Extracting the differential phase in dual atom interferometers by   modulating magnetic fields
  We present a new scheme for measuring the differential phase in dual atom interferometers. The magnetic field is modulated in one interferometer, and the differential phase can be extracted without measuring the amplitude of the magnetic field by combining the ellipse and linear fitting methods. The gravity gradient measurements are discussed based on dual atom interferometers. Numerical simulation shows that the systematic error of the differential phase measurement is largely decreased when the duration of the magnetic field is symmetrically modulated. This combined fitting scheme has a high accuracy for measuring an arbitrary differential phase in dual atom interferometers. 
Yu-Ping Wang, Jia-Qi Zhong, Xi Chen, Run-Bing Li, Da-Wei Li, Lei Zhu,   Hong-Wei Song, Jin Wang, and Ming-Sheng Zhan
physics.atom-ph