  Sophisticated Ramsey-based interrogation protocols using composite laser
pulse sequences have been recently proposed to provide next-generation
high-precision atomic clocks with a near perfect elimination of frequency
shifts induced during the atom-probing field interaction. We propose here a
simple alternative approach to the auto-balanced Ramsey (ABR) interrogation
protocol and demonstrate its application to a cold-atom microwave clock based
on coherent population trapping. The main originality of the method, based on
two consecutive Ramsey sequences with different dark periods, is to sample the
central Ramsey fringes with frequency-jumps finely-adjusted by an additional
frequency-displacement concomitant parameter, scaling as the inverse of the
dark-period. The advantage of this displaced frequency-jumps Ramsey (DFJR)
method is that the local oscillator frequency is used as a single physical
variable to control both servo loops of the sequence, simplifying its
implementation and avoiding noise associated with controlling the LO phase.
Compared to the usual Ramsey-CPT technique, the DFJR scheme reduces the
sensitivity of the clock frequency to variations of the CPT sideband ratio and
to the one-photon laser detuning by more than an order of magnitude. This
simple method could be applied in a wide variety of Ramsey-spectroscopy based
applications including frequency metrology with CPT-based and optical atomic
clocks, mass spectrometry, and precision spectroscopy.
