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Physical Review A

Generation of nonreciprocal single photons in the chiral waveguide-cavity-emitter system

Wen-ju Gu, Lei Wang, Zhen Yi, Lihui Sun

Published Oct 28, 2022• 14 citations
Publisher

Abstract

We investigate the generation of nonreciprocal single photons in the chiral waveguide-cavity-emitter system. Due to the chirality of light-emitter interactions, photons in the left direction couple to a cavity which induces only linear optical effects, while photons in the right direction couple to a cavity-emitter system which can generate optical nonlinearity. In the regime of single-photon transmission, photons in the left direction are absorbed by the cavity at the resonance frequency, while photons in the right direction are transmitted due to the Rabi splitting. In the regime of two-photon transmission, optical linearity in the left direction cannot produce photon-photon interactions and does not change the statistics of photons. However, the effective repulsive interaction between photons can be produced by the optical nonlinearity in the right direction, suppressing two-photon transmission (photon blockade). Physically, the photon-photon bound state, which emerges due to the strong-photon-photon correlation mediated by the cavity-emitter system, plays a key role in generation of photon blockade at the resonance frequency. As a result, nonreciprocal single photons can be realized in the combination of single-photon transmission and photon blockade at the resonance frequency. Additionally, photon-photon interactions are sensitive to the width of the wave packet since photons should coincide at the interaction site.

