Multi-colour entanglement directly generated by the enhanced Raman scattering

Multi-colour continuous-variable frequency comb entanglement can be directly generated by enhanced Raman scattering in a hexagonally-poled LiTaO₃ optical superlattice. Raman scattering signals are distinctly boosted by a coupled quasi-phase-matching optical parametric amplification process which has been realized in a previous experiment (Xu et al 2005 Phys. Rev . B 72 064307). The conversion dynamics of the coupled optical parametric amplification process is investigated here using quantum stochastic methodology, and the nature of entanglement among the Raman signals is discussed by applying a necessary and sufficient continuous variable criterion. Multi-colour entanglement with the same frequency interval can be obtained directly, with no optical oscillator cavity, in the enhanced Raman scattering process; this has potential application in quantum communication and computation networks. (letter)