Experimental realization of a four-photon seven-qubit graph state for one-way quantum computation.

We propose and demonstrate the scaling up of photonic graph states through path qubit fusion. Two path qubits from separate two-photon four-qubit states are fused to generate a two-dimensional seven-qubit graph state composed of polarization and path qubits. Genuine seven-qubit entanglement is verified by evaluating the witness operator. Six qubits from the graph state are used to demonstrate the Deutsch-Jozsa algorithm for general two-bit functions with a success probability greater than 90%.

Measurement of the entanglement between photonic spatial modes in optical fibers.

We experimentally demonstrate the entanglement of spatial modes between two photons propagating through separate few-mode optical fibers. Quantum states over the two lowest-order spatial modes are measured with highly efficient spatial-mode analyzers based on acousto-optics. Quantum state tomography verifies the entanglement of the spatial-domain Bell state.

Remote preparation of complex spatial states of single photons and verification by two-photon coincidence experiment.

We propose and provide experimental evidence in support of a theory for the remote preparation of a complex spatial state of a single photon. An entangled two-photon source was obtained by spontaneous parametric down-conversion, and a double slit was placed in the path of the signal photon as a scattering object. The signal photon was detected after proper spatial filtering so that the idler photon was prepared in the corresponding single-photon state. By using a two-photon coincidence measurement, we obtained the Radon transform, at several longitudinal distances, of the single-photon Wigner distribution function modified by the double slit. The experimental results are consistent with the idler photon being in a pure state. An inverse Radon transformation can, in principle, be applied to the measured data to reconstruct the modified single-photon Wigner function, which is a complete representation of the amplitude and phase structure of the scattering object.