Demonstration of Local Expansion Toward Large-Scale Entangled Webs
Toshiyuki Tashima, Tsuyoshi Kitano, Şahin Kaya Özdemir, Takashi Yamamoto, Masato Koashi, Nobuyuki Imoto · Physical Review Letters · 2010
We demonstrate an optical gate that increases the size of polarization-based W states by accessing only one of the qubits. Using this gate, we have generated three-photon and four-photon W states with fidelities 0.836 ± 0.042 and 0.784 ± 0.028, respectively. We also confirmed the existence of pairwise entanglement in every pair of qubits, including the one that was left untouched by the gate. The gate is applicable to any size of W states and hence is a universal tool for expanding entanglement.