Nonreciprocal single-photon scattering in a one-dimensional waveguide coupled to a giant two-level atom assisted with a time-modulated single-mode cavity is investigated. The analytic expressions of the single-photon scattering amplitudes are derived by using an effective Floquet Hamiltonian in real space. The scattering characteristics are discussed detail in both the Markovian and the non-Markovian regimes, and the corresponding conditions for achieving perfect nonreciprocal single-photon transmission are obtained. In the Markovian regime, a frequency-tunable single-photon diode with an ideal transmission contrast ratio can be realized by adjusting the frequency of the cavity mode, the local coupling phase difference, and the accumulated phase between the two coupling points. Furthermore, the influence of the intrinsic energy dissipations on the photon transport is discussed in detail. It is found that the dissipations of the cavity and the giant atom affect discriminatively the nonreciprocal single-photon scattering process. In the non-Markovian regime, the influence of the non-Markovian retarded effect induced by the time delay on the nonreciprocal single-photon scattering is discussed in detail. The results reveal that, although the retarded effect leads to a complex nonreciprocal scattering spectrum, dynamic tunable perfect nonreciprocal transmission with more abundant physical phenomena suitable for photons with different frequencies within a larger range can also be achieved. Such a nonreciprocal single-photon device can be used as an elementary unit for various quantum information processing and may have potential applications in quantum network engineering.
Nonreciprocal single-photon scattering in a one-dimensional waveguide coupled to a giant two-level atom assisted with a time-modulated single-mode cavity is investigated. The analytic expressions of the single-photon scattering amplitudes are derived by using an effective Floquet Hamiltonian in real space. The scattering characteristics are discussed detail in both the Markovian and the non-Markovian regimes, and the corresponding conditions for achieving perfect nonreciprocal single-photon transmission are obtained. In the Markovian regime, a frequency-tunable single-photon diode with an ideal transmission contrast ratio can be realized by adjusting the frequency of the cavity mode, the local coupling phase difference, and the accumulated phase between the two coupling points. Furthermore, the influence of the intrinsic energy dissipations on the photon transport is discussed in detail. It is found that the dissipations of the cavity and the giant atom affect discriminatively the nonreciprocal single-photon scattering process. In the non-Markovian regime, the influence of the non-Markovian retarded effect induced by the time delay on the nonreciprocal single-photon scattering is discussed in detail. The results reveal that, although the retarded effect leads to a complex nonreciprocal scattering spectrum, dynamic tunable perfect nonreciprocal transmission with more abundant physical phenomena suitable for photons with different frequencies within a larger range can also be achieved. Such a nonreciprocal single-photon device can be used as an elementary unit for various quantum information processing and may have potential applications in quantum network engineering.
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 phase-controlled single-photon transport properties of a giant atom coupled to a one-dimensional waveguide are investigated. The coupling between the giant atom and the waveguide is modeled as a multi-point interaction. The coupling strengths between the giant atom and the waveguide are represented as complex numbers with associated phases. Analytical expressions for the scattering amplitudes are obtained using the real-space Hamiltonian method. The results show that the characteristics of the scattering spectra, including the positions of peaks (or dips) and the full width at half maximum, can be tuned by adjusting the phase difference between the coupling strengths. Further calculations reveal that the scattering spectra can be either super-broadened or sub-broadened. The conditions for achieving perfect nonreciprocal single-photon transport in the Markovian regime are also discussed. Moreover, we demonstrate the control of single-photon transport through phase differences in the non-Markovian regime. Our results may find applications in the design of quantum devices operating at the single-photon level, based on waveguide quantum electrodynamics.
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.
Abstract We explore the scattering and nonreciprocal transmission of single photons in an array of N coherently coupled two-level atoms, with only the two end atoms interacting with a waveguide at distinct spatial points. The chain serves as a giant-atom-like scatterer with internal collective modes. Using the real-space approach, analytical expressions for the scattering amplitudes are obtained. For the ideal case without atomic loss, the transmission is reciprocal and can be modulated by the relative local coupling phase, the accumulated propagation phase, the interatomic hopping strength, and the photon–atom detuning. We further observe that the oscillatory behavior of the transmission spectrum becomes more pronounced as the number of atoms increases. When atomic loss into nonguided modes is included, phase-dependent interference gives rise to dissipation-assisted nonreciprocal transmission. By appropriately tuning the phase factors, the atomic loss rate, and the hopping strength, one can achieve maximal nonreciprocity, corresponding to complete suppression of transmission for one incident direction. These results establish a flexible platform for engineering directional single-photon transport in guided-wave quantum electrodynamics.
Abstract We theoretically investigate single-photon scattering and nonreciprocal transmission in a coupled resonator waveguide which is coupled to a driven three-level giant atom via two distant sites. In our system, the local coupling phases are introduced to induce intriguing interference effects. As a result, the phase difference can serve as a sensitive controller for the photon scattering. It is found that the photon scattering properties can be effectively tailored by the size of the giant atom, the driving field and the phase difference. Intriguingly, by carefully tuning the parameters such as the atomic dissipation and the phase difference, a perfect nonreciprocal single-photon transmission can be realized. Additionally, the photon frequency can be adjusted by modulating Rabi frequency of the driving field. These results have significant potential for the development of nonreciprocal optical devices using the giant-atom configuration.
Abstract Controllable single-photon scattering in a one-dimensional waveguide coupled to a Jaynes–Cummings structure containing a time-modulated two-level atom interacting with a single-mode cavity is investigated. The photon transmission and reflection amplitudes are calculated by using an effective Floquet Hamiltonian in real space. The results show that the coupling between the atom and the cavity mode can dynamically be tuned via periodically modulating the atomic transition frequency. As a consequence, the scattering behaviors of the waveguide photons can be actively manipulated, and a controllable single-photon switch with high on-off ratio could be realized. More interestingly, the switch works well within a wide frequency region, i.e., the transmission of both resonant and off-resonant waveguide photons can be effectively switched on or off with appropriate system parameters. Furthermore, the proposed dynamically tunable switching scheme is robust against atomic dissipation associated with the help of atom-cavity coupling mismatch. Such single-photon device can be used as an elementary unit for various quantum information processing.