Generation Of Continuous Variable 1.5 ?m Quantum Entangled States And Its Application In Quantum Communication

Continuous variable?CV?non-classical optical field?such as squeezed light,quantum entanglement?is a fundamental resource for quantum information processing and quantum communication.The non-classical states of light at the telecommunication wavelength could be transmitted with low de-coherence characteristic in telecommunication due to its transmission at the lowest optical loss in fiber.And it can be applied to the commercial fiber communication system,which develops practical quantum communication.CV quantum communication over fiber channels has attracted much interest in recent years due to potential improvement of the channel capacity.The quantum nodes distance is limited due to the noise of communication channel loss and extra noise.Quantum repeaters are effective systems to connect multiple communication nodes and the long-distance quantum communication is realized.For example,the use of CV quantum entanglement swapping offers the possibility to improve quantum communication distance,entanglement purification can be used to resist the decoherence effect in quantum teleportation,and the quantum state which matched with the atomic absorption line can be used to realize the quantum storage between the communication nodes.A CV non-classical optical field including squeezed light,quantum entanglement at 1.5?m was experimentally generated by means of optical parametric process in my work.A bright amplitude squeezed light at 780 nm that is the D2 line of rubidium atom was generated from a frequency double with a periodically poled lithium niobate crystal?PPLN?.The distribution of the generated CV quantum entanglement at the telecommunication wavelength of 1550 nm over single mode fibers was experimented.The research about entanglement swapping in fiber channel was studied.The thesis laid the foundation for long distance quantum communication based on optical fiber channel.The main work are as followed:?1?CV squeezed vacuum at 1.5?m was experimentally generated by means of DOPO with a type-I periodically poled KTiOPO₄?PPKTP?crystal.A 6.8 dB squeezed vacuum at 1.5?m was generated.The classical and quantum characteristics of DOPAs are observed experimentally and analysed theoretically.A theoretical model of DOPAs including the extra phase noise caused by the effect of acoustic guided wave brillouin scattering?GAWBS?within the nonlinear crystal is used to explain the degradation of squeezing degree of generated squeezed state.A bright amplitude squeezed light at 780nm was generated from a frequency double with a PPLN.?2?CV quantum entanglement at a telecommunication wavelength of1.5?m using a single NOPA with a type-? PPKTP crystal was generated.By controlling the PPKTP temperature using an excellent home-made temperature controller and fine-tilting the orientation of the PPKTP crystal,a triply resonant OPO was realised.A bright quantum entanglement with anticorrelated amplitude and correlated phase was observed from a NOPA with an injected signal operating at deamplification.EPR-entangled beams with quantum correlations of 8.44 dB and 8.30 dB for both the amplitude and phase quadratures were experimentally generated.?3?CV quantum entanglement distribution was realized at 1.5?m over single mode fiber.When beam b and LO are distributed to Bob over 20 km of single mode fiber,the measured correlation variances of amplitude sum and phase difference are 1.66 and 1.35 dB below the corresponding SNL.The depolarized GAWBS and the excess noise in a single mode fiber is theoretically analyzed and the theoretical prediction is in good agreement with the experimental results.?4?Using two sets of EPR beams and the direct measurement of the Bell-state,the unconditional entanglement swapping for continuous variables is experimentally demonstrated.The quantum correlation degrees of 4.03 dB and3.86 dB below the shot noise limit for the amplitude and phase quadratures are measured straightly between two modes which never directly interact after the entanglement swapping is achievedThe creative works are as follows:?1?A CV squeezed vacuum at 1.5?m and a bright amplitude squeezed light at 780 nm were experimentally generated,respectively.?2?Einstein-Podolsky-Rosen?EPR?-entangled beams at 1.5?m with quantum correlations of 8.3 dB for both the amplitude and phase quadratures are experimentally generated.?3?The distribution of CV quantum entanglement at a telecommunication wavelength over 20 km single mode fiber are realized.?4?The unconditional quantum entanglement swapping based on CV quantum entanglement at a telecommunication wavelength has been experimentally realized.