Toshiyuki Tashima

Local transformation of two einstein-podolsky-rosen photon pairs into a three-photon w state.

We propose and experimentally demonstrate a transformation of two Einstein-Podolsky-Rosen photon pairs distributed among three parties into a three-photon W state using local operations and classical communication. We then characterize the final state using quantum state tomography on the three-photon state and on its marginal bipartite states. The fidelity of the final state to the ideal W state is 0.778+/-0.043 and the expectation value for its witness operator is -0.111+/-0.043 implying the success of the proposed local transformation.

Tapered fiber coupling of single photons emitted by a deterministically positioned single nitrogen vacancy center

A diamond nano-crystal hosting a single nitrogen vacancy (NV) center is optically selected with a confocal scanning microscope and positioned deterministically onto the subwavelength-diameter waist of a tapered optical fiber (TOF) with the help of an atomic force microscope. Based on this nano-manipulation technique, we experimentally demonstrate the evanescent coupling of single fluorescence photons emitted by a single NV-center to the guided mode of the TOF. By comparing photon count rates of the fiber-guided and the free-space modes and with the help of numerical finite-difference time domain simulations, we determine a lower and upper bound for the coupling efficiency of (9.5 ± 0.6)% and (10.4 ± 0.7)%, respectively. Our results are a promising starting point for future integration of single photon sources into photonic quantum networks and applications in quantum information science.

Local expansion of photonic W state using a polarization-dependent beamsplitter

We propose a simple probabilistic optical gate to expand polarization entangled W states. The gate uses one polarization-dependent beamsplitter and a horizontally polarized single photon as an ancilla. The gate post-selectively expands N-photon W states to (N+1)-photon W states. A feasibility analysis considering the realistic experimental conditions shows that the scheme is within the reach of the current quantum optical technologies.

An elementary optical gate for expanding entanglement web

We introduce an elementary optical gate for expanding polarization entangled W states, in which every pair of photons are entangled alike. The gate is composed of a pair of 50:50 beamsplitters and ancillary photons in the two-photon Fock state. By seeding one of the photons in an

Perfect selective alignment of nitrogen-vacancy centers in diamond

n

Demonstration of local expansion toward large-scale entangled webs.

-photon W state into this gate, we obtain an

Optimal local expansion ofWstates using linear optics and Fock states

(n+2)

Efficient decoherence-free entanglement distribution over lossy quantum channels.

-photon W state after post-selection. This gate gives a better efficiency and a simpler implementation than previous proposals for

Experimental characterization of a non-local convertor for quantum photonic networks

\rm W

Optically detected magnetic resonance of high-density ensemble of NV(-) centers in diamond.

-state preparation.