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Optics Express

Realization of nonreciprocal photon statistics by manipulating the quantum nonlinearity of cold atoms in an asymmetric cavity

Pengfei Yang, Zhihui Wang, Qing Fan, Chen Yang, Pengfei Zhang, Gang Li, Tiancai Zhang

Published Jul 16, 2024• 1 citation
Publisher

Abstract

(τ) of the transmitted probe light from the cavity is determined by the nonlinearity of the atom in the cavity. Therefore, the system provides a platform for controlling the photon statistics by manipulating nonlinearity. In this paper, we experimentally demonstrate nonreciprocal quantum statistics in a cavity QED system with several atoms strongly coupled to an asymmetric optical cavity, which is composed of two mirrors with different transmittivities. When the direction of the probe light is reversed, the intracavity light field alternates to a different level. Distinct photon statistics are then observed due to the quantum nonlinearity associated with strongly coupled atoms. Sub-Poissonian photon-number statistics for forward light and a Poissonian distribution for backward light are then realized. Our work provides an effective approach for realizing nonreciprocal quantum devices, which have potential applications in the unidirectional generation of nonclassical light fields and quantum sensing.

DOI
10.1364/oe.532908

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(τ) of the transmitted probe light from the cavity is determined by the nonlinearity of the atom in the cavity. Therefore, the system provides a platform for controlling the photon statistics by manipulating nonlinearity. In this paper, we experimentally demonstrate nonreciprocal quantum statistics in a cavity QED system with several atoms strongly coupled to an asymmetric optical cavity, which is composed of two mirrors with different transmittivities. When the direction of the probe light is reversed, the intracavity light field alternates to a different level. Distinct photon statistics are then observed due to the quantum nonlinearity associated with strongly coupled atoms. Sub-Poissonian photon-number statistics for forward light and a Poissonian distribution for backward light are then realized. Our work provides an effective approach for realizing nonreciprocal quantum devices, which have potential applications in the unidirectional generation of nonclassical light fields and quantum sensing.
Optical nonreciprocity is important in photonic information processing to route the optical signal or prevent the reverse flow of noise. By adopting the strong nonlinearity associated with a few atoms in a strongly coupled cavity QED system and an asymmetric cavity configuration, we experimentally demonstrate the nonreciprocal transmission between two counterpropagating light fields with extremely low power. The transmission of 18% is achieved for the forward light field, and the maximum blocking ratio for the reverse light is 30 dB. Though the transmission of the forward light can be maximized by optimizing the impedance matching of the cavity, it is ultimately limited by the inherent loss of the scheme. This nonreciprocity can even occur on a few-photon level due to the high optical nonlinearity of the system. The working power can be flexibly tuned by changing the effective number of atoms strongly coupled to the cavity. The idea and result can be applied to optical chips as optical diodes by using fiber-based cavity QED systems. Our work opens up new perspectives for realizing optical nonreciprocity on a few-photon level based on the nonlinearities of atoms strongly coupled to an optical cavity.
Optical non-reciprocity for weak light field is particularly important for chip-based photonic and quantum information process. By adopting the strong nonlinearity associated with a few atoms in a strongly coupled cavity QED system and an asymmetric cavity configuration, we experimentally demonstrate the nonreciprocal transmission between two counterpropagating light fields with extremely low power. The system can be further manipulated to realize a non-reciprocal cavity polariton. Such that an optical isolation exceeds 30dB on single-quanta level and non-reciprocal non-classical statistics with coherent probe lights can be obtained, manifesting the quantum nature of the non-reciprocal polaritons.
Optical nonreciprocity plays an essential role in optical information communication and information processing. Based on electromagnetically induced transparency, a nonreciprocal cavity dark-state polariton (DSP) could be achieved using spin-biased cold atoms. The DSP induces a nonreciprocal window with high transmission and low insertion loss around the cavity resonant frequency. By decreasing the strength of the control field, the contribution of the atom excitation dominates the behavior of the DSP, which exhibits a narrow cavity linewidth and thus a long lifetime of cavity photons in the form of the DSP. Further, we investigate the nonreciprocity for the statistical properties of the system in the single-atom (N=1N=1N=1) and multiatom (N>1N>1N>1) cases. Due to the existence of DSP, the photon statistics leads to totally different profiles for the light propagating in both directions in the two cases. In the single-atom (N=1N=1N=1) case, the light in the form of DSP shows apparent sub-Poissonian distribution simultaneously with relatively high transmission and a narrow bandwidth corresponding to the one-photon excitation due to quantum interference. Such a quasiparticle may provide a platform for novel applications in nonreciprocal quantum devices and quantum simulation.
We propose a scheme to realize tunable and strong nonreciprocal photon blockade (PB) in an asymmetric Fabry-Pérot cavity. The setup consists of a single-mode optical cavity trapping a two-level atom, with the cavity coherently driven by a laser and the atom pumped by an auxiliary control field of the same frequency. By engineering quantum interference between multiple excitation pathways by adjusting the amplitude and relative phase of the control laser, we identify two distinct optimal control conditions that enable directional suppression of two-photon states. Under optimal control conditions, strong nonreciprocal PB is achieved, with a nonreciprocal ratio exceeding 30 dB over a broad operational bandwidth. The proposed protocol requires only standard coherent laser sources and is compatible with current cavity QED experimental setups, offering a practical and scalable platform for nonreciprocal quantum photonics.
Abstract Breaking the time‐reversal symmetry of light is of great importance for fundamental physics and has attracted increasing interest in the study of non‐reciprocal photonic devices. Here, a chiral cavity quantum electrodynamics system with multiple atoms strongly coupled to a Fabry–Pérot cavity is experimentally demonstrated. By polarizing the internal quantum state of the atoms, the time‐reversal symmetry of the atom‐cavity interaction is broken. The strongly coupled atom‐cavity system can be described by non‐reciprocal quasiparticles, that is, the cavity polariton. When it works in the linear regime, the inherent nonreciprocity makes the system work as a single‐photon‐level optical isolator. Benefiting from the collective enhancement of multiple atoms, an isolation ratio exceeding 30 dB on the single‐quanta level (≈ 0.1 photon on average) is achieved. The validity of the non‐reciprocal device under zero magnetic field and the reconfigurability of the isolation direction are also experimentally demonstrated. Moreover, when the cavity polariton works in the nonlinear regime, the quantum interference between polaritons with weak anharmonicity induces non‐reciprocal nonclassical statistics of cavity transmission from coherent probe light.
We present a proposal to control and improve the nonclassicality of photons in a single-atom cavity-QED system with a strong coupling strength, where the atom is directly driven by external fields. Exploring the eigenvalues and the corresponding eigenstates of the system, we show that the dressed states can be optically manipulated by changing the control field intensity. In particular, tuning the control field frequency to be resonant with the one-photon excitation state, we show that the nonclassicality of cavity photons arising from the two-photon blockade can be actively controlled. We also show that there exists a magic control field Rabi frequency at which the two-photon blockade phenomenon can be significantly improved. The work presented here provides an optical method to control the statistical features of the cavity field that could find utility in nonclassical light generation, photon gateway operation, and exotic quantum-state generation.