Hannover 2003 – wissenschaftliches Programm
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A: Atomphysik
A 21: Ultraschnelle Ph
änomene + Spektroskopie 2
A 21.4: Vortrag
Freitag, 28. März 2003, 14:45–15:00, F128
Reduction of phase-shifts in a neutral atom frequency standard approaching 10−15 uncertainty — •Guido Wilpers, E. Anne Curtis, Christopher W. Oates, and Leo Hollberg — National Institute of Standards and Technology, 325 Broadway, Boulder, Co. 80305, USA
Optical frequency standards utilizing laser-cooled atoms or ions have already reached a level of stability superior to Cs atomic clocks running at microwave frequency. However, the inaccuracy is still an order of magnitude worse than the 1×10−15 level reached in state of the art Cs fountains. For the use of neutral atoms there are two critical issues: 1) frequency shifts resulting from a residual Doppler-effect in non-optimal wavefronts of the pulsed laser beams that are used for atom interferometry in the time domain, 2) phase-chirps of the pulsed laser beams. At present these shifts dominate the total relative uncertainty of 5.6×10−14 achieved in the calcium frequency standard we operate at NIST. Here we utilize Doppler-cooled atoms with an rms-velocity of 0.7 m/s.
Applying a new second stage cooling method we achieve rms-velocