Imperfect State Preparation Research Articles

Laser-induced noise contribution due to imperfect atomic state preparation in an optically pumped caesium beam resonator

Imperfect atomic state preparation in an optically pumped beam resonator results in over-Poissonian fluctuations of the fluorescence emission of residual unpumped atoms. This excess noise is induced by the frequency noise of the pump laser. We evaluate it theoretically for a three-level atomic system interacting with a noisy laser field, and show that it is predominant within a large range of pumping efficiencies and laser linewidths for usual atomic fluxes. Experimentally, extra noise is detected from ratios of unpumped atoms as low as 0.01% of the atomic flux equal to . This noise source debases the short-term stability of an atomic clock in a flop-in configuration if the proportion of unpumped atoms exceeds 1% of the global atomic flux. In a flop-out configuration this excess noise would decrease the clock stability from a proportion of unpumped atoms of 0.01%.

On the propensity rules for inelastic NH3–rare gas collisions

The observed and ab initio calculated propensity rules for collisions of NH3 with rare gas atoms are found to be in reasonable agreement for NH3–Ar, whereas for NH3–He they show large discrepancies. In order to examine these discrepancies we have calculated state-to-state integral cross sections for collisions of NH3 with He using the close coupling method. The NH3–He interaction potential has been obtained from SCF calculations, augmented by a multipole-expanded damped dispersion energy. Our calculations show that the discrepancies can be accounted for if the cross sections are corrected for the imperfect initial state preparation in the experiment. They also clarify why the discrepancies do not occur to the same extent for NH3–Ar. After comparing our new theoretical results with the experimental data we found that for one experimental cross section for NH3–He the earlier assignment must be corrected.