Quasi-anti-parity–time-symmetric single-resonator micro-optical gyroscope with Kerr nonlinearity

Parity–time(PT) and quasi-anti-parity–time(quasi-APT) symmetric optical gyroscopes have been proposed recently which enhance Sagnac frequency splitting. However, the operation of gyroscopes at the exceptional point(EP) is challenging due to strict fabrication requirements and experimental uncertainties. We propose a new quasi-APT-symmetric micro-optical gyroscope which can be operated at the EP by easily shifting the Kerr nonlinearity. A single resonator is used as the core sensitive component of the quasi-APT-symmetric optical gyroscope to reduce the size, overcome the strict structural requirements and detect small rotation rates. Moreover, the proposed scheme also has an easy readout method for the frequency splitting. As a result, the device achieves a frequency splitting 10~5 times higher than that of a classical resonant optical gyroscope with the Earth's rotation. This proposal paves the way for a new and valuable method for the engineering of micro-optical gyroscopes.

A nearly deterministic scheme for generation of multiphoton GHZ states with weak cross-Kerr nonlinearity

We propose a scheme to generate polarization-entangled multiphoton Greenberger-Horne^Zeilinger （GHZ） states based on weak cross-Kerr nonlinearity and subsequent homodyne measurement. It can also be generalized to produce maximally N-qubit entangled states. The success probabilities of our schemes are almost equal to 1.

An analytical model for cross-Kerr nonlinearity in a four-level N-type atomic system with Doppler broadening

We present an analytical model for cross-Kerr nonlinear coefficient in a four-level N-type atomic medium under Doppler broadening.The model is applied to87 Rb atoms to analyze the dependence of the cross-Kerr nonlinear coefficient on the external light field and the temperature of atomic vapor.The analysis shows that in the absence of electromagnetically induced transparency(EIT)the cross-Kerr nonlinear coefficient is zero,but it is significantly enhanced when the EIT is established.It means that the cross-Kerr effect can be turned on/off when the external light field is on or off.Simultaneously,the amplitude and the sign of the cross-Kerr nonlinear coefficient are easily changed according to the intensity and frequency of the external light field.The amplitude of the cross-Kerr nonlinear coefficient remarkably decreases when the temperature of atomic medium increases.The analytical model can be convenient to fit experimental observations and applied to photonic devices.

Two-qubit and three-qubit controlled gates with cross-Kerr nonlinearity

Schemes for two-qubit and three-qubit controlled gates based on cross-Kerr nonlinearity are proposed in this paper.The probability of the success of these gates can be increased by quantum nondemolition detectors,which are used to judge which paths the signal photons pass through.These schemes are almost deterministic and require no ancilla photon.The advantages of these gates over the existing ones include less resource consumption and a higher probability of success,which make our schemes more feasible with current technology.

Generation of a four-particle entangled state via cross-Kerr nonlinearity

We propose a scheme for generating a genuine four-particle polarisation entangled state ｜χ^00） that has many interesting entanglement properties and potential applications in quantum information processing. In our scheme, we use the weak cross-Kerr nonlinear interaction between field-modes and the non-demolition measurement method based on highly efficient homodyne detection, which is feasible under the current experiment conditions.

Enhancement of Kerr nonlinearity with vanishing absorption in a tripod scheme

The giant enhancement of Kerr nonlinearity in a four-level tripod type system is investigated theoretically. By tuning the value of the Rabi frequency of the coherent control field, owing to the double dark resonances, the giantenhanced Kerr nonlinearity can be achieved within the right transparency window. The influence of Doppler broadening is also discussed.

Rectification effect in asymmetric Kerr nonlinear medium

Based on the transfer matrix method, the recursion of an electromagnetic wave propagating in an asymmetric Kerr nonlinear medium is analytically formulated, from which the rectification effect is clearly presented. The effects on the rectification regioh of the linear part and nonlinear coefficient of permittivity are both studied, and the energy densities before and after rectification are discussed. We use a rectifying factor to describe the intensity of the rectification effect. The result shows that every transmission peak is divided into two parts when the symmetry is broken, and nonlinear asymmetry has a more significant effect on the rectification effect than the linear asymmetry. The rectification intensity and area will be enlarged when the asymmetry factor is increased in a certain range.

