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Underwater imaging is a challenging topic in the field of photography due to the absorption and scattering of light by water, which reduces the imaging distance and visibility. In this paper, the effects of seawater on the quality of ghost imaging (GI) are analyzed theoretically and experimentally. Our results indicate that GI technique, to a certain extent, can achieve better imaging quality than conventional imaging, especially under weak light condition in seawater environments. The compressed sensing ghost imaging (CSGI) can further enhance the visibility of ghost images with fewer measurements. Therefore, ghost imaging has the potential of realizing longer-distance underwater imaging, owing to its robustness against seawater environmental disturbance.

We present schemes for deterministically generating multi-qubit electron-spin entangled cluster states by the giant circular birefringence, induced by the interface between the spin of a photon and the spin of an electron confined in a quantum dot embedded in a double-sided microcavity. Based on this interface, we construct the controlled phase flip (CPF) gate deterministically which is performed on electron-spin qubits and is the essential component of the cluster-state generation. As one of the universal gates, the CPF gate constructed can also be utilized in achieving scalable quantum computing. Besides, we propose the entanglement concentration protocol to reconstruct a partially entangled cluster state into a maximally entangled one, resorting to the projection measurement on an ancillary photon. By iterating the concentration scheme several times, the maximum success probability can be achieved. The fidelities and experimental feasibilities are analyzed with respect to currently available techniques, indicating that our schemes can work well in both the strong and weak (Purcell) coupling regimes.

We propose a simple scheme for generating three-photon polarization-entangled GHZ state via cross-Kerr medium, linear optical elements and P homodyne measurement. In our protocol, the two-photon interference is used rather than the single-photon interference, which decreases the difficulty in experimental realization. Besides, the generation scheme proposed doubles the phase shift θ , which will result in lower error probability and decoherence effect. These advantages make our scheme more feasible in the regime of weak cross-Kerr nonlinearity with current experimental technologies. In addition, we give two efficient schemes for the generation of arbitrary multi-photon GHZ state, which is significant to large-scale quantum information processing (QIP).

We present an explicit protocol for deterministic exact teleportation via two partially entangled pairs of particles. The protocol consists of a local generalized measurement described by a positive operator-valued measure, one-way classical communication, and a corresponding local unitary operation. We find the required generalized measurement, which can experimentally be realized by performing a unitary operation in the extended space and a conventional orthogonal measurement. A simple protocol for deterministic entanglement concentration is also obtained.