Optical Ramsey interferences on laser cooled and trapped atoms, detected by electron shelving

Abstract

Based on a new detection scheme optical Ramsey fringes on the magnesium intercombination transition ( λ=457 nm) have been demonstrated with a resolution of 4 kHz and an accuracy of 1 Hz ( Δv v ≈2×10 −15 ) using laser cooled and trapped atoms. Applying a pulsed excitation scheme to the trapped ensemble, the Ramsey signals are nearly undisturbed by the relativistic Doppler effect and phase errors of the Ramsey zones. The detection is based on the quantum amplification due to the electron shelving effect in cooperation with the trap dynamics, monitored as decrease of the trap fluorescence induced by the fast trapping transition. Simultaneously recorded Ramsey interferences on a thermal atomic beam allowed a direct measurement of the second order Doppler shift. The relevance of the experiment to future optical frequency standards achieving a stability and an accuracy of better than 10 −15 as well as applications of this system for atom interferometry are discussed.