We experimentally demonstrated that the quantum correlations of amplitude andphase quadratures between signal and idler beams produced from a non-degenerateoptical parametric amplifier (NOPA) can be significantly improved by using amode cleaner in the pump field and reducing the phase fluctuations in phaselocking systems. Based on the two technical improvements the quantumentanglement measured with a two-mode homodyne detector is enhanced from ~ 4 dBto ~ 6 dB below the quantum noise limit using the same NOPA and nonlinearcrystal.
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