Enhanced Kerr nonlinearity in a left-handed three-level atomic system driven by a bichromatic field

China） Enhanced Kerr nonlinearity in a left-handed atomic system consisting of three levels driven by a bichromatic field is presented in this paper. Based on bichromatic field coherence, the real parts of the permittivity and permeability can obtain negative values simultaneously in the same detuning frequency region. By adjusting the frequency difference and the Rabi frequencies of the bichromatic field, the multi-band left-handed behavior of the presented atomic metamaterial is exhibited. Meanwhile, the enhanced Kerr nonlinearity can be realized in this multi-band left-handed three-level atomic system. It is shown that the third-order susceptibility possesses focusing or defocusing properties in the same frequency band.

Influence of a Single Frequency Electromagnetic Wave on Energy Spectrum of Nonpolariton System in a Kerr Nonlinear Blackbody

In a Kerr nonlinear blackbody, bare photons with opposite wave vectors and helieities are bound into pairs and unpaired photons are transformed into a different kind of quasiparticle, the nonpolariton. The present paper investigates the influence of a single frequency electromagnetic wave on the energy spectrum of the nonpolariton system. We find that the wave can lead to an energy shift of nonpolaritons. Moreover, we calculate the first-order energy shift on certain conditions.

Low-threshold bistable reflection assisted by oscillating wave interaction with Kerr nonlinear medium

Owing to the enormously enhanced oscillating wave,a minute variation of the incident light intensity will give rise to a change in the dielectric constant of the Kerr nonlinear medium and lead to a bistable reflection with an ultra-low threshold intensity,which is closely related to the angle of incidence and the thickness of the Kerr nonlinear medium.The criterion for the existence of optical bistability is derived.Our bistability scheme is simple and not limited to the TM-polarization.

Giant Kerr nonlinearity induced by interacting quantum coherences from decays and incoherent pumping

A scheme for generating the giant enhancement of the Kerr nonlinearity in a four-level system with the quantum coherences from the decays and the incoherent pumping is proposed. Compared with that generated in a general four- level system, the Kerr nonlinearity can be enhanced by several orders of magnitude with vanishing linear absorption. By using the numerical results, we show that the remarkable enhancement should be attributed to the interaction of the quantum coherences from the decays and the incoherent pumping.

Enhanced Kerr Nonlinearities Caused by Cross Talk Between Optical and Microwave Transitions

We investigate the enhanced Kerr nonlinearities in four-level atomic vapors driven by a coupling,probe andmicrowave fields.Under the optical one-photon and two-photon resonant conditions,the linear and nonlinear responsesof the weak probe field can be modified by the cross talk among optical and microwave transitions.The enhanced Kerrnonlinearity can form bright optical solitons of the probe field.

Study of Nonpolaritons in a Kerr Nonlinear Optical Resonator

We find that in a Kerr nonlinear optical resonator, the photon system possesses a new kind of quasiparticle, the nonpolariton. The existence of nonpolaritons should be testified by observing the energy density dependence of the velocity and squeezing of nonpolaritons. As we have investigated, the transition energy density of a Kerr nonlinear optical resonator is larger than that of a normal state.

Complete four-photon cluster-state analyzer based on cross-Kerr nonlinearity

We propose a method to construct an optical cluster-state analyzer based on cross-Kerr nonlinearity combined with linear optics elements. In the scheme, we employ two four-qubit parity gates and the controlled phase gate （CPG） from only the cross-Kerr nonlinearity and show that all the orthogonal four-qubit cluster states can be completely identified. The scheme is significant for the large-scale quantum communication and quantum information processing networks. In addition, the scheme is feasible and deterministic under current experimental conditions.

