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 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 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.
(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.
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.
In analog to counterparts widely used in electronic circuits, all optical non-reciprocal devices are basic building blocks for both classical and quantum optical information processing. Approaching the fundamental limit of such devices, where the propagation of a single photon exhibits a good non-reciprocal characteristic, requires an asymmetric strong coupling between a single photon and a matter. Unfortunately it has been not realized yet. Here, we propose and experimentally realize a quantum non-reciprocity device with low optical losses and a high isolation of larger than 14 dB based on the cold atoms. Besides, the non-reciprocal transmission of a quantum qubit and non-reciprocal quantum storage of a true single photon are also realized. All results achieved would be very promising in building up quantum non-reciprocal devices for quantum networks.
Abstract Hot atoms can exhibit non-magnetic optical non-reciprocal transmission due to their chiral properties, which are characteristic of most alkali metal atoms. In fact, the nonreciprocity in hot atoms depends on the propagation direction of the coupling field due to the Doppler effect. Herein, the reciprocal to non-reciprocal conversion based on the single- and double-dark states is realized by controlling the bidirectional coupling fields in a three-level electromagnetically induced transparent medium coupled with a ring cavity. Tuning the frequency difference between the two coupling fields causes the multi-frequency-channel reciprocity and nonreciprocity manipulation to occur. The experimental proof can be applied to quantum communications and quantum networks, such as optical transistors, all-optical switching or routing and logic gate operation.
Owing to the potential applications in all-optical quantum information processing and quantum optical networks, magnet-free optical non-reciprocity transmission has attracted great interest and has been studied in many fields, such as parity-time-symmetry enhanced nonlinearity, optomechanical systems, photonic crystal, cold atomic Bragg lattices, chiral quantum optics, and hot atoms. In particular, the random thermal motion of hot atoms can be a useful resource to realize optical non-reciprocity. Here in this work, based on the susceptibility-momentum-locking of atomic thermal motion and the strong coupling characteristics of cavities, a magnetic-free optical reciprocity-nonreciprocity transmission conversion scheme is designed and realized through the atom-cavity compound system. Theoretical and experimental analysis show that the coupling field conditions determine the nonreciprocity of the system. Under the action of single traveling-wave field, the nonreciprocity in hot atoms depends on the propagation direction of the coupling field due to the Doppler effect. Therefore, by changing the opening and closing of the opposite coupling field, the two-way single channel optical nonreciprocal transmission based on intracavity electromagnetically induced transparency can be controlled. When the two coupling fields propagate simultaneously in the opposite directions, however, the cavity transmission changes from single-dark-state to double-dark-state peaks, in which the reciprocity outputs depend on the frequency difference between the two coupling fields. By tuning the frequency difference, the two-way multi-channel reciprocal-nonreciprocal transmission regulation based on double dark polar peaks can be realized. The study can be applied to all-optical quantum devices and quantum information processing, such as optical transistors, optical switching and routing, and quantum gate manipulation.