagation for achieving high-efficiency quantum routing. Using the real-space approach, we derived exact expressions of the single-photon scattering amplitudes, allowing for a comprehensive analysis of the routing dynamics. For both identical and non-identical atomic configurations, we systematically explored the conditions for achieving perfect photon transfer. Our results demonstrate that complete photon transfer can be realized by precisely tuning the coupling phases, the accumulated phase and atomic frequencies. This work provides a theoretical foundation for developing high-efficiency quantum routers with potential applications in quantum networks and photonic quantum information processing.