THE PROBLEM OF LIGHT DETECTION IN THE PRESENCE OF ZEROPOINT FLUCTUATIONS: A PHYSICAL MODEL FOR THE VISION OF WEAK SIGNALS

We examine the possibility of obtaining a model of human vision within the context of a purely wave theory of light, including the zero-point field. We show that the model meets one of the main objections to this assumption, namely that photodetectors should be activated to saturation by the zeropoint field alone. A straightforward consequence of the model is the existence of a minimal signal intensity which may be discriminated by the human eye from the (huge) zeropoint intensity. The threshold predicted by the model roughly agrees with empirical results.     

外场驱动下腔QED中实现任意两原子态的隐形传送方案

提出了一种外场驱动下在腔QED中实现任意两原子态隐形传送的方案.在隐形传送的过程中.以两原子最大纠缠态作为量子通道,不用考虑腔场耗散和外界热场环境的影响.在传送过程中包含着对原子的Bell基测量,但不需要直接进行Bell基测量,而且最终能成功实现传送的几率为1.0.同时这种方案也可以用来传送未知的三原子GHZ态,传送的几率也为1.0.     

Quantum teleportation across a biological membrane by means of correlated spin pair dynamics in photosynthetic reaction centers

In the process coined quantum teleportation the complete information contained in an input quantum stateΨ _i is teleported to a distant location at which the original quantum state is regenerated as teleported output stateΨ _i. This paper presents the proof-of-feasibility concept of a quantum teleportation experiment during which an arbitrary input quantum state is teleported across a biological membrane. As particular aspect it is emphasized that all essential subprocesses of the usual quantum teleportation scheme are suggested to be realized by free running reaction processes in a biological membrane-bound reaction center complex with only one significant adaptation required at the input side. The first process of generation of a spin-correlated (Einstein-Podolsky-Rosen) pair of particles (Bell-state source) is a naturally occurring process realized in photosynthetic reaction centers by the primary processes of light-induced charge separation across the membrane. The second process is the so-called Bell-state measurement, which is able to store the complete information of the input quantum state. It is suggested to be realized by a fast spin-dependent recombination between one pair partner spin and a properly engineered input spin. Under suitable recombination conditions the remaining second pair partner spin, situated at the receiver location on the other side of the membrane, is shown to end up in the quantum state identical to that of the initial input state due to the fixed spin correlation of the Bell-state source and the particular spin selectivity of the recombination process. Thus, the input (spin) quantum state is teleported from the spin near the (electron charge) donor side to the acceptor side of the membrane-bound photosynthetic reaction center complex. A comprehensive discussion is presented for this quantum teleportation concept using photosynthetic reaction centers as the quantum channel of communication. Standard electron paramagnetic resonance techniques can be used to set up the input state and read out or hand over the output state for subsequent quantum information processing.     

Polarization-momentum hyper-entangled two photon states

We present a parametric source which allows the engineering of polarization-momentum hyperentangled two photon states based on linear optics and a single type-I nonlinear crystal. The nonlocal character of these states has been verified by various tests, including the “All Versus Nothing” test of local realism [A. Cabello, Phys. Rev. Lett. 87, 010403 (2001)], which represents a generalization of the GHZ to the case of two entangled particles and two observers. We have also created a complete and deterministic Bell-state measurement by a novel experimental scheme which adopts polarization-momentum hyper-entanglement and requires linear optics and single photon detectors. The text was submitted by the authors in English.     

Multiparty quantum secret sharing with collective eavesdropping-check

A scalable protocol for multiparty quantum secret splitting with collective eavesdropping-check is proposed by using Einstein-Podolsky-Rosen pairs. We analyze the security of this protocol and prove that it can stand against some possible attacks in an ideal condition. Meanwhile, this protocol utilizes quantum dense coding to achieve a high intrinsic efficiency and source capacity. Moreover, only Bell-state measurement and local unitary operations are required, which makes this protocol more convenient from an applied point of view.     

Teleportation of N-qubit W State without Bell-State Measurement via SelectiveResonant Interaction in Cavity QED

We present a scheme in which the N-atom W state is teleported byemploying the selective interaction of a cavity field with a driventhree-level atom in the λ configuration and detecting a single atom in one of the ground states. The long-lived W state is teleported from atom A to atom B when the atoms B and A are sent through a cavity successively and atom A is then detected. The advantage is that the present one does not involve the Bell-state measurement and is robust against the atomic spontaneous emission.     

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     

Quantum Information Splitting of an Arbitrary Three-Atom State by Using W-class States in Cavity QED

We demonstrate that four sets of W-class states can be used to realize the deterministic quantum information splitting of an arbitrary three-atom state in cavity QED. The scheme does not involve Bell-state measurement and is insensitive to both the cavity decay and the thermal field.     

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.     

Quantum Information Splitting of an Arbitrary Two-Atom State by Using W-Class States in Cavity QED

We demonstrate that three sets of W-class states can be used to realize the deterministic quantum information splitting of an arbitrary two-atom state in cavity QED. The scheme does not involve Bell-state measurement and is not sensitive to both the cavity decay and the thermal field.     

