PhD abstract
Atomic interferometry is a robust experimental method for carrying out high precision measurements, notably of the gravitational acceleration g and the fine structure constant α. Despite the remarkable performance already achieved, the accuracy of today’s best instruments is still limited by several systematic effects, chiefly wave front distortions and spatial inhomogeneities in laser beam intensity.
To quantify their impact, a Monte Carlo simulation was developed that faithfully reproduces two atom interferometry experiments: the LTE atomic gravimeter and the LKB measurement of the h/m ratio. This thesis is devoted to analysing and interpreting the results obtained with these two set ups, with the aim of identifying and modelling the main systematic biases that limit measurement accuracy. For each experiment, a complete numerical model was built for the interferometer sequence and the associated measurement protocols.
Gravimeter : The model allows to evaluate the systematic effect of the laser beam’s Gouy phase. Particular attention was paid to contrast losses caused by intensity inhomogeneity: the resulting phase spread leads to a marked reduction in fringe visibility. These predictions were compared with experimental data obtained by two independent probe pulse techniques that impose a light shift on the atomic energy levels. A model was developed to reproduce the non-monotonic contrast behaviour observed experimentally, taking account of parasitics interferences with the Raman beam. h/m measurement : The Monte Carlo code was adapted to a configuration that uses a Bose-Einstein condensate as a spatial probe for mapping the wave vector distribution and intensity profile of a Bloch beam. After assessing the contributions of the Gouy phase and the beams’ phase curvature, the distribution of measured atomic recoil was modelled when the Bloch beam is diffracted by a circular aperture, reproducing the extra recoil effect seen experimentally in low intensity regions where the recoil exceeds the nominal value hν/c.
Key words
atomic interferometry, quantum metrology, cold atoms, Monte Carlo simulation, wavefront aberrations, Raman transitions, Bloch oscillations.
PhD thesis
Full document (FR) : TEL-05374402