Polarization-Entanglement Purification for Ideal Sources Using Weak Cross-Kerr Nonlinearity

We propose an entanglement purification protocol (EPP) for ideal entangled photon sources resorting to weak cross-Kerr nonlinearities. The key element of this EPP is the quantum nondemolition detector (QND) which uses weak cross-Kerr nonlinearity effect to generate phase shifts on the coherent states conditionally. By exploiting the double cross-phase modulation (XPM) method in QND, we present an efficient EPP protocol, which reduces the requirement for coupling strength of the cross-Kerr nonlinearity medium. The proposed protocol may open up promising possibilities for the practicability of quantum information processing using weak cross-Kerr nonlinearities.     

Effective protocol for preparation of three-atom Greenberger-Horne-Zeilinger state and W state with the help of cross-Kerr nonlinearity

We propose a protocol to generate a Greenberger-Horne-Zeilinger (GHZ) state andWstate by using simple linear elements and quantum nondemolition detectors (QNDs). With the help of cross-Kerr nonlinearity, our protocol can generate the intended states with only one setup, and the probability of getting a W state is greatly increased when compared with previous schemes [Phys. Rev. A 75 (2007) 044301]. Also, our proposed protocol is realizable in experiments.     

Qudit-type entanglement of continuous variables via weak cross-Kerr non linearity

We propose a protocol for creating arbitrary qudit state (including entangled states) with arbitrary dimensionality in continuous variable system using weak cross-Kerr nonlinearity, linear beamsplitters, detectors not resolving photon numbers, and sources of coherent states. The equation for unique determination of the used coherent states amplitudes is found. The protocol is applicable for creating entangled states at distances of 100 km using cross-Kerr nonlinearity χ ≥ χ _min ≃ 0.01 and optical fiber quantum channel.     

Efficient three-step entanglement concentration for an arbitrary four-photon cluster state

We propose an entanglement concentration protocol to concentrate an arbitrary partially-entangled four-photon cluster state.As a pioneering three-step entanglement concentration scheme,our protocol only needs a single-photon resource to assist the concentration in each step,which makes this protocol more economical.With the help of the linear optical elements and weak cross-Kerr nonlinearity,one can obtain a maximally-entangled cluster state via local operations and classical communication.Moreover,the protocol can be iterated to obtain a higher success probability and is feasible under current experimental conditions.     

Direct measurement of the concurrence for two-photon polarization entangled pure states by parity-check measurements

We present a protocol for directly measuring the concurrence of a two-photon polarization entangled pure or mixed state without prior quantum state tomography. By parity-check measurements and simple operations on two copies of the two-photon polarization entangled pure state, the concurrence is encoded in the total probability of picking up the odd parity states from the signal states. This protocol makes use of highly efficient homodyne detection, and it could be feasible in the near future with the help of the weak cross-Kerr nonlinearity. Moreover, our protocol can be used in a distributed fashion to directly determine the entanglement of remote states, which may find its important applications in quantum communication.     

交叉克尔非线性对二阶非线性诱导透明的影响

考虑耦合介质存在交叉克尔非线性的情形下,研究了交叉克尔效应对耦合双谐振腔中二阶非线性诱导透明的影响.首先给出了描述体系理论模型的哈密顿量,再通过对海森堡-朗之万方程进行线性化,得到了探测场的透射率,进而得出系统的吸收和色散关系.研究结果表明,在交叉克尔非线性强度较小时,可忽略其对诱导透明的影响;随着交叉克尔非线性强度的增大,诱导透明窗口宽度随之快速变窄.此外,吸收曲线中还出现了双吸收峰.进一步增强交叉克尔非线性,导致原本出现的诱导透明消失,并在新吸收峰处产生了新的诱导透明,新的诱导透明的吸收零点位置随着交叉克尔非线性增加而向左偏移.这些结果可能在不透明介质的窄窗口光传输和提高光学腔的性能方面提供一些参考.     

Complete Analysis of Four-Photon χ-Type Entangled State via Cross-Kerr Nonlinearity

We propose an efficient method to construct an optical four-photon |χ> state analyzer via the cross-Kerr nonlinearity combined with linear optical elements. In this protocol, two four-qubit parity-check gates and two controlled phase gates are employed. We show that all the 16 orthogonal four-qubit |χ> states can be completely discriminated with our apparatus. The scheme is feasible and realizable with current technology. It may have useful potential applications in quantum information processing which based on |χ> state.     

用弱交叉Kerr非线性实现光子极化纠缠Bell态的完全区分

基于相干态和信号位的光子数态与弱交叉Kerr非线性相互作用后,会在相干态上产生相位变化,并结合极化分束器构造了一个奇偶校验测量装置. 用零差探测器对相干态的相位变化进行测量,实现对Bell态的非破坏区分. 再利用控制非门和斜置的极化分束器对两信号位光子进行控制非操作和单光子测量,完成对四个Bell态的完全区分. 用到的弱交叉Kerr非线性增加了区分方案在实验上实现的可行性.     

Efficient W polarization state distribution over an arbitrary collective-noise channel with cross-Kerr nonlinearity

We propose an efficient protocol for W polarization entangled state distribution over an arbitrary collective-noise channel with the help of the cross-Kerr nonlinearity. The entangled state in the frequency degree of freedom, which suffers little from the noise in an optical fiber, is used in the present protocol. The frequency entanglement can be transferred into polarization entanglement with the success probability of 100%. So, the three parities can share the maximally W polarization state with local operations and polarization independent wavelength division multiplexers which can erase distinguishability for frequency.     