Splitting Quantum Information with Five-Atom Cluster State in Cavity QED

A realizable scheme is proposed for implementing quantum information splitting with five-atom cluster state in cavity QED, where we explicitly illustrate the procedure. The scheme does not involve Bell-state measurement and is insensitive to the cavity and the thermal field.     

Concentration scheme for partially entangled photon states via entanglement reflector and no Bell-state analysis

We propose a protocol to concentrate partially entangled states of photons using entanglement reflector, which consists of a single electron spin confined in a charged quantum dot inside a single-sided microcavity. The outstanding advantage of the proposed scheme is its experimental simplicity and feasibility since it only needs to perform a single local measurement on electronic spins rather than a joint Bell-state measurement on photons. We then extend this scheme to concentrate N-photon Greenberger-Horne-Zeilinger state. Finally, we analyze the influence of various imperfections on the scheme.     

Quantum Information Splitting of an Arbitrary Two-Atom State by Using a Genuinely Entangled Five-Atom State in Cavity QED

We demonstrate that a genuinely entangled five-atom state can be used to realize the deterministic quantum information splitting of an arbitrary two-atom state in cavity QED. The scheme does not involve Bell-state measurement and is insensitive to both the cavity decay and the thermal field. The presented protocol is showed to be secure against certain eavesdropping attacks.     

Teleportation of atomic entangled states with a thermal cavity

We propose a most simple and experimentally feasible scheme for teleporting unknown atomic entangled states in driven cavity quantum electrodynamics (QED). In our scheme, the joint Bell-state measurement (BSM) is not required, and the successful probability can reach 1.0. Furthermore, the scheme is insensitive to the cavity decay and the thermal field.     

非Bell基测量实现任意单原子量子态的隐形传态

在腔QED系统中,我们用一个两原子的Bell态作为量子信道,提出了一个简单的任意单原子的隐形传态方案。在该方案中,通过引入一个辅助原子,可以用单原子的测量来代替Bell基测量,并且成功传送的概率能够达到1。此外,方案不受腔损和热场的影响。     

Efficient multi-party quantum state sharing of an arbitrary two-qubit state

We present an efficient scheme for sharing an arbitrary two-qubit quantum state with n agents. In this scheme, the sender Alice first prepares an n + 2-particle GHZ state and introduces a Controlled-Not (CNOT) gate operation. Then, she utilizes the n + 2-particle entangled state as the quantum resource. After setting up the quantum channel, she performs one Bell-state measurement and another single-particle measurement, rather than two Bell-state measurements. In addition, except that the designated recover of the quantum secret just keeps two particles, almost all agents only hold one particle in their hands respectively, and thus they only need to perform a single-particle measurement on the respective particle with the basis X. Compared with other schemes based on entanglement swapping, our scheme needs less qubits as the quantum resources and exchanges less classical information, and thus obtains higher communication efficiency.     

Quantum information splitting of an arbitrary three-qubit state via the cavity input–output process

We propose a realizable quantum information splitting (QIS) scheme for an arbitrary three-qubit state via the cavity input–output process. In our scheme, a four-qubit cluster state and a three-qubit Greenberger–Horne–Zeilinge (GHZ) state are used as quantum channel. The sender and controller only need to perform Bell-state measurements and a single-qubit measurement, respectively. The receiver can reconstruct the arbitrary three-qubit state by classical communication and local operations. Compared with the scheme in Nie et al. [Optics Communications 284 (2011) 1457], the quantum resources and classical information in our scheme are decreased by 5 qubits and 1 bit, respectively. Moreover, we replace the W-state category measurement in the former with Bell-state measurements and a single-qubit measurement, which is more simple and feasible in experiment.     

Deterministic Remote Entangled State Preparation Using Cluster State in Cavity QED

We propose a scheme to prepare a two-qubit remote entangled state based on four-qubit cluster state in cavity quantum electrodynamics which involves the interaction of the atoms with the cavity. Through using four-particle cluster state as a quantum channel, we shown that the probability and fidelity of the successful remote state preparation can approach unit. In addition, our protocol only need single qubit measurement instead of the conventional Bell-state measurement, then it is quite simple but also very robust to the cavity decay and the influence of the thermal field.     

Scheme for Teleportation of Four-Level Atomic States in Thermal Cavities

We propose a scheme for teleportation of four-level atomic states in thermal cavities. The scheme does not involve the generalized Bell-state or generalized GHZ-state measurement, which is difficult in practice. Another feature of the scheme is that it does not require individual addressing of atoms in cavity and is insensitive to both cavity decay and thermal field, which is of importance in point of experiment.     

Controlled Quantum State Transfer with Separate Measurements in Cavity QED

An experimental scheme on controlled quantum state transfer is proposed in cavity quantum electrodynamics (QED) without joint Bell-state measurement (BSM). A quantum state can be transferred perfectly with the help of the cooperation of the third side by constructing a three-atom GHZ entangled state as the controlled channel. This scheme is insensitive to the cavity decay and the thermal field. The probability of the success in our scheme is 1.0.