Addendum: Optically trapped atom interferometry using the clock transition of large ⁸⁷Rb Bose-Einstein condensates

In our original paper (Altin et al 2011 New J. Phys. 13 065020), we presented the results from a Ramsey atom interferometer operating with an optically trapped sample of up to 106 Bose-condensed ⁸⁷Rb atoms in the m _F = 0 clock states. We were unable to observe projection noise fluctuations on the interferometer output, which we attribute to the stability of our microwave oscillator and background magnetic field. Numerical simulations of the Gross-Pitaevskii equations for our system show that dephasing due to spatial dynamics driven by interparticle interactions accounts for much of the observed decay in fringe visibility at long interrogation times. The simulations show good agreement with the experimental data when additional technical decoherence is accounted for, and suggest that the clock states are indeed immiscible. With smaller samples of 5×10 ⁴ atoms, we observe a coherence time of τ = 1.0 ^+0.5 _-0.3 s.