DOI
10.1103/physreva.106.043722

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We investigate the generation of nonreciprocal single photons in the chiral waveguide-cavity-emitter system. Due to the chirality of light-emitter interactions, photons in the left direction couple to a cavity which induces only linear optical effects, while photons in the right direction couple to a cavity-emitter system which can generate optical nonlinearity. In the regime of single-photon transmission, photons in the left direction are absorbed by the cavity at the resonance frequency, while photons in the right direction are transmitted due to the Rabi splitting. In the regime of two-photon transmission, optical linearity in the left direction cannot produce photon-photon interactions and does not change the statistics of photons. However, the effective repulsive interaction between photons can be produced by the optical nonlinearity in the right direction, suppressing two-photon transmission (photon blockade). Physically, the photon-photon bound state, which emerges due to the strong-photon-photon correlation mediated by the cavity-emitter system, plays a key role in generation of photon blockade at the resonance frequency. As a result, nonreciprocal single photons can be realized in the combination of single-photon transmission and photon blockade at the resonance frequency. Additionally, photon-photon interactions are sensitive to the width of the wave packet since photons should coincide at the interaction site.
We study the nonreciprocal properties of transmitted photons in a chiral waveguide quantum electrodynamics (QED) system, including single- and two-photon transmissions and second-order correlations. For the single-photon transmission, the nonreciprocity is induced by the effects of chiral coupling and atomic dissipation in the weak coupling region. It vanishes in the strong coupling regime when the effect of atomic dissipation becomes ignorable. In the case of two-photon transmission, there exist two ways of going through the emitter: independently as plane waves and formation of bound state. Besides the nonreciprocal behavior of plane waves, the bound state that differs in two directions also alters transmission probabilities. In addition, the second-order correlation of transmitted photons depends on the interference between plane wave and bound state. The destructive interference leads to the strong antibunching in the weak coupling region, while the effective formation of bound state leads to the strong bunching in the intermediate coupling region. However, the negligible interactions for left-propagating photons hardly change the statistics of the input coherent state.
We introduce a method to achieve nonreciprocal photon blockade in an optical resonator that is chirally coupled to a two-level atom. This approach enables single-excitation and two-excitation resonant conditions to be simultaneously satisfied. The atom-uncoupled optical mode can be blocked with eliminating its two-photon excitation by judiciously selecting parameters, e.g., the optical coupling strength. The chiral interaction between the resonator mode and the atom leads to different optimal parameter conditions for generating photon blockade in the two opposite drivings. This offers a natural way to realize nonreciprocal photon blockade. The nonreciprocity achieved by the chiral cavity-atom interaction diminishes the experimental difficulty by eliminating the need to rotate the resonator. The blockade mode achieves very high purity of single-photon excitation, as characterized by a second-order correlation function of ${g}^{(2)}(0)\ensuremath{\sim}{10}^{\ensuremath{-}4}$. In particular, in the nonreciprocal regime, the mean number of photons is significantly higher where photon blockade occurs compared to the general Jaynes-Cummings case. Our findings are particularly relevant for the development of quantum nonreciprocal devices and their applications in quantum information processing, including chiral networks.
Chiral quantum optics is a new research area in light-matter interaction that depends on the direction of light propagation and offers a new path for the quantum regulation of light-matter interactions. In this paper, we study a spinning Kerr-type microresonator coupled with Λ-type atom ensembles, which are driven in opposite directions to generate asymmetric photon statistics. We find that a photon blockade can only be generated by driving the spinning resonator on right side without driving the spinning microresonator from the left side, resulting in chirality. The coupling strength between system modes can be precisely controlled by adjusting the detuning amount of the atomic pump field. Because of the splitting of the resonant frequency generated by the Fizeau drag, the destructive quantum interference generated in right side drive prevents the nonresonant transition path of state ∣1,0〉 to state ∣2,0〉. This direction-dependent chiral quantum optics is expected to be applied to chiral optical devices, single-photon sources and nonreciprocal quantum communications.
Based on the scattering matrix method, we theoretically demonstrate that the chiral interaction can induce the almost perfect photon blockade (PB) in the waveguide-cavity quantum electrodynamics system. The mechanism relies on the multiphoton path's interference within the waveguide, which is clearly shown by the analytic parameter regime for g^{(2)}(0)≈0. When N cavities are introduced into the system, there are N optimal parameter points accordingly for the almost perfect PB, where the required lowest chirality decreases exponentially with increasing N, and these optimal points are robust against disorder in the system's frequencies. Under resonant driving and fixed chirality conditions, the output light depends solely on the parity of N (N≥2), with a coherent state emerging for even numbers of cavities and a single-photon state for odd numbers. Our Letter offers an alternative route for achieving almost perfect PB effects with high single-photon transmission by employing the chirality of system, with potential application in the on-chip single-photon source with integrability.
We study the controllable single-photon scattering via a one-dimensional waveguide which is coupled to a two-level emitter and a single-mode cavity simultaneously. The emitter and the cavity are also coupled to each other and form a three-level system with cyclic transitions within the zero- and single-excitation subspaces. As a result, the phase of emitter-cavity coupling strength serves as a sensitive control parameter. When the emitter and cavity locate at the same point of the waveguide, we demonstrate the Rabi splitting and quasidark-state-induced perfect transmission for the incident photons. More interestingly, when they locate at different points of the waveguide, a controllable nonreciprocal transmission can be realized and the nonreciprocity is robust to the weak coupling between the system and environment. Furthermore, we demonstrate that our theoretical model is experimentally feasible with currently available technologies.
We investigate chiral emission and the single-photon scattering of spinning cavities coupled to a meandering waveguide at multiple coupling points. It is shown that nonreciprocal photon transmissions occur in the cavities-waveguide system, which stems from interference effects among different coupling points, and frequency shifts induced by the Sagnac effect. The nonlocal interference is akin to the mechanism in giant atoms. In the single-cavity setup, by optimizing the spinning velocity and number of coupling points, the chiral factor can approach 1, and the chiral direction can be freely switched. Moreover, destructive interference gives rise to the complete photon transmission in one direction over the whole optical frequency band, with no analogy in other quantum setups. In the multiple-cavity system, we also investigate the photon transport properties. The results indicate a directional information flow between different nodes. Our proposal provides a novel way to achieve quantum nonreciprocal devices, which can be applied in large-scale quantum chiral networks with optical waveguides.