Quantum State Engineering Based On Quantum Catalysis

Non-classical light field plays an important role in quantum optics and quantum informatics because of its unique properties.So it is very important to study the preparation and properties of nonclassical light fields.Quantum informatics is a new subject which develops with quantum computer and quantum communication as the main content.Quantum informatics,taking qubit as its carrier,calculates or operates according to the principles of quantum mechanics,which makes Quantum informatics superior to classical informatics.Non-classical quantum state has its important role in quantum information processing.The main work of this thesis is as follows:1.On the basis of the quantum catalysis and two-mode squeezing,we propose a scheme for generating such a quantum state;non-Gaussian quantum state named as Laguerre-polynomial-weighted squeezed state when accompanied by squeezed vacuum and any number Fock state as inputs.Then the non-classical properties of generated state are investigated by Wigner function and squeezing degree.Based on the analytical expressions,our numerical calculations show that the degree of squeezing can be improved by modulating parameters of r,? and m.In addition,the Wigner function presents obvious non-Gaussianity and has negative region which is an indicator of the non-classicality.The negative volume can become bigger as the increasing catalysis photon number and squeezing parameter.In a word,we have realized the improvement of non-classicality of squeezed vacuum by parametric conversion and catalysis process.These results provide a solid theoretical basis for further study of multi-mode quantum catalysis and quantum information as well as quantum computation.2.Based on the conditional measurement and beam splitters,multi-photon catalysis is introduced to each mode of even entangled coherent states(EECSs).The resulted states belong to a kind of Laguerre polynomials excited EECSs.Then the entanglement properties of resulted states are examined according to EPR correlation,Concurrence and the teleportation fidelity.For the symmetrical beam splitters,these three quantities can be improved by multi-photon catalysis(? 3)and only EPR correlation can also be enhanced by zero-photon catalysis.Our optimal results over transmissivities of beam splitters show that the unit Concurrence can be achieved for all non-zero photon catalysis which indicates that the optimized output approaches Bell-type state.In addition,two single-photon catalysis and zero-photon catalysis present better performance for the improvement of both the EPR correlation and the teleprtation fidelity in small and large amplitude regions,respectively.Particularly,it is interesting to notice that both of them can be optimized to be constant by zero-photon catalysis when the amplitude exceeds a certain threshold.According to the EPR correlation and the Concurrence,we further investigated the entanglement properties of the LPE-EECSs.Under symmetrical beam splitters case the EPR correlation and the Concurrence can only be improved by multi-photon catalysis(m = n ? 3),and the corresponding values increase as the increasing catalysis photon number.However,it is interesting that the EPR correlation can be enhanced by zero-photon catalysis.