We study nonreciprocal single-photon scattering in a giant-spin-ensemble (GSE)--waveguide magnonics system where the GSE constructed by a yttrium iron garnet sphere interacts twice with the waveguide via two separated coupling points. It is shown that the generation of nonreciprocity arises from the synergy of the breaking of time-reversal symmetry induced by the chiral coupling and the intrinsic dissipation of the magnon mode in the case of a single waveguide. The accumulated phase caused by the photon propagating between coupling points can be a powerful tool to control nonreciprocity due to quantum interference effects. Compared to the Markovian regime, single-photon transmission exhibits peculiarly nonreciprocal properties in the non-Markovian regime. Multiple narrow nonreciprocal transmission windows are observed. Non-Markovianity can break the decoupling phenomenon of the Markovian regime and non-Markovianity-induced nonreciprocity is demonstrated. We extend the study of nonreciprocity to the GSE coupled to a double-waveguide structure to explore the design of quantum devices. A high-efficiency and tunable multifrequency single-photon targeted router and circulator with narrow operational bandwidth are achieved. Our results provide an effective avenue for single-photon manipulation and have potential applications in designing magnon-based quantum devices and constructing an integrated quantum network.
We study nonreciprocal single-photon scattering in a giant-spin-ensemble (GSE)--waveguide magnonics system where the GSE constructed by a yttrium iron garnet sphere interacts twice with the waveguide via two separated coupling points. It is shown that the generation of nonreciprocity arises from the synergy of the breaking of time-reversal symmetry induced by the chiral coupling and the intrinsic dissipation of the magnon mode in the case of a single waveguide. The accumulated phase caused by the photon propagating between coupling points can be a powerful tool to control nonreciprocity due to quantum interference effects. Compared to the Markovian regime, single-photon transmission exhibits peculiarly nonreciprocal properties in the non-Markovian regime. Multiple narrow nonreciprocal transmission windows are observed. Non-Markovianity can break the decoupling phenomenon of the Markovian regime and non-Markovianity-induced nonreciprocity is demonstrated. We extend the study of nonreciprocity to the GSE coupled to a double-waveguide structure to explore the design of quantum devices. A high-efficiency and tunable multifrequency single-photon targeted router and circulator with narrow operational bandwidth are achieved. Our results provide an effective avenue for single-photon manipulation and have potential applications in designing magnon-based quantum devices and constructing an integrated quantum network.
ABSTRACT We propose a scheme for realizing strong quantum nonreciprocity and nonreciprocal photonic devices mediated by the magnon‐photon coupling phase based on giant magnon molecule in both the Markovian and the non‐Markovian regimes, where the giant magnon molecule is composed of two coupled giant spin ensembles interacting with two waveguides. We reveal the hidden effective chirality of the system and further implement quantum nonreciprocity. In the Markovian regime, the perfect nonreciprocity of single photon transmission can be observed by tuning phase and its various values of work frequency points can be satisfied based on the regulation of magnon‐magnon coupling strength. We obtained a flexible frequency modulation single photon diode. It is also found that single photon targeted router with tunable routing direction and perfectly asymmetrical scattering effects including chiral scattering and nonreciprocal routing are realized. The coordinated modulation of the coupling phases and the accumulated phases caused by photon moving between two coupling points can complete single photon circulator with multiple circulating directions. In the non‐Markovian regime, single photon transmission exhibits multiple narrow nonreciprocal transmission windows. Multi‐frequency single photon targeted router, multiple narrow asymmetrical scattering effects windows, and multi‐frequency single photon circulator are further obtained. In addition, under specific conditions, non‐Markovianity can induce nonreciprocity and asymmetrical scattering effects that cannot occur in the Markovian regime. Non‐Markovianity induced single photon level quantum devices are further designed. Our results provide a promising for on‐chip single photon manipulation and have potential applications in integrated magnon‐based quantum network engineering.
Abstract In this work, we investigate the nontrivial single-photon scattering properties of giant atoms coupled to waveguides that can be an effective platform for realising nonreciprocal and chiral quantum optics. For the two-level giant-atom setup, we identify the condition for nonreciprocal transmission: the external atomic dissipation is further required other than the breaking of time-reversal symmetry by local coupling phases. Especially, in the non-Markovian regime, unconventional revival peaks periodically appear in the reflection spectrum of such a two-level giant-atom system. To explore more interesting scattering behaviours, we further extend the two-level giant-atom system to Δ-type and ∇-type three-level giant atoms coupled to double waveguides without external atomic dissipation. We analyse the different physical mechanisms for the nonreciprocal and chiral scattering properties of the ∆-type and ∇-type giant atoms. Our proposed giant-atom structures have potential applications of high-efficient single-photon targeted router and circulator for quantum information precessing.
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.
Abstract We investigate the single-photon scattering properties of a driven three-level giant atom chirally coupled to two waveguides simultaneously in both the Markovian and the non-Markovian regimes. It is shown that under the Markovian limit, the chiral photon-atom interactions enable nonreciprocal scattering in a single waveguide and targeted photon routing with a probability of 100% in two waveguides, while the presence of the driving field and the giant atom structure introduce a more tunable parameter to manipulate the single-photon scattering behaviors. We also examine how the non-reciprocity and routing capability are influenced by the imperfect chirality and the atomic dissipation. In the non-Markovian regime, we show that the scattering behaviors are more complicated. The non-Markovicity induced non-reciprocity and photon routing are demonstrated in this paper. We believe that those results 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.
Chiral interactions enable directional control of quantum light, providing new routes for nonreciprocal photon dynamics. While previous studies focused on single photon regimes, this work explores the non-Markovian multiphoton regime in a giant nonlinear system nonlocally coupled to a one-dimensional waveguide, with a tunable phase difference breaking parity symmetry. We show that single-photon transport remains reciprocal, but multiphoton dynamics become chiral, generating direction-dependent higher-order correlations and enabling deterministic creation of multiphoton states with nontrivial statistics from a single input direction, even under strong dissipation. The non-Markovian nature allows tuning of transmitted photon statistics via the coupling-point separation. At a specific phase, internal dynamics become Markovian while output photons retain non-Markovian features. Under strong coherent driving, we uncover nonreciprocal dissipative phase transitions and demonstrate how non-Markovianity shapes the critical response. This framework offers a general strategy for controlling chiral multiphoton dynamics in nonlocally coupled waveguide QED systems. Chiral light-matter interactions offer directional control of quantum states. This work demonstrates that a giant quantum emitter with tunable nonlocal coupling to a waveguide enables direction-dependent multiphoton correlations and dissipative phase transitions, providing a route to engineer non-Markovian chiral dynamics.