Optical realization of optimal symmetric real state quantum cloning machine

We present an experimentally uniform linear optical scheme to implement the optimal 1→2 symmetric and optimal 1→3 symmetric economical real state quantum cloning machine of the polarization state of the single photon. This scheme requires single-photon sources and two-photon polarization entangled state as input states. It also involves linear optical elements and three-photon coincidence. Then we consider the realistic realization of the scheme by using the parametric down-conversion as photon resources. It is shown that under certain condition, the scheme is feasible by current experimental technology.     

A Four-Dimensional Measurement Scheme for Single Photon Time-Polarization

We propose an experimental scheme to realize the four-dimensional projective measurements tor a single photon. The photon polarization and time-energy provide the four-dimensional Hilbert space. Based on this scheme, we suggest an experiment to test the violation of Bell inequalities of four-dimensional systems. In addition, by virtue of a maximally entangled biphoton state, we also show that it is possible to construct a quantum key distribution channel that can provide two-bit key with one pair of entangled photons.     

Random delayed-choice quantum eraser via two-photon imaging

We report on a delayed-choice quantum eraser experiment based on a two-photon imaging scheme using entangled photon pairs. After the detection of a photon which passed through a double-slit, a random delayed choice is made to erase or not erase the which-path information by the measurement of its distant entangled twin; the particle-like and wave-like behavior of the photon are then recorded simultaneously and respectively by only one set of joint detection devices. The present eraser takes advantage of two-photon imaging. The complete which-path information of a photon is transferred to its distant entangled twin through a “ghost" image. The choice is made on the Fourier transform plane of the ghost image between reading “complete information" or “partial information" of the double-path.     

Linear Optical Protocol for Generation of Greenberger-Horne-Zeilinger State within a Network

We propose a linear optical protocol to generate Greenberger-Horne-Zeilinger (GHZ) state under control of a number of controllers in terms of optical elements. The proposed setup involves simple linear optical elements, (N−1)-photon polarization entangled state, and conventional photon detectors. We show that the protocol can be successfully realized with a certain probability.     

Deterministic generation of entangled photons by cavity-assisted interactions through adiabatic passage

We propose a deterministic scheme for generation of highly entangled photon states using a high-Q two-mode optical cavity and the dark state evolution. Because of the adiabatic operation, our proposal is robust to ambient noise, and the relevant dynamics is insensitive to the randomness of moderate fluctuations regarding experimental parameters. Our scheme not only works deterministically, but also has the advantage of achieving highly entangled photons by adiabatically increasing or decreasing the Rabi frequencies regarding the classical driving pulses, which would be practical in real implementation. Our scheme can also be extended to generation of multiphoton entanglement.     

Spin-orbit hybrid entanglement quantum key distribution scheme

We propose a novel quantum key distribution scheme by using the SAM-OAM hybrid entangled state as the physical resource.To obtain this state,the polarization entangled photon pairs are created by the spontaneous parametric down conversion process,and then,the q-plate acts as a SAM-to-OAM transverter to transform the polarization entangled pairs into the hybrid entangled pattern,which opens the possibility to exploit the features of the higher-dimensional space of OAM state to encode information.In the manipulation and encoding process,Alice performs the SAM measurement by modulating the polarization stateπ lθx on one photon,whereas Bob modulates the OAM sector state lx' on the other photon to encode his key elements using the designed holograms which is implemented by the computer-controlled SLM.With coincidence measurement,Alice could extract the key information.It is showed that N-based keys can be encoded with each pair of entangled photon,and this scheme is robust against Eve’s individual attack.Also,the MUBs are not used.Alice and Bob do not need the classical communication for the key recovery.     

Quantum Computation and Entangled-State Generation Through Photon Emission and Absorption Processes in Separated Cavities

We propose a scheme to implement a two-bit conditional quantum phase gate and generate a multi-atom cluster state and a two-atom three-dimensional entangled state based on photon emission and absorption processes. In the scheme, a Λ-type atom and a V-type atom are individually trapped in two spatially separated cavities connected by an optical fiber. By choosing the interaction time and the ratio of coupling parameters appropriately, the gate operation and entanglement generation can be determinately achieved. We also discuss the influence of photon Leakage on the fidelities of the gate and entanglement and show that the scheme is scalable and feasible in the experimental realization and further utilization.     

