Preparation Of Quantum Light Sources Based On Spontaneous Parametric Down Conversion And Its Applications In Quantum Information

The single and two-photon states,as the two most fundamental quantum states,are at the root of carrying out research into quantum information and have important research significance in quantum information processing and quantum communication.The preparation of photons by spontaneous parametric down-conversion is a scheme that requires low and easily achievable experimental conditions.The principle is to use the non-linear interactions of the crystal to down-convert the pump light into a pair of photons that are highly correlated in terms of time,polarization and frequency.As soon as one of these photons is measured,the presence of its twin photon is confirmed.Based on this property,it is possible to determine that a single photon has been prepared without destroying it,compensating for the disadvantages of schemes such as attenuating pulses and atomically coherent media.Also,as the photons produced by spontaneous sub parametric conversion have multiple dimensions of entanglement,they are used to produce quantum entangled light sources for various applications.Therefore,the preparation of single-photon sources and quantum entangled light sources by spontaneous sub parametric conversion has been intensively developed both in theory and experiment.The core work of this paper revolves around the preparation and measurement of single-photon sources and two-photon sources,with the following main elements:(1)The principle of conversion under spontaneous parameters is introduced,and a program is written to calculate the phase matching of BBO crystals type I and type II.The relationship between the phase matching angle,non-common-line angle and crystal cutting angle for conversion under spontaneous parameters is analyzed,and the crystal parameters used in this experiment are selected.(2)Spontaneous parametric down-conversion preparation of single photon states:pumping a single class I BBO crystal,collecting the parametric light through a singlemode fiber,and evaluating the efficiency of single photon generation by comparing the single photon counting with the conformal counting value of the two-way photon,how to collect the parametric light with high quality is the difficult point of this experiment.(3)Preparation of entangled photon pairs by spontaneous parametric downtransfer: pumping two class I BBO crystals glued together vertically in the optical axis,measuring the polarization entanglement properties of the generated two-photon states,and measuring the goodness of the entangled photon pairs by Bell’s inequality and fidelity measurements.(4)It summarizes various models for the preparation of single photon sources and entangled light sources,analyses the advantages and disadvantages of each method,and demonstrates the advantages of converting quantum light sources under spontaneous parameters,and lists the applications of quantum light sources in quantum information.