Effective Protocol for Generation of the Greenberger-Horne-Zeilinger State and Implementation of Controlled Phase Gate with Cross-Kerr Nonlinearity

A protocol for generation of GHZ state and implementation of controlled phase gate is proposed in this paper. With the help of cross-Kerr nonlinearity, we can obtain GHZ state of photons with the successful probability of 100 % by nondemdition measurement. Moreover, a similar method can be exploited to implement the controlled phase gate with high efficiency by adding a new device.     

Quantum teleportation of an entangled 2-photon polarization state with preparing determinately two Bell states based on cross-Kerr nonlinearity

A scheme, in which cross-Kerr nonlinearity is used for the Bell-state measurements and preparation of the resource of entanglement, is proposed for teleporting an entangled 2-photon state by using two polarization-photon Bell states as quantum channel based on cross-Kerr nonlinearity combined with linear optics elements such as polarization beam splitters and half wave plates. Teleportation of the entangled 2-photon polarization state can realized with certainty in principle.     

原子消相干对四能级EIT系统中非线性效应的影响

文章在理论上研究了原子消相干速率对Rb原子四能级Tripod系统中EIT增强的交叉Kerr非线性的影响.结果表明,交叉Kerr非线性效应随着原子消相干速率的减小而增大.当两基态之间消相干速率γ1从2.5 MHz减小到0.2 MHz时,交叉Kerr非线性折射率可增强一个数量级.     

Complete Bell-state and Greenberger–Horne–Zeilinger-state nondestructive detection based on simplified symmetry analyzer

We present a simplified symmetry analyzer (SA) with cross-Kerr nonlinearity, quantum non-demolition photon number measurement and basic optical elements. Based on the present symmetry analyzer (SA), all the Bell states can be discriminated nondestructively with nearly unity probability. In addition, with the help of cross-phase modulation (XPM) induced by giant cross-Kerr nonlinearity, three-photon Greenberger–Horne–Zeilinger (GHZ) state can also be discriminated determinately and nondestructively, which is supposed to be meaningful in quantum information processing.     

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.     

Highly efficient scheme for the preparation of four-photon polarization entangled state via quantum non-demolition measurement with classical feed-forward

A simple and efficient scheme is proposed to prepare a four-photon entangled state, which can be used as a resource for realizing a controlled-NOT (CNOT) gate pointed out by Gottesman and Chuang [Nature 402 (1999) 390], with the help of the cross-Kerr nonlinearity. The distinct feature of the present scheme is its preparation with near unity success probability and near perfect fidelity. It is not necessary in the present scheme that the cross-Kerr nonlinearity is very large because the weak nonlinearity can be compensated by using a coherent light laser probe beam with very large amplitude. This makes us more confident in the feasibility of the proposed scheme.     

Effective schemes for preparation of Greenberger–Horne–Zeilinger and W maximally entangled states with cross-Kerr nonlinearity and parity-check measurement

Schemes to generate Greenberger–Horne–Zeilinger and W maximally entangled states of distant photons with the help of cross-Kerr nonlinearity and parity-check measurement are proposed in this paper. The schemes are based on optical elements, single polarization photons, cross-Kerr nonlinearity, and the conventional photon detectors, which are feasible with existing experimental technology. The schemes are quite different a higher success probability, without the resorting to collective unitary evolution. All these advantages make present schemes more efficient and more convenient than others in the applications in quantum communication.     

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.     

利用交叉克尔效应制备六光子纠缠态

利用弱非线性的交叉克尔介质和对强相干探测场的动量积分零拍探测,呈现了一个关于制备六光子最大纠缠态的方案,如实现制备Dicke态和W态.在本方案中,只要相干探测光场的强度足够大时,对交叉克尔介质的非线性强度要求可以较弱,因而当前实验技术条件上均能满足本方案的要求.考虑到目前实验上实现单光子很是相对困难的,在信号模上仅用弱...     

Splitting Single-Photon Polarization State with Weak Cross–Kerr Nonlinearity

We propose a three-party scheme for quantum information splitting(QIS) of an arbitrary single-photon polarization state based on weak cross-Kerr nonlinearity combined with linear optics elements such as polarization beam splitters(PBSs) and half wave plates(HWPs). The scheme is generalized to the arbitrary-party case. With the help of quantum nondemolition(QND) measurements, our schemes can be accomplished in an almost deterministic way. The two schemes are feasible with the current technology.     

Control of light in a quantized four level graphene atomic system via self and cross-Kerr nonlinearity

We investigate self and cross-Kerr nonlinearity in a four level quantized graphene atomic medium. The absorption, dispersion, transmission and subluminal/superluminal behaviors of a probe light field are studied. An amplification of the probe light field is observed in the absorption spectrum. The normal and anomalous slope of dispersion is also investigated at the positive/negative absorption region. It is shown that Kerr nonlinearity invert and enhance the subluminal/superluminal behaviors of the pulse and self-Kerr effect is found to be more subluminal/superluminal as compared to cross-Kerr effect. The results show significant applications in information storage, self and cross phase modulation and lasing without inversion.