Preparation Of Non-Gaussian States By Subtract Photon

Quantum communication and quantum computing are two major parts of quantum information science and technology.Their research plays an important role in promoting the development of society.Discrete variables quantum states are widely used quantum resources in quantum communication and quantum computation,its preparation and operation of quantum states have high fidelity which can close to unity,but uauslly at the expense of probabilistic implementations.That unable to meet the needs of quantum information processing.However,continuous-variables quantum states just remedy this defect,its preparation and operation of quantum states are deterministic.Combining these two resources to preparation hybrid entanglement is a research hotspot in recent years.The hybrid entanglement is applied to quantum relay.It is expected that the long-distance entanglement distribution rate will be greatly increased by utilizing the characteristics of deterministic entanglement swapping of continuous variables and long-distance transmission of discrete variables.The optical Schr?dinger cat state is a typical continuous variable non-Gaussian state,which is the superposition of two coherent states with the same amplitude and opposite phase.It shows quantum interference phenomena that can not be observed in the hybrid states of coherent states.It plays an important role in the study of basic physical problems and quantum information.We have carried out the preparation of Schr?dinger cat state in rubidium atomic band(795nm)experimental study.Preparation of non-Gaussian states by subtraction photon and theoretically analyzed impact of phase jitter on the preparation of optical Schr?dinger cat state.These two works provide experimental and theoretical guidance for the effective preparation of optical Schr?dinger cat state in the laboratory,and they provide experimental basis for the next step of hybrid quantum relay.The completed main research works are as follows:1.We experimentally generated 795 nm vacuum squeezed state light field by using an optical parametric oscillator based on class I PPKTP crystal.We carry out the preparation of non-Gaussian state by method of subtract photon on the basis of producing vacuum squeezed state.A small part of the optical field of the vacuum squeezed state is reflected to the single photon detector.The generation of the subtracted photon vacuum squeezed state is predicted by photon counting.The orthogonal component of the prepared quantum state is measured by the balanced homodyne detector.It is found that the distribution of the orthogonal component of the prepared subtracted photon vacuum squeezed state appears obvious non-Gaussian characteristics,which provides a basis for the preparation of the optical Schr?dinger cat state.2.We study the impact of phase jitter in homodyne detection on the preparation of Cat state.At first,in the case of stable phases we obtain the analytic expression of the marginal distribution of the quadrature noise of a Cat state,and get the measurement set of the quadrature components by computer simulation.Then the measurement set under the condition of phase jitter are acquired by means of transforming the marginal distribution,and the Wigner function of the quantum state is reconstructed using Maximum Likelihood Estimation.We analyze the fidelity of Cat state as well as the origin value W(0,0)of the Wigner function as a function of phase jitter amplitude.It is discovered that the fidelity decreases with increasing of phase jitter amplitude while W(0,0)value is insensitive to phase jitter.Furthermore,the impact of phase jitter on fidelity of Cat state is analyzed for different squeezing degrees and squeezing purities of the input states.The results indicate that the lower squeezing degree or higher squeezing purity,the smaller the influence of phase jitter on fidelity.