The Experimental Realization And Application Of Intensity Difference Squeezing Based On Four-wave Mixing In Atomic System

Due to the noise level of squeezed state could break through the low boundary set by classical waves, which is called standard quantum limit (SQL) or shot noise level (SNL), squeezed state has been one of the important and hot research topics in quantum optics. Squeezed lights show great applications in detection and transportation of superdim signal as well as precision measurement of signal which requires high signal to noise ratio (SNR) device. In the meantime, using squeezed lights to generate and control entangled states is the basis in quantum information science and one of the fundamental tools in quantum communication and quantum measurement. Squeezed lights have been bringing the optics science great revolution that cannot be realized by classical lights. It is making the transmission of the signal safer as well as a bigger storage capacity and faster processing of the signal in the quantum world.The interaction between lights and atoms could result in a bunch of interesting physical phenomenon like electromagnetically induced transparency (EIT)、Raman process and four-wave mixing. This makes the atoms good candidate for the generation、storage and retrieval of optical information. In this thesis, we describe a four-wave mixing process takes place in hot Rb-85vapor, which is realized by injecting a vapor cell with a strong pump beam and a weak probe beam, after which a conjugate beam that demonstrates strong relative intensity correlation with the amplified probe beam is generated. In our experiment we successfully achieve5dB intensity difference.Low frequency squeezing and squeezing bandwidth are also important characteristics of squeezed lights since they are relevant to how to detect and transmit a signal of certain bandwidth during signal processing. Low frequency squeezing could be of great assistance in detecting the weak information in low frequency region, such as the gravitational wave detection. We obtain an intensity difference squeezing down to1.5kHz. We also found that by changing the power of the pump beam, the squeezing bandwidth could be flexibly controlled and adjusted, which is a potential application in the bandwidth selection of quantum lights in quantum communication. By utililizing two cascaded four-wave mixing processes as the nonlinear parametric amplifiers and nonlinear beam-splitters instead of classical beam-splitters in traditional linear M-Z interferometer (LI), we first experimentally construct a nonlinear interferometer (NLI) which is proposed by B. Yurke in1986. Because of the nonlinear amplification of the intensity of the signal, the NLI has stronger interference fringe intensity than traditional LI and therefore able to measure a smaller phase shift of the phase sensing field inside the interferometer. Also when destructively interfered, the quantum correlation of the probe and conjugate could in principle make the noise of the output of the NLI touch the SNL, or very closed with loss inside the interferometer. We obtain a stronger SNR with NLI compared with LI when the intensities of the sensing fields are the same.