Deterministic Controlled-NOT gate for single-photon two-qubit quantum logic

摘要

We demonstrate a robust implementation of a deterministic linear-optical Controlled-NOT (CNOT) gate for single-photon two-qubit quantum logic. A polarization Sagnac interferometer with an embedded 45$^{\circ}$-oriented dove prism is used to enable the polarization control qubit to act on the momentum (spatial) target qubit of the same photon. The CNOT gate requires no active stabilization because the two spatial modes share a common path, and it is used to entangle the polarization and momentum qubits. Single-photon two-qubit quantum logic can be applied to hyperentangled photon pairs for generating the Greenberger-Horne-Zeilinger (GHZ) state and demonstrating a nonstatistical violation of the Bell's inequality.