Nonclassical Effects Of The Superposition Of Multi-Coherent States And Their Preparation And Decoherence

The study of the nonclassical states of light has recently attracted renewed attentionof many investigator because of the key role they may play, beyond the traditional realmof quantum optics, in research fields of great current interest, such as laser pulsed atomsand molecules; Bose-Einstein condensation and atom lasers; and quantum informationtheory. It has been demonstrated that nonclassical effects and preparations of quantumstates of light are strongly related to the study of quantum communication and quantumcomputation. In the processes of generation and distribution of quantum keys, such asthe procotols of one photon, the high quality single photon source which emits antibunch-ing photon one by one, is necessary. The squeezing effects of quantum states can makequantum noise lower than the limit of the standard quantum ?uctuations. This will helpto improve signal to noise ratio of weak signal detection. Calculating the Wigner functionis important ways obtaining information in the evolution of the states. Moreover, Non-classicality of the inputs is necessary for entangling field states and is helpful to quantumoptical implementation of quantum information processing.Based on many potential applications of nonclassical effects of quantum states, inthis dissertation, proceeding from the principle of superposition, we construct severalkinds of new quantum states by superpositions of multi-coherent states and discuss indetails their nonclassical effects and their preparation and quantum decoherence. Themain achieved works are as follows:Study effects of the vacuum state on the statistics of nonclassical states. Non-classical properties of adding (substructing) the vacuum state to the superposition of twocoherent statesπ/2 out of phase with each other are discussed, such as Photon numberdistribution, quadrature squeezing, negativity of the Wigner function and phase proba-bility distribution. The results show that depending on the vacuum state coefficient, avariety of classical and nonclassical states that can be used to improve the transmission ofinformation can be generated. The constructed new states can clearly exhibit the differentfeatures of quantum interference distincting from those of the ordinary the superpositionof two coherent states. By superposition coefficients of the vacuum choice, one can findthe maximum squeezing degree of non-classical states and quantum interference of the superposition state.Construction of the elliptical states and their generation. Having motivated thestudy of strong nonclassicality of the circular states, further elliptical states are con-structed. The statistical properties of the states by using the photon-number distribution,sub-poissonian photon statistics, quadrature squeezing, Wigner function are investigated.It is shown that the constructed new states exhibit sub-poissonian photon statistics andinfinite quadrature squeezing. The interference fringes between the coherent states formthe elliptic annuli of Fock states in the Wigner-function picture. Based on the motionof the center of mass of a trapped ion, by unitary evolution and some measuring for up-per electronic state by projecting the ion state vector on |↑, an experimental scheme isproposed for generating equidistant coherent-state superpositions on an ellipse.Study the Pegg-Barnett phase properties of the odd and even elliptical statesand quantum decoherence. By phase operator theory and ways of numerical values ofPegg-Barnett, the phase probability distributions of Schrodinger cat states are calculated,and number operator and phase operator squeezing are discussed. With the increasing ofthe number of coherent states, we found that the Pegg-Barnett phase probability distribu-tion is more sensitive with respect to the character of quantum interference between thedifferent components of the states. Both the even and odd circular states have been shownto exhibit photon-number and phase squeezing. The phase distributions of the ellipticalstates are not longer normalized like the circular states. The elliptical states are the mosteasily to be observed in the direction of the long axle of the elliptical states.Construction of the nonlinear elliptical states. The nonlinear circular states andnonlinear elliptical states are constructed and their nonclassicality are studied. The resultsindicate that they all have the oscillation of the photon number distribution and negativityof Wigner function. Meanwhile, nonlinear circular states and nonlinear elliptic statesare compared. These nonlinear states have rather different non-classical properties fromthose of usual even and odd circular states and even and odd elliptical states. When asmall number of coherent states superposition, the nonlinear elliptical states show moresignificant effect of the non-classical than usual the elliptical states.