Generation and concentration of two-photon partially entangled Knill-Laflamme-Milburn state

摘要

The protocol for the compact generation of the two-photon four-dimensional spatial-mode partially entangled Knill-Laflamme-Milburn (KLM) state is proposed. The two-photon entanglement shared among four spatially distinct optical modes can be generated from three concurrent spontaneous parametric down-conversion processes by using the multiple quasiphase-matching technique. The scheme for the concentration of the two-photon four-dimensional spatial-mode partially entangled KLM state is also proposed. By using quantum non-destructive detection and local operation, the two-photon maximally entangled KLM state can be obtained and used as an entangled quantum channel in quantum communication.