Complete Distributed Hyper-Entangled-Bell-State Analysis and Quantum Super Dense Coding

We propose a protocol to implement the distributed hyper-entangled-Bell-state analysis (HBSA) for photonic qubits with weak cross-Kerr nonlinearities, QND photon-number-resolving detection, and some linear optical elements. The distinct feature of our scheme is that the BSA for two different degrees of freedom can be implemented deterministically and nondestructively. Based on the present HBSA, we achieve quantum super dense coding with double information capacity, which makes our scheme more significant for long-distance quantum communication.     

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.     

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.     

基于弱非线性实现非破坏性测量两光子Bell态及三光子Greenberger-Horne-Zeilinger态

基于弱非线性及线性光学元件提出非破坏性测量两光子Bell态及三光子 Greenberger-Horne-Zeilinger (GHZ)态方案. 方案中, 首先应用光束分束器及交叉克尔非线性介质对两光子Bell态进行对称性分析, 进而结合控制非门提出三光子分析方案实现对八个三光子GHZ态完全且非破坏性区分. 关键词： Bell态测量 Greenberger-Horne-Zeilinger态测量 弱非线性 量子非破坏性测量     

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.     

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.     

Quantum non-demolition measurement of photon number using weak nonlinearities

We propose an alternative method for the quantum non-demolition measurement of photon numbers wherein weak cross-Kerr nonlinearities are to be used. The usual approach to quantum non-demolition measurements of quantum number involves encoding the photon number, through a cross-Kerr interaction, into a phase shift of a probe coherent state which is then detected through balanced homodyning. Weak nonlinearities produce small phase shifts which are difficult to detect and distinguish. In the method we propose, unbalanced homodyning acts as a displacement operator on the probe beam coherent state such that the cross-Kerr interaction encodes the photon number into the amplitude of a new coherent state. The value of the photon number can be determined by inefficient photon counting on the new coherent state. Our proposed method requires fewer resources than does the usual approach.     

Direct measurement of the concurrence of hybrid entangled state based on parity check measurements

The hybrid entangled state is widely discussed in quantum information processing. In this paper, we propose the first protocol to directly measure the concurrence of the hybrid entangled state. To complete the measurement, we design parity check measurements(PCMs) for both the single polarization qubit and the coherent state. In this protocol, we perform three rounds of PCMs. The results show that we can convert the concurrence into the success probability of picking up the correct states from the initial entangled states. This protocol only uses polarization beam splitters, beam splitters, and weak cross-Kerr nonlinearities, which is feasible for future experiments. This protocol may be useful in future quantum information processing.     

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.     

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.     

Universal quantum computation using all-optical hybrid encoding

By employing displacement operations, single-photon subtractions, and weak cross-Kerr nonlinearity, we propose an alternative way of implementing several universal quantum logical gates for all-optical hybrid qubits encoded in both single-photon polarization state and coherent state. Since these schemes can be straightforwardly implemented only using local operations without teleportation procedure, therefore, less physical resources and simpler operations are required than the existing schemes. With the help of displacement operations, a large phase shift of the coherent state can be obtained via currently available tiny cross-Kerr nonlinearity. Thus, all of these schemes are nearly deterministic and feasible under current technology conditions, which makes them suitable for large-scale quantum computing.     

Near-deterministic efficient all-optical quantum computation

We propose a flexible scheme to prepare various kinds of useful entangled coherent states using weak cross-Kerr nonlinearities and strong laser fields. We then show that, with such entangled states as off-line resources, near-deterministic quantum gates needed for coherent-state-based quantum computation can be efficiently implemented by means of in-line linear-optics elements.     

Remote Quantum Information Concentration Via Weak Cross-Kerr Nonlinearity

By utilizing the quantum parity-check detectors (PCDs) based on the weak cross-Kerr nonlinearities, we propose a scheme for realizing the remote quantum information concentration (RQIC) with the quantum channel of four-photon bound entangled state. After the PCDs and single-photon operations, quantum information initially distributed in three spatially separated photons is concentrated back to a single photon without performing any global operations. The success probability of the scheme is almost a unit. The necessary single-photon unitary operations corresponding to possible measurement outcomes are given detailedly.     

Generation of Four-Photon Cluster State with Coherent Light via Cross-Kerr Nonlinearity

We propose two schemes for preparing four-photon cluster state through cross-Kerr nonlinearity. Two coherent fields interact when they enter a nonlinear Kerr medium. If the interaction time is chosen appropriately in each Kerr medium, four-photon cluster state can be generated based on the results of two homodyne detectors in the first scheme. These schemes only use Kerr medium and homodyne measurements on coherent light fields, which can be efficiently made in quantum optical laboratories. In addition, weak cross-Kerr nonlinearity is sufficient. All of the properties make these schemes feasible in experiments.     

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.     

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.     

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.     

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.     

Teleportation of a Photonic Qubit with Non-maximally Entangled State by Using Weak Cross-Kerr Nonlinearities

We present a scheme for teleporting an unknown single-photon polarization state by using the partially entangled state as the quantum channel. Based on weak cross-Kerr nonlinearity, in this scheme the sender utilizes the quantum parity-check detector (PCD) instead of the usual Bell state measurement. After getting the sender’s measurement result, the receiver of the scheme exploits another PCD to retrieve the original state with some additional photons being introduced. We work out the success probability of the scheme and show that the scheme is feasible with the current technology.