Generation of High-Fidelity Four-Photon Cluster State and Quantum-Domain Demonstration of One-Way Quantum Computing

We experimentally demonstrate a simple scheme for generating a four-photon entangled cluster state with fidelity over $0.860\pm 0.015$. We show that the fidelity is high enough to guarantee that the produced state is distinguished from Greenberger-Horne-Zeilinger, $W$, and Dicke types of genuine four-qubit entanglement. We also demonstrate basic operations of one-way quantum computing using the produced state and show that the output state fidelities surpass classical bounds, which indicates that the entanglement in the produced state essentially contributes to the quantum operation.

Figure 1

Experimental setup for preparing $|C_4⟩$.

Figure 2

Experimental setup for preparing two single photons and an entangled photon pair.

Figure 3

Fourfold coincidence probabilities for measurement settings (a) $XXZZ$, (b) $ZZXX$, (c) $YYZZ$, and (d) $ZZYY$. The ideal cases are shown in (a’)–(d’).

Figure 4

Physical implementation and the quantum circuit of a two-qubit gate.

Figure 5

Physical implementation and the quantum circuit of a single-qubit rotation.