Polarization Squeezed 795-nm Quantum Light Source And Quantum-enhanced Rubidium Atomic Magnetometer

Polarization squeezed light is characterized with polarization of light.Two orthogonally polarized light combine to a new state at a polarization beam splitter,if at least one of these stats is squeezed,the new state could be squeezed under certain phase.Polarization squeezing could interact with atomic ensembles for sensing the information of atomic spin.Compared with classical coherent light,polarization squeezed state has noise background lower than the shot noise limit,thus get higher signal-to-noise ratio.Such quantum source is potential in precise measurement.Polarization squeezing derives from quadrature squeezing,and optical parametric oscillator is the best method for generating frequency tunable squeezed light.Based on the cavity-enhanced nonlinear interaction,light frequency and its noise feature will modified.The output photon pairs have strong quantum correlation,demonstrating the squeezing characteristic.Squeezed light plays an important role in fields of quantum optics.For example,quantum networks,quantum information,quantum memory and precise measurement.In the atomic-based optical precise measurement,sensitivity is limited by the classical limit,coming from the photon shot noise and atomic projection noise.Polarization squeezing of light and spin squeezing of atoms are the two methods to further increase sensitivity.For example,polarization squeezed light resonant with at atomic transition line could be used to sense the spin precession of atomic ensembles,detecting the atomic states.Atomic ensemble has its own response frequency.To fulfill the interaction,polarization squeezing should be prepared at specific frequencies.We prepared a quantum light source at 795 nm which is characterized by polarization squeezing.We built an optical-atomic magnetometer based on nonlinear magneto-optical rotation,and explored the sensitivity enhancement of magnetic field measurement with squeezed light.The research consists of the following parts:(1)Designed and built the semi-monolithic cavity,accomplished cavityenhanced frequency doubling with PPKTP crystal.Investigated the conversion efficiency,beam quality and stability in frequency doubling process.Analyzed the characters of intra-cavity loss,thermal absorption and thermal stability.At low power regime,made the comparison with bow-tie type cavities;(2)Built a bow-tie type cavity,investigate the difference of nonlinear crystals.Compared the advantages and disadvantages of PPKTP,LBO and Bi BO in frequency doubling.This will be a reference for nonlinear crystal chosen at this wavelength;(3)Prepared quadrature squeezing with OPO,obtained the highest squeezing at 795 nm;polarization squeezing was generated with phase locked,the squeezing feature was characterized;(4)Generated polarization squeezing at audio frequency.We analyzed the audio-frequency noise sources and took methods to control them.We found the quantum noise locking method to lock the relative phase between squeezed vacuum and local oscillator,and got flat noise reduction at 2.6-100 k Hz;(5)Built an optical-atomic magnetometer based on NMOR,investigated the sensitivity dependence of light frequency,intensity,etc.Both coherent beam and polarization squeezed light were used in measurements.Quantum enhancement was achieved with the help of squeezed light.There are something new in this work:(1)The newly built semi-monolithic cavity was low loss,stable and had high conversion efficiency,suitable for low power regime.When power increased,however,heat accumulated in cavity and caused thermal instability,then it was beneficial to use bow-tie type cavity.So cavity design should take power into consideration;(2)We investigated the frequency doubling with different nonlinear crystals,especially the relatively new Bi BO crystal.The comparison of characters and doubling efficiencies is useful for crystal chosen;(3)We investigated the characterization of polarization squeezing,and expanded frequency band to k Hz.We achieved the quantum noise locking in stabilization of relative phase between squeezed vacuum and bright coherent light;similar locking method could be used in other coherent systems;(4)We injected polarization squeezed light into the optical magnetometer,compared with the coherent beam,squeezed light had lower noise background,helped to improve the signal-to-noise ratio,so the measurement sensitivity is increased.The result shown the quantum enhancement of squeezed light in precise measurement.