Efficient generation of CV entanglement by triply resonant non-degenerate OPA

摘要

CV entangled CW bright beams are experimentally generated by a Non-degenerate "triply resonant" Optical Parametric Amplifier (NOPA) based on PPKTP type-II crystal below threshold. Operating the OPA at frequency degeneracy makes the down-converted entangled beams able to be optically manipulated for generating different combination of the entangled system. Particular care has been required by the triply resonance condition essential to obtain a suffcient degree of entanglement. The triply resonance condition is pursued by combining temperature phase-matching and crystal tilting in an optical cavity so to optimize the triple resonance condition acting on different independent parameters. Exploiting the dependence of the bipartite system covariance matrix on different combination of this continuous variable two-mode states it can be directly measured using a single homodyne detector and few linear optical elements. The system is actually operating at the University of Napoli-Quantum Optics Laboratory. Preliminary measurements show that CV entanglement is present at the OPO output. This source of CV entanglement can be used for quantum communication purposes. The technical tricks herein implemented are interesting also for realizing triply resonant CW OPOs whose spectral properties and conversion efficiencies are better compared to single and double resonant devices. The quality of entanglement is also improved thanks to the use of a single cavity instead of dual cavities often employed in triply resonant devices. The measurement method can be applied to generic bipartite states made of frequency degenerate but orthogonally polarized modes.