Hyperconcentration Based on Projection Measurements

We propose an efficient hyperconcentration protocol for distilling maximally hyperentangled state from partially entangled pure state, resorting to the projection measurement on an auxiliary photon. In our scheme, two photons simultaneously entangled in polarization states and spatial modes are considered. One party performs quantum nondemolition detections on his photon and an additional photon to produce three photon hyperentangled state, then he projects the assistant photon into an orthogonal basis composed of both the polarization and spatial degree of freedom. Then the state of the left two photons collapses into maximally hyperentangled state with a certain probability. In the rest cases, some less-entangled states are obtained, which can be used as resource for the next round concentration. By repeating the concentration process for several rounds, a higher success probability can be obtained, which makes our scheme useful in practical quantum information applications.     

Entanglement formation and violation of Bell's inequality with a semiconductor single photon source

We report the generation of polarization-entangled photons, using a quantum dot single photon source, linear optics, and photodetectors. Two photons created independently are observed to violate Bell's inequality. The density matrix describing the polarization state of the postselected photon pairs is reconstructed and agrees well with a simple model predicting the quality of entanglement from the known parameters of the single photon source. Our scheme provides a method to create no more than one entangled photon pair per cycle after postselection, a feature useful to enhance quantum cryptography protocols based on shared entanglement.     

Linear optical scheme for entanglement concentration of two partially entangled three-photon ${\sf W}$ states

We propose a practical scheme for concentrating entanglement in a pair of unknown partially entangled three-photon W states with only linear optics and photon detectors. In the scheme, Alice, Bob, and Charlie at three distant parties can obtain one maximally entangled three-photon W state with a certain success probability from two identical partially entangled three-photon W states by local operations and classical communication. The proposed setup is very simple, which greatly simplifies the experimental realization of the scheme.     

Four-dimensional entangled state generation in remote cavities

We propose a scheme to generate a maximally four-dimensional entangled state of two six-level atoms in two remote cavities. By choosing suitable intensities and detunings of fields, atomic spontaneous radiation and photon leakage out of cavity and fibre are efficiently suppressed. Thus, the intended state can be generated with high fidelity in the presence of decoherence. We extend the scheme to generate an N-atom four-dimensional entangled state.     

An investigation of the entangled photon walk-off compensation generated by a fiber ring resonator

We firstly present an experimental investigation of the entangled photon states’ recovery using a fiber optic ring resonator incorporating an erbium-doped fiber amplifier (EDFA). The weak light entangled photons can be recovered in both amplitude and states after the optical pumping and polarization control parts are used in the system. A new experimental result of the investigation of thermal effects on the entangled states’ walk-off and compensations has shown that the entangled photon walk-off compensation is achieved by using a pair of polarization control devices. The relationship between thermal effects and the entangled states’ phase shift is investigated and discussed. The walk-off compensation due to temperature changes from 30 to 80 °C is achieved. This shows that the changes in phase of the entangled photons can be negligible when the compensation is employed.     

Quasideterministic generation of entangled atoms in a cavity

We present a scheme to generate a maximally entangled state of two three-level atoms in a cavity. The success or failure of the generation of the desired entangled state can be determined by detecting the polarization of the photon leaking out of the cavity. With the use of an automatic feedback, the success probability of the scheme can be made to approach unity.     

Modified nonclassical coherent state: Squeezing,antibunching, sub-Poissonian photon statistics,realization scheme with the χ<Superscript>(2)</Superscript>-nonlinearity,and generation of a macroscopic entangled state

The nonlinear χ⁽²⁾ Mach-Zehnder interferometer is proposed as a device for conditional generation of a modified coherent nonclassical state. We show that the generated macroscopic state exhibits nonclassical effects, such as squeezing, photon antibunching, and sub-Poissonian statistics. The modified coherent state generates a macroscopic entangled state. The scheme works without the photon number resolving detection but requires high-efficiency photodetectors. We explain the mechanism of generation of the modified coherent non-classical state. The text was submitted by the author in English.     

