Experimental Improvement Of Continuous Variable Entanglement Enhancement

The EPR entangled states of light have been extensively applied in continuous variable (CV) quantum information, such as quantum teleportation, quantum dense coding and entanglement swapping. But for the restriction of crystal and loss of in-cavity, it is very hard to generate the EPR entanglement with enough correlation degrees with only one NOPA. In order to resolve these problems, we theoretically and experimentally investigated the phase-sensitive manipulation and enhancement of EPR entangled states in the NOPA.We theoretically calculated the affection of cavity detuning, in-cavity loses, the transmission rate of input-output mirror, phase fluctuation and extra noise on the continuous variable entanglement enhancement. Then, by using high finesse mode cleaner in the pump and injected filed and improving the accuracy in locking system, we improved the experimental system of continuous variable entanglement enhancement. The initial correlation degrees between amplitude and phase quadratures of EPR entanglement field are improved from 2.4±0.2dB,24±0.2dB to 4.0±0.2dB,3.9±0.2dB, and the quantum entanglement between amplitude and phase quadratures of the output field are improved from 3.0±0.2 dB,3.0±0.2 dB to 5.6±0.2 dB, 5.5±0.2 dB, respectively. With respect to the past system, both the efficient and result of the entanglement enhancement are improved.