Experimental And Theoretical Investigation On Entanglement Enhancement And Manipulation And Generation Of Tunable Entangled Optical Fields

The entangled states of light with amplitude and phase quadrature quantum correlations have been extensively applied in continuous variable (CV) quantum information, such as quantum teleportation, quantum dense coding and entanglement swapping. It is significant to enhance and manipulate quantum entanglement of optical entangled states for realizing high quality information processing and achieving long distance quantum communication. On the other side, in order to realize CV quantum information networks including more nodes, the entangled light must interact with atomic samples and thus the frequency of light should be precisely tuned to resonate with the transition of atomic lines. Besides, the excess classical noises in the seed beams of a non degenerate optical parametric amplifier (NOPA) have significant influence to the entanglement of the output field, so we have to avoid the influence in experiments for obtaining higher entanglement. In this Ph.D thesis, I am going to present the experimental researches about the entanglement enhancement and manipulation by means of a NOPA, then discuss the experimental generation of frequency-tunable entangled optical beams with continuous variables, and lastly describe the influence of excess noises in seed beams of NOPA on continuous-variable entanglement of output field.Main contents are as following: 1. We experimentally demonstrate that the quantum entanglement between amplitude and phase quadratures of optical modes can be enhanced and manipulated phase-sensitively by means of a NOPA. When the NOPA operates at de-amplification, the correlation degree of the output entangled optical fields with quadrature amplitude anti-correlation and quadrature phase correlation are enhanced from 2.4dB to 3.0dB. When the NOPA operates at amplification, the entangled features are changed from quadrature amplitude anti-correlation and quadrature phase correlation to quadrature amplitude correlation and quadrature phase anti-correlation.2. Through controlling the temperature of the nonlinear crystal, frequency tunable continuous-variable entangled optical beams are experimentally prepared with a non-degenerate optical parametric oscillator. The measured correlation variances of amplitude and phase quadratures are 3.2 dB and 1.5dB below the corresponding Shot Noise Level in the tuning range of 2.25nm, respectively.3. The influence of the excess classical noises in the injected seed beams on the entanglement of the output fields generated by a NOPA operating at deamplification was theoretically and experimentally investigated. If increasing the excess classical noises in the seed beams, the correlation degree of the output entangled optical fields, which is scaled by the quantum noise limit, will decreased rapidly. The experimental results are in good agreement with the theoretical calculation.The creative works are as follows:A. We experimentally demonstrated that the CV quantum entanglement of optical fields can be enhanced and manipulated by means of a NOPA.B. The frequency-tunable entangled optical beams were experimentally prepared with a non-degenerate optical parametric oscillator.C. The influence of the excess classical noises in the injected seed beams to CV entanglement of optical beams generated by a NOPA was theoretically and experimentally investigated.