Entangled photon states generation and regeneration using a nonlinear fiber ring resonator

We propose a simple system of the entangled photon states generation and regeneration using a standard diode laser, a Mach Zehnder Interferometer (MZI) and a fiber optic ring resonator (FORR). Light from the diode laser is launched into an MZI and circulated in the FOOR, without any optical pumping components included in the system. The nonlinear light pulses are generated by a Kerr nonlinear effects type, while the resonance peaks are formed by the four-wave mixing of light pulses in the FORR. The entangled photons can be performed by using the polarization control device, and then detected by the avalanche photo-detectors, where the entangled photon visibility is plotted and seen. Similarly, the entangled photon states can be easily formed by using the appropriated coupling ratios into a fiber coupler, then into a ring resonator, i.e. without an MZI. The use of the entangled photons generation based on a fiber optic scheme for quantum teleportation, quantum key distribution via optical wireless link, and the system of the entangled photon states recovery by using a fiber ring resonator incorporating an erbium-doped fiber (EDF) have been investigated and discussed. The feasibility of dense coding using multi-entangled photons generation based on the fiber optic scheme and the effect of the entangled state walk-off along the optical fiber are also discussed, respectively.     

Remote state preparation of a photonic quantum state via quantum teleportation

We demonstrate an experimental realization of remote state preparation via the quantum teleportation algorithm, using an entangled photon pair in the polarization degree of freedom as the quantum resource. The input state is encoded on the path of one of the photons from the pair. The improved experimental scheme allows us to control the preparation and teleportation of a state over the entire Bloch sphere with a resolution of the degree of mixture given by the coherence length of the photon pair. Both the preparation of the input state and the implementation of the quantum gates are performed in a pair of chained displaced Sagnac interferometers, which contribute to the overall robustness of the setup. An average fidelity above 0.9 is obtained for the remote state preparation process. This scheme allows for a prepared state to be transmitted on every repetition of the experiment, thus giving an intrinsic success probability of 1.     

单光子纠缠态并发度的直接测量

通过分析光学分束器对单光子态的作用关系,提出了一个利用分束器和光子数探测器的单光子纠缠的直接测量方案.方案中用到单光子与空间模纠缠及其两个备份,并让它们通过一个50:50的分束器.选用并发度为纠缠度量,其可由单光子探测器的探测概率直接获得.此方案不需复杂的量子态层析方法,同时只用到在量子信息处理中常用的光学器件,增强了方案在实验上实现的可行性.     

Establishment of Entanglement for Two Atoms Trapped in Two Distant Bad Cavities

A scheme is presented for generation of entangled states for two atoms trapped in two distant bad cavities. The scheme can work with bad cavities with the coupling strength smaller than the cavity decay rate, which is important from the viewpoint of experiment. In the scheme the atoms have no probability of being populated in the excited state and thus the atomic spontaneous emission is suppressed, which increases the probability of success. The fidelity of the entangled state is not affected by the detection eflciency. Furthermore, the scheme does not require the detection of the left-polarized photon and right-polarized photon at the same time.     

通过原子与腔场共振相互作用制备三原子的W态

提出了一种简单、可行的三原子W态制备方案，它是基于三个二能级原子与一个单模腔场共振相互作用实现的。通过控制原子与腔场相互作用时间和耦合参数，无需对腔场态的探测，就可获得三原子的W态。此外，讨论了在现有实验技术下本方案实现的可能性。     

Generation of a χ-type four-atom entangled state

This paper proposes a scheme to generate a new χ-type four-atom entangled state for the first time by using linear optics elements, four one-sided cavities (one three-level atom) and a conventional photon detector. The linear optical elements and conventional photon detector are simple and accessible in experiments, which makes the scheme more feasible with current technology. In addition, the state |χ⁰⁰₃₂₁₄ with probability 1 can be generated as long as there is no photon loss.