Generation of hyperentangled four-photon cluster state via cross-Kerr nonlinearity

We propose a scheme for generating a hyperentangled four-photon cluster state that is simultaneously entangled in polarization modes and spatial modes. This scheme is based on linear optical elements, weak cross-Kerr nonlinearity, and homodyne detection. Therefore, it is feasible with current experimental technology.

Generating a four-photon polarization-entangled cluster state with homodyne measurement via cross-Kerr nonlinearity

We propose a protocol to generate a four-photon polarization-entangled cluster state with cross-Kerr nonlinearity by using the interference of polarized photons. The protocol is based on optical elements, cross-Kerr nonlinearity, and homodyne measurement, therefore it is feasible with current experimental technology, The success probability of our protocol is optimal, this property makes our protocol more efficient than others in the applications of quantum communication.

Bidirectional quantum teleportation of unknown photons using path-polarization intra-particle hybrid entanglement and controlled-unitary gates via cross-Kerr nonlinearity

We propose an arbitrary controlled-unitary （CU） gate and a bidirectional quantum teleportation （BQTP） scheme. The proposed CU gate utilizes photonic qubits （photons） with cross-Kerr nonlinearities （XKNLs）, X-homodyne detectors, and linear optical elements, and consists of the consecutive operation of a controlled-path （C-path） gate and a gathering-path （G- path） gate. It is almost deterministic and feasible with current technology when a strong coherent state and weak XKNLs are employed. Based on the CU gate, we present a BQTP scheme that simultaneously teleports two unknown photons between distant users by transmitting only one photon in a path-polarization intra-particle hybrid entangled state. Consequently, it is possible to experimentally implement BQTP with a certain success probability using the proposed CU gate.

Implementation of nonlocal Bell-state measurement and quantum information transfer with weak Kerr nonlinearity

We propose a protocol to implement the nonlocal Bell-state measurement, which is nearly determinate with the help of weak cross-Kerr nonlinearities and quantum non-destructive photon number resolving detection. Based on the nonlocal Bell-state measurement, we implement the quantum information transfer from one place to another. The process is different from conventional teleportation but can be regarded as a novel form of teleportation without entangled channel and classic communication.

Bidirectional transfer of quantum information for unknown photons via cross-Kerr nonlinearity and photon-number-resolving measurement

We propose an arbitrary controlled-unitary （CU） gate and a bidirectional transfer scheme of quantum information （BTQI） for unknown photons. The proposed CU gate utilizes quantum non-demolition photon-number-resolving measure- ment based on the weak cross-Kerr nonlinearities （XKNLs） and two quantum bus beams; the proposed CU gate consists of consecutive operations of a controlled-path gate and a gathering-path gate. It is almost deterministic and is feasible with current technology when a strong amplitude of the coherent state and weak XKNLs are employed. Compared with the existing optical multi-qubit or controlled gates, which utilize XKNLs and homodyne detectors, the proposed CU gate can increase experimental realization feasibility and enhance robustness against decoherence. According to the CU gate, we present a BTQI scheme in which the two unknown states of photons between two parties （Alice and Bob） are mutually swapped by transferring only a single photon. Consequently, by using the proposed CU gate, it is possible to experimentally implement the BTQI scheme with a certain probability of success.

Enhanced Kerr nonlinearity in a quantized four-level graphene nanostructure

In this paper, a new model is proposed for manipulating the Kerr nonlinearity of right-hand circular probe light in a monolayer of graphene nanostructure. By using the density matrix equations and quantum optical approach, the third-order susceptibility of probe light is explored numerically. It is realized that the enhanced Kerr nonlinearity with zero linear absorption can be provided by selecting the appropriate quantities of controllable parameters, such as Rabi frequency and elliptical parameter of elliptical polarized coupling field. Our results may be useful applications in future all-optical system devices in nanostructures.