Entanglement contains one of the most interesting features of quantum mechanics, often named quantum non-locality [1,2]. This means entangled states are not separable regardless of the spatial separation of their components. Measurement results on one particle of a two-particle entangled state define the state of the other particle instantaneously with neither particle enjoying its own well-defined state before the measurement.So far experimental confirmation of entanglement has been restricted to qubits, i.e. two-state quantum systems including recent realization of three- [3,4] and four-qubit [5,6] entanglements. Yet, an ever increasing body of theoretical work calls for entanglement in quantum system of higher dimensions [7,8]. For photons one is restricted to qubits as long as the entanglement is realized using the photons polarization. Here we report the first realization of entanglement exploiting the orbital angular momentum of photons,

We report an experiment in which a light pulse is decelerated and trapped in a vapor of Rb atoms, stored for a controlled period of time, and then released on demand. We accomplish this storage of light by dynamically reducing the group velocity of the light pulse to zero, so that the coherent excitation of the light is reversibly mapped into a collective Zeeman (spin) coherence of the Rb vapor.

We report an experimental realization of one-way quantum computing on a two-photon four-qubit cluster state. This is accomplished by developing a two-photon cluster state source entangled both in polarization and spatial modes. With this special source, we implemented a highly efficient Grover's search algorithm and high-fidelity two qubits quantum gates. Our experiment demonstrates that such cluster states could serve as an ideal source and a building block for rapid and precise optical quantum computation.PACS numbers: 03.67. Lx, 03.67.Mn, 42.50.Dv Highly entangled multipartite states, so-called cluster states, have recently raised enormous interest in quantum information processing (QIP). These sorts of states are crucial as a fundamental resource and a building block aimed at one-way universal quantum computing [1]. They are also essential elements for various quantum error correction codes and quantum communication protocols [2]. Moreover, the entanglements are shown to be robust against decoherence [3], and persistent against loss of qubits [1], and thus are exceptionally well suited for quantum computing and many tasks [1,2]. Considerable efforts have been made toward generating and characterizing cluster state in linear optics [4,5,6,7,8,9]. Recently the principal feasibility of a one-way quantum computing model has been experimentally demonstrated through 4-photon cluster states successfully [7,8,10].So far, preparing photonic cluster state still suffers from several serious limitations. Due to the probabilistic nature and Poissonian distribution of the parametric down-conversion process, the generation rate of 4-photon cluster states is quite low [5,6,7,8], and largely restricts speed of computing. Besides, the quality and fidelity of prepared cluster states are relatively low [6,7,8], which are difficult to be improved substantially. These disadvantages consequently impose great challenges of advancement even for few-qubit quantum computing.Fortunately, motivated by the progress that an important type of states termed hyper-entangled states have been experimentally generated [11,12,13,14], we have the possibility to produce a new type of cluster state (2-photon 4-qubit cluster state) with nearly perfect fidelity and high generation rate. The hyper-entangled states have been used to test "All-Versus-Nothing" (AVN) quantum nonlocality [11,12,15], and are shown to lead to an enhancing violation of local realism [16,17]. The states also enable to perform complete deterministic Bell state analysis [18] as demonstrated in [14,19].In this Letter we report an experimental realization of one-way quantum computing with such a 2-photon 4-qubit cluster state. The key idea is to develop and employ a bright source which produces a 2-photon state entangled both in polarization and spatial modes. We are thus able to implement the Grover's algorithm and quantum gates with excellent performances. The genuine four-partite entanglement and high fidelity of better than 88% are characterized by an optimal entanglement w...

Quantum teleportation 1 , a way to transfer the state of a quantum system from one location to another, is central to quantum communication 2 and plays an important role in a number of quantum computation protocols 3-5 . Previous experimental demonstrations have been implemented with photonic 6-8 or ionic qubits 9,10 . Very recently long-distance teleportation 11,12 and open-destination teleportation 13 have also been realized. Until now, previous experiments 6-13 have only been able to teleport single qubits. However, since teleportation of single qubits is insufficient for a large-scale realization of quantum communication and computation 2-5 , teleportation of a composite system containing two or more qubits has been seen as a long-standing goal in quantum information science.Here, we present the experimental realization of quantum teleportation of a two-qubit composite system. In the experiment, we develop and exploit a six-photon interferometer to teleport an arbitrary polarization state of two photons. The observed teleportation fidelities for different initial states are all