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Journal of Physics B Atomic Molecular and Optical Physics

Directional single-photon frequency conversion in a chiral-giant-atom waveguide-QED system

Haozhen Li, Ran Zeng, Miao Hu, Xuefang Zhou, Mengmeng Xu, Xiuwen Xia

Published Jan 21, 2026• 1 citation
Publisher

Abstract

Abstract Single-photon frequency conversion in the system composed of a Λ -type three-level giant atom chiral couples to a one-dimensional waveguide is investigated. Two configurations, i.e. one of the atomic transitions couples to the waveguide at two separated points while the other one either directly or indirectly couples to the waveguide at a single point, are considered. The scattering amplitudes for representing the frequency conversion in the two kinds of coupling schematics are obtained analytically with the real-space approach. The results show that perfect nonreciprocal transmission with preserving frequency and ideal directional frequency conversion can be realized due to the time-reversal symmetry broken induced by the chiral coupling as well as the self-interference comes from the giant atom. In particular, in the indirect coupling configuration, the scattering spectra exhibit two directional frequency conversion windows due to the atom-cavity coupling, which enables the present system suitable for the simultaneous manipulation of incident photons with different frequencies. These results may have potential applications in various quantum information processing and quantum network engineering.

DOI
10.1088/1361-6455/ae3b3c

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Abstract Single-photon frequency conversion in the system composed of a Λ -type three-level giant atom chiral couples to a one-dimensional waveguide is investigated. Two configurations, i.e. one of the atomic transitions couples to the waveguide at two separated points while the other one either directly or indirectly couples to the waveguide at a single point, are considered. The scattering amplitudes for representing the frequency conversion in the two kinds of coupling schematics are obtained analytically with the real-space approach. The results show that perfect nonreciprocal transmission with preserving frequency and ideal directional frequency conversion can be realized due to the time-reversal symmetry broken induced by the chiral coupling as well as the self-interference comes from the giant atom. In particular, in the indirect coupling configuration, the scattering spectra exhibit two directional frequency conversion windows due to the atom-cavity coupling, which enables the present system suitable for the simultaneous manipulation of incident photons with different frequencies. These results may have potential applications in various quantum information processing and quantum network engineering.
-type atom coupled to a T-shaped waveguide. By controlling local coupling phases to engineer quantum interference, perfect directional frequency conversion is achieved without an engineered chiral waveguide structure. The multi-path interference of the giant atom, combined with local phase tuning, enables flexible control over photon transmission direction and frequency, supporting multiple directional conversion channels. In the Markovian limit, the cavity-mediated structure realizes two fully efficient directional channels, while under non-Markovian conditions, retardation effects open several distinct frequency conversion windows. This phase-controlled, multi-frequency directional architecture provides a versatile platform for frequency-multiplexed quantum routing and networking.
We study single-photon scattering spectra of a giant atom chirally coupled to a one-dimensional waveguide at multiple connection points, and examine chirality-induced effects in the scattering spectra. We show that the transmission spectra typically possess an anti-Lorentzian lineshape with a nonzero minimum, but by engineering the chirality of the multipoint coupling, the transmission spectrum of an incident photon can undergo a transition from complete transmission to total reflection at multiple frequency ``windows,'' where the width of the anti-Lorentzian lineshape for each of the window can be flexibly tuned at a fixed frequency detuning. Moreover, we show that a perfect nonreciprocal photon scattering can be achieved due to the interplay between internal atomic spontaneous emission and the chirally external decay to the waveguide, in contrast to that induced by the non-Markovian retardation effect. We also consider the non-Markovian retardation effect on the scattering spectra, which allows for a photonic band gap even with only two chiral coupling points. The giant-atom-waveguide system with chiral coupling is a promising candidate for realizing single-photon routers with multiple channels.
In this paper, we employ two two-level atoms and a $\mathrm{\ensuremath{\Lambda}}$-type atom to connect two one-dimensional semi-infinite coupled resonator waveguides, respectively. The first configuration is a chiral setup, where incident photons undergo an elastic scattering process. We investigate the influence on the single-photon transfer rate of spatial coupling points between the small or giant atom and the waveguides. Our numerical simulations demonstrate that additional coupling points in the giant atom system will modify the transmission rule observed in the small atom system due to their unique interference effects. The second configuration is a nonreciprocal setup, where the conduction direction depends entirely on the initial state of the $\mathrm{\ensuremath{\Lambda}}$-type atom. The incident photon undergoes an inelastic scattering process accompanied by frequency conversion.
We study chiral and nonreciprocal single-photon scattering in a chiral-giant-molecule waveguide-QED system. Here, the giant molecule consists of two coupled giant atoms, which interact with two linear waveguides, forming a four-port quantum device. We obtain the exact analytical expressions of the four scattering amplitudes using a real-space method. Under the Markovian limit, we find that the single-photon scattering behavior is determined by the coupling strength between the giant atoms and the waveguides, the coupling strength between the two giant atoms, and the nondipole effect caused by the phase accumulation of photons traveling between the coupling points. It is also found that chiral and nonreciprocal single-photon scattering can be realized by introducing the chiral coupling to break the symmetry in the coupling configuration between the giant molecule and the waveguides. In addition, an ideal chiral emitter-waveguide coupling enables a directional single-photon routing. In the non-Markovian regime, the scattering spectra are characterized by more abundant structures with multiple peaks and dips. In particular, we demonstrate that the non-Markovian retarded effect can induce the nonreciprocal single-photon scattering. Our results have potential applications in the design of optical quantum devices involving giant atoms, which can provide an efficient platform for studying chiral quantum optics.
We study the single-photon scattering in a one-dimensional (1D) waveguide coupled to one transition of a VVV-type giant atom (GA), whose other transition is coherently driven by an classical field. The inelastic scattering of single photons by the GA realizes the single-photon frequency conversion. By applying the Lippmann-Schwinger equation, the scattering coefficients for single photons incident from different directions are obtained, which present different scattering spectra in the Markovian and the non-Markovian regimes. The conversion contrast characterizing the nonreciprocity is also analyzed in both regimes. It is found that the probability of the frequency up- or down-conversion vanishes as long as the emission from either transition pathways for single photons is suppressed, but it is enhanced and even reach unity by introducing the nonreciprocity. It is the quantum self-interference induced by the scale of this two-legged GA and the phase difference between the GA-waveguide couplings that tune the probability of the frequency up- or down-conversion.
In this paper, we begin with a model of a $\mathrm{\ensuremath{\Lambda}}$-type atom whose both transitions are chirally coupled to a wave guide and then extend the model to its giant-atom version. We investigate the single-photon scatterings of the giant-atom model in both the Markovian and the non-Markovian regimes. It is shown that the chiral atom-wave-guide couplings enable nonreciprocal, reflectionless, and efficient frequency conversion, while the giant-atom structure introduces intriguing interference effects to the scattering behaviors, such as ultranarrow scattering windows. The chiral giant-atom model exhibits quite different scattering spectra in the two regimes and, in particular, demonstrates non-Markovicity-induced nonreciprocity under specific conditions. These phenomena can be understood from the effective detuning and decay rate of the giant-atom model. We believe that our results have potential applications in integrated photonics and quantum network engineering.