Experiental studies on quantum measurements using entanglement

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We experimentally investigate the temporal characteristics of picosecond squeezed pulses generated via an optical parametric amplification in a periodically poled MgO:LiNbO_3 waveguide. The noise variances for the various time delays between the squeezed pulse and a local oscillator are measured using a balanced homodyne detector. The measured delay dependence is asymmetric, and this asymmetry indicates that the phase chirping of the squeezed pulse is different from that of the local oscillator pulse. We show that the observed squeezing can be improved by using the pulse shaping of the local oscillator. By using a temporally shaped local oscillator in a balanced homodyne detection, we obverved the squeezing of -5.0 dB below the shot noise level. To our best knowledge, this is the highest level obtained for waveguide squeezers.