Simple experimental scheme of preparing a four-photon entangled state for the teleportation-based realization of a linear optical controlled-NOT gate

We propose a simple experimental scheme of preparing a four-photon entangled state, which is a useful resource for two-qubit quantum operations, e.g., the controlled-NOT gate. The scheme can successfully postselect the events of the desired four-photon entangled state in the coincidence basis and can be constructed with four photons from parametric down conversion, linear optical devices, and conventional photon detectors, all of which are available in current technology. We also show an experimental scheme for a controlled-NOT gate based on teleportation with the prepared four-photon state.

Figure 1

Schematic diagram of preparing a four-photon polarization entangled state $\mid \chi ⟩$.

Figure 2

Schematic diagram of a teleportation-based controlled-NOT gate. $\mid \chi ⟩$ can be produced by using the state preparation method of Sec. 2. The input of the CNOT gate is a product state $(\alpha {\mid H⟩}_5+\beta {\mid V⟩}_5)(\gamma {\mid H⟩}_8+\delta {\mid V⟩}_8)$. This state is prepared by transforming the polarizations of photons 5 and 8. The parts surrounded by dotted lines correspond to Bell measurements.