Precision measurement of the fine structure constant based on atom interferometry

Preliminary result of the fine structure constant measurement is presented, which is based on an atom interferometric method. The value for the fine structure constant is derived from the precision measurement of the recoil velocity of cesium atoms due to the coherent scattering of a single photon. The current uncertainty of the measurement is 7.4 ppb in α. The analysis of the major systematic effects is presented and the last yet not completely resolved potential systematic effect is discussed. It is due to cold cesium background atoms constituting a dielectric environment with non-unity index of refraction. Among the other effects discussed, especially this systematic effect may be of importance for future high precision atom interferometers like HYPER aiming at the sub-ppb level of uncertainty in the determination of α.