Study On Nonlocality Quantification Of Frequency Entangled Two-photon Source

Quantum entanglement refers to the nonlocal and nonclassical strong correlation between two or more quantum systems.It plays an important role in fields from the basic research of quantum mechanics to developments of quantum information science.Quantum entanglement is widely applied in quantum secure communication,quantum teleportation,quantum computing,quantum ultra precision measurement,etc.Quantum nonlocality is a key feature of quantum entanglement,which is the main reason why Einstein and others question the completeness of quantum mechanics.Since the 1970s,experiments for testing the quantum nonlocality in two-particle physics system,which use discrete-variables or continuous-variables and violate Bell's inequality,all support the theory of quantum nonlocality.The theory and experimental techniques developed in this process have greatly promoted the development of quantum information science and related disciplines.Frequency entangled two-photon source is a kind of photon sources with correlation in frequency domain.Benefited from the nonlocal dispersion cancellation effect of frequency entangled photons,they are naturally robust to loss and decoherence effects when propagating over long-distance fiber links.Therefore,frequency entangled twophoton source has great application value in fields of quantum communication,quantum metrology and quantum cryptography via optical fiber.Nonlocal dispersion cancellation and nonlocal wavelength-to-time mapping are the unique quantum characteristics of frequency entangled two-photon source.Nonlocal dispersion cancellation can be used to verify quantum nonlocality then ensure the security of quantum information,and can also be used to break the bottleneck of entanglement loss which restricts the development of quantum technology.Nonlocal wavelength-to-time mapping is the basis of temporal quantum ghost imaging,nonlocal spectral imaging and other applications.As far as we know,most of the reported works focus on the theoretical model and phenomenon demonstration under the ideal entanglement condition,and lack of quantification analysis of the involved nonlocality,which limits the application of quantum nonlocality.In this thesis,nonlocality quantification of frequency entangled two-photon source is studied based on the nonlocal wavelength-to-time mapping and the nonlocal dispersion cancellation effect.The main contents are listed as follows:(1)The nonlocal dispersion cancellation effect of the two-photon with finite frequency entanglement is studied theoretically and experimentally.Since previous reports on the nonlocal dispersion cancellation effect are based on the ideal frequency anticorrelated photons,we present a general theoretical model for the nonlocal dispersion cancellation of two-photon with finite frequency entanglement and extend its application from frequency anti-correlated to frequency correlated two-photon source for the first time.The experimental results agree well with the theory,which is of great significance to evaluate the application of nonlocal dispersion cancellation in nonlocality test and enhance loss resistance.(2)The model of nonlocal wavelength-to-time mapping based on frequency entangled two-photon source is improved.We propose and verify that the spectral resolution of the nonlocal wavelength-to-time mapping is determined by the time jitter of the detection system and the pump bandwidth(i.e.two-photon spectral correlation)in the spontaneous parameter down conversion process.By increasing the dispersion,the influence of the time jitter of the detection system on the spectral resolution can be avoided to a certain extent.However,when the dispersion is large enough,the pump bandwidth will set an inherent limit for the resolution.This work gives the basic quantum limits of time domain quantum ghost imaging and nonlocal spectral imaging,which would points out the direction of how to improve the spectral resolution of nonlocal wavelength-totime mapping.(3)Based on the nonlocal wavelength-to-time mapping of frequency entangled photon pair,a hybrid frequency-time spectrograph for the two-photon joint spectrum measurement is proposed.In this scheme,a tunable optical filter is used to filter and calibrate the wavelength of the signal photon,while the wavelength of idler photon is determined by the arrival time measurement and dispersion relation of dispersion mapping.It breaks through the limitation of traditional(local)wavelength-to-time mapping technology,which is only suitable for pulsed laser along with an additional calibration device.This new spectral measurement method is expected to be developed into a versatile tool to measure the properties of entangled photon source,which is of great significance for the development of quantum information and related fields.