Quantum Interference And Photonic Spin-Hall Effects In Atomic Media

Interaction between atoms and light is a main branch of quantum optics,and it has important applications in the fields of quantum computation,quantum communication,quantum precision measurement,etc.The interaction of atoms with coherent light(laser)creates atomic coherence,which produces various novel effects,such as electromagnetically induced transparency(EIT),lasing without inversion(LWI),enhancement of refractive index without absorption,etc.Atomic coherence is very important in enhancing the efficiency of four-wave mixing(FWM),manipulating the group velocity of light pulses,preparing nonclassical light,etc.Based on the traditional content of quantum optics,developing new interaction mechanisms between atoms and light is a central goal of quantum optics.Recently,spinorbit interaction of light(SOIL)has attracted enormous interest and underpins the chiral quantum optics,which investigates various chiral light-matter interaction.In this thesis,we firstly introduce EIT,FWM,SOIL,spin-Hall effect of light(SHEL),etc.and review the research development and applications.Based on the atomic coherence and quantum interference,we investigate the quantum interference and its manipulation in multi-level atomic systems,multi-channel frequency conversion via FWM,SHEL in atomic media and its enhancement.The main works are as following:1)We investigate the quantum interference in a V-type three-level atomic system consisting of two excited states and one ground state.The strong quantum interference between the two transition channels requires(i)the frequency splitting of the two excited states is less than the spontaneous decay rate;(2)the dipole moment matrix elements of the two transition channels have parallel components.Under these two conditions,the two transitions can be coupled to the same vacuum mode,leading to the quantum interference.The probe absorption spectrum is dramatically modified by the interference.When the two dipole moment matrix elements are orthogonal to each other,there is no quantum interference and the absorption spectrum is just a superposition of two Lorentzian profiles.When they have parallel components,the quantum interference is destructive and the absorption on resonance is suppressed.When they have anti-parallel components,the quantum interference is constructive and the absorption on resonance is enhanced.When the frequency splitting of the two excited states are much larger than the spontaneous decay rate,quantum interference is very weak and its effect on the absorption can be ignored.Comparison between the quantum interference and the double-slit interference reveals the same physical mechanism underpinning these two effects.2)We investigate the manipulation and enhancement of quantum interference via dephasing in a ?-type EIT atomic system.The dephasing in atom-light system mainly originates from(i)the atomic level fluctuations due to collisions between atoms and(ii)the phase(or frequency)fluctuations of the interacting field.In dressed-state representation,we calculate the probe absorption including two Lorentzian terms arising from Aulter-Townes splitting(ATS)and one quantum interference term.The quantum interference can be manipulated via correlated atomic level fluctuations or field phase fluctuations.The correlated(anti-correlated)fluctuations can enhance the destructive(constructive)quantum interference and suppress(enhance)the absorption.Then quantum interference vanishes under certain condition,and the absorption is determined by ATS.We also investigate the influence of the Rabi frequency of the coupling field on the quantum interference.When the Rabi frequency of the coupling field is less than the spontaneous decay rate,the quantum interference is strong,and it can be efficiently manipulated via dephasing.When the coupling field is very strong,the quantum interference can be ignored.3)We demonstrate simultaneous generation of two blue laser beams at 455 nm and 459 nm via atomic coherence enhanced FWM in Cs vapor.Two pump lasers at 852 nm and 921 nm create strong atomic coherence on 6S1/2(F = 3)?6D3/2 transition,transferring a large fraction of population into the excited state 6D3/2.There are two possible channels through which atoms can decay to the ground state 6S1/2 via intermediate states 7P3/2 or 7P1/2,respectively.Therefore,two FWM processes(6S1/2?6P3/2?6D3/2 ?7P3/2?6S1/2 and 6S1/2?6P3/2?6D3/2?7P1/2?6S1/2)occur simultaneously,converting the pumping lasers at 852 nm and 921 nm to two blue lasers at 455 nm and 459 nm,respectively.An additional intense laser at 895 nm resonant to the 6S1/2(F = 3)?6P1/2 transition significantly improves the efficiency of the frequency conversion.We investigate the influences of detuning and power of the pump lasers and the temperature of the vapor on the conversion efficiency,and find the optimized experimental parameters to simultaneous generate the two blue lasers.4)We show the existence of SHEL in an atomic medium via EIT.The medium is made birefringent by applying an additional linearly polarized coupling light beam.The refractive index and the orientation of the optics axis are controlled by the coupling beam.After transmitting the atomic medium,a linearly polarized probe light beam splits into its two spin components by opposite transverse shifts.With proper choice of parameters,the shifts are about the order of wavelength.In order to precisely measurement the SHEL shifts,we propose a novel measurement scheme based on a balanced homodyne detection(BHD).By properly choosing the polarization,phase,and transverse mode of the local oscillator of the BHD,one can independently measure(i)the SHEL shifts of the two spin components;(ii)the spatial and angular shifts;(iii)the transverse and longitudinal shifts.The measurement precision is estimated to be at the nanometer level provided that the classical noises are suppressed using frequency modulation technique,etc.5)We show that strong absorptive anisotropy can enhance SHEL in an atomic medium.Applying an incoherent pump field,the atomic medium exhibits strong absorptive anisotropy due to optical pumping.Under typical experimental conditions,the SHEL shift is predicted to be a few microns.We demonstrate the transition between the spatial and angular shifts when the frequency of the input beam changes.The underlying physics of the enhanced SHEL is similar to that of the enhanced SHEL near the Brewster's angle of an interface,revealing a profound connection between the two systems.The innovations are as follows:?.We systematically study the various dephasing mechanisms in EIT atomic systems and the effects of dephasing on the quantum interference.?.We demonstrate the simultaneous frequency conversion from infrared lasers at 852 nm and 921 nm to two blue lasers at 455 nm and 459 nm.We show that a repumping laser at 895 nm can significantly improve the conversion efficiency.We find the optimized experimental parameters to simultaneously generate the two blue lasers with high efficiencies.?.We show the existence of SHEL in atomic media via anisotropy and extend the investigation of SHEL from the traditional systems(such as interface between two media,etc.)to the atomic systems.The transverse SHEL shifts are always together with the longitudinal shifts.Our work provides a new interaction mechanism between atoms and light.?.We propose a novel measurement scheme base on a BHD to investigate SHEL.Compared to the traditional quadrant-detector-based measurement combined with the weak-value enhancement,this scheme can independently measure the shifts in different degrees of freedom.The measurement precision is estimated to be at the nanometer level.