Longitudinal Ramsey spectroscopy of atoms for continuous operation of optical clocks

Abstract

We propose a longitudinal Ramsey spectroscopy of atoms in a moving optical lattice. Spatially separated magnetic fields, which open the forbidden transition by mixing with the dipole-allowed states, create Ramsey pulses for a probe laser introduced along the optical lattice. Excitation of atoms in the Lamb-Dicke regime by a single probe laser avoids residual Doppler effects as well as mechanical instabilities that deteriorate Ramsey spectroscopy on an atomic beam. Continuous measurement and control of the probe laser improves the Allan deviation as τ −1 for an averaging time τ until the quantum projection noise limit is reached. For 88Sr atoms with an atomic flux of 104 s−1, we speculate a clock instability of 5 × 10−16(τ s−1)−1 down to its floor at around 10−18.