Quantum Correlation And Interference Based On Four-wave Mixing Process

Quantum optics is one of the most important subjects in modern physics.Quantum correlation,a valuable nonclassical effect,has fundamental scientific significance to quantum optics.Quantum correlated beams can significantly improve the performance of systems due to its reduction of quantum noise.Therefore,quantum correlated beams are widely used in quantum communication and quantum metrology.Recently,the four-wave mixing?FWM?process has been proved to be an effective way to generate quantum correlated beams.This FWM process has many advantages in generating quantum correlated beams.First of all,the quantum correlated beams generated by FWM process can be well separated in the spatial domain due to the spatial multimode nature of FWM process.Secondly,due to the strong nonlinearity of FWM process,this process does not need an optical cavity.Thirdly,this FWM process is proved to be a low-noise amplifier which is close to the quantum limit.Therefore,based on these advantages,FWM process is widely used to generate strong quantum correlation and build optical interferometers.In this thesis,we mainly introduce the quantum correlated beams generated by FWM process and the optical interferometers constructed by the beams generated by FWM process.This thesis will introduce in details as following:1.We utilize the interference to enhance the quantum squeezing between two beams in the continuous variable quantum system.By using the interference,we can enhance the intensity-difference squeezing of two beams generated by phase-insensitive FWM from 8.97±0.24 dB or 8.76±0.26 dB to 10.13±0.21 dB.This is the first time that the intensity-difference squeezing of FWM process exceeds10 dB.Moreover,we also study the effects of the system parameters?the system gain,the intensity ratio of the two input beams and the phase of phase-sensitive amplifier?on the quantum squeezing enhancement.Our experimental results are consistent with the theory.Our work is an effective way to enhance quantum squeezing.Therefore,it is expected to have potential applications in improving the precision of quantum metrology.2.We experimentally demonstrate the phase manipulation of entangled state based on a phase-sensitive amplifier?PSA?.When we lock the phase of the PSA at 0,the type of quadrature entanglement is amplitude-quadrature-difference and phase-quadrature-sum entanglement.On the contrary,when we lock the phase of the PSA at?,the type of quadrature entanglement is the amplitude-quadrature-sum and phase-quadrature-difference entanglement.Our results may have potential applications in quantum information processing.3.I have experimentally generated 10 quantum correlated beams by using cascaded FWM.The intensity-difference squeezing of 10 quantum correlated beams is 6.7±0.3 dB.Moreover,I study the influence of the angle between two pump beams on the number of quantum correlated beams generated from cascade FWM.I find that both the number of the output quantum correlated beams and their degree of quantum correlation from the cascade FWM will increase with the decrease of the angle between the two pump beams.Our cascade FWM system is compact,controllable,and easy to obtain a larger number of quantum correlated beams.The quantum correlated beams generated by our system show strong quantum correlation and can be well separated in the spatial domain.Therefore,our system may find potential applications in quantum information and quantum metrology.4.I have experimentally proved that the phase sensitivity of the bright-seeded SU?1,1?interferometer is better than classical interferometer,and can break the shot noise limit.The experimental results show that the phase sensitivity of the bright-seeded SU?1,1?interferometer can exceed the corresponding shot noise limit for 1.15±0.16 dB.My work may have potential applications in quantum metrology.In addition,I have experimentally constructed a hybrid interferometer by using degenerate FWM.I study the influence of system parameters(the gain of system,one-photon detuning and the temperature of ⁸⁵Rb vapor cell)on the visibility of the interferometer.I find that the visibility of the hybrid interferometer can be above 90%in broad ranges of system parameters.