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arXiv:2511.10243

Tunable single-photon frequency converter in a waveguide with a giant V-type atom

Hongzheng Wu, Ge Sun, Jing Lu, Lan Zhou

quant-phSubmitted Nov 13, 2025• Announced Nov 14, 2025• 0 citations
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Abstract

We study the single-photon scattering in a one-dimensional (1D) waveguide coupled to one transition of a $V$-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.

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Communications in Theoretical Physics•Jul 5, 2024•6 citations
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.
We propose a scheme to achieve efficient frequency conversion for a single photon propagating in a 1D conventional waveguide by exploiting the quantum interference induced by the scale of a V-type giant atom (GA) characterized by the distance between the two coupling points as well as single-photon transition pathways originated from the coupling between the GA and the resonator. The presence of photons in the resonator triggers the frequency conversion of photons. The scattering spectra and the conversion contrast are studied in both the Markovian and the non-Markovian regimes. The disappearance of frequency conversion is rooted in the complete suppression of the emission from the excited state to either of lower states in the n+1n+1n+1 subspace where nnn is the photon number of the resonator, and the non-Markovicity-induced nonreciprocity is found under specific conditions. Altering the photon number nnn induces the non-reciprocal transmission of single photons in the waveguide, hence, enhance the conversion probability.
The single photon scattering properties in a waveguide coupling to a giant atom with a three-level system are investigated theoretically. One of the transitions of the giant atom couples to the waveguide at two points while the other one is driven by a classical field. Using the analytical expressions of the single photon scattering amplitudes, the conditions for realizing perfect single photon nonreciprocal scattering are discussed in both Markovian regime and non-Markovian regime. In the Markovian regime, the perfect non-reciprocity can be realized by adjusting the external classical field, the energy dissipation of the giant atom, the phase difference between the two coupling strengths and the accumulated phase resulting from the photon propagating between the two coupling points. In the non-Markovian regime, the non-reciprocal scattering phenomenon becomes more abundant due to the time delay. However, the analytical results show that the perfect non-reciprocity can still be achieved. When the incident photon is resonant with the giant atom, the nonreciprocity can be switched by controlling the classical field. For the non-resonant single photon, one can adjust the Rabi frequency of the classical field to obtain the perfect non-reciprocal single photon transmission. Our work provides a manner to realize a frequency tunable single photon diode.
Abstract The single-photon frequency conversion in a one-dimensional waveguide coupled to a giant three-level atom is investigated. The analytical expressions of the single-photon scattering spectra are derived via the real-space Hamiltonian. Numerical results show that high-efficiency frequency conversion of single photons can be achieved by controlling the atom-waveguide coupling due to the phase-dependent interference effect of the multiple point couplings of the giant atom, and the conversion efficiency can ideally reach unity. The conversion spectra in both the Markovian and non-Markovian regimes show that multiple staggered peaks and dips emerge due to the non-Markovian retardation effect, in contrast to a single peak and dip in the Markovian regime. The influence of dissipation on the fidelity of frequency conversion is also displayed, and it shows that the fidelity is not sensitive to dissipation.
In this work, we utilize a two-level atom and a $\mathrm{\ensuremath{\Lambda}}$-type atom to link two identical waveguides, subsequently extending the model to a giant-atom configuration. Our analytical solutions and numerical simulations demonstrate that this setup can achieve single-photon isolation and nonreciprocal frequency conversion by tuning the atom-waveguide coupling strengths gi{g}_{i}gi​, respectively. We also examine single-photon scattering in the giant-atom model within both the Markovian and non-Markovian regimes. The results reveal that ultranarrow scattering windows are induced by the phases ${\ensuremath{\phi}}_{1}$ and ${\ensuremath{\phi}}_{2}$ under specific conditions, making them well suited for precise frequency conversion and sensing. Additionally, in the non-Markovian regime, the spectra exhibit irregular polygonal shapes, offering enhanced opportunities for exploring nonreciprocal frequency conversion in the off-resonant regime. Our work provides an alternative perspective on achieving optical nonreciprocity at the single-photon level in atom-waveguide systems.
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.
Abstract A waveguide-QED with giant atoms, which is capable of accessing various limits of a small one, provides a new paradigm to study photon scatterings. Thus, how to achieve nonreciprocal photon transmissions via such a giant atom setup is highly desirable. In this study, the nonreciprocal single-photon scattering characteristics of a double-driven Λ-type three-level giant atom, where one of the transition couples to a 1D waveguide at two separate points, and the other is driven by two coherent driving fields, are investigated. It is found that a frequency-tunable single-photon diode with an ideal contrast ratio can be achieved by properly manipulating the local coupling phases between the giant atom and the waveguide, the accumulation phase between the two waveguide coupling points, the Rabi frequencies and phase difference of the two driven fields. Compared to the previous single driving schemes, on the one hand, the presence of the second driving field can provide more tunable parameters to manipulate the nonreciprocal single-photon scattering behavior. On the other hand, here perfect nonreciprocal transmission for photons with arbitrary frequencies is achievable by tuning the driving phases while the two driving fields keep on turning, which provides an alternative way to control the nonreciprocal single-photon scattering. Furthermore, the results reveal that both the location and width of each optimal nonreciprocal transmission window is also sensitive to the driving detuning, and a single-photon diode with wide or narrow bandwidth can be realized based on demand. These results may be beneficial for designing nonreciprocal single-photon devices based on a double-driven giant atom setup.