A 2D atom interferometer accelerometer in the horizontal plane

Abstract

The thesis presented here describes the construction and early testing of an atom interferometer able to measure horizontal accelerations along two orthogonal axes. An ultra-high vacuum chamber is built for this cold atom interferometry. Rubidium 87 atoms are prepared in a 2D$^+$ MOT and then directed into the main chamber where they are captured in a 3D MOT. The atoms are cooled from the MOT equilibrium temperature of $\sim$ \SI{140}{mK} down to a few $\mu$K by means of an optical molasses. The atoms are then prepared with a narrow velocity distribution in a magnetically-insensitive ground state using a sequence of optical and microwave pulses. A matter-wave equivalent of the classical Mach-Zehnder interferometer is formed by use of Raman transitions in a $\pi/2-\pi-\pi/2$ pulse sequence. To achieve the maximum sensitivity to acceleration the fringe contrast of the interferometer should be maximised. Adjustments to the chirp rate and alignment of the laser beams improved the fringe contrast by over a factor of 3. Analysis of the noise sources reveals that the noise floor is currently due to instability in the fluorescence detection but will ultimately be due to phase noise in the light driving the Raman transitions. This work demonstrates that the new 2-axis interferometer has better sensitivity than the mechanical accelerometers with which it is compared and points the way to a further tenfold improvement in sensitivity by reducing the noise and increasing the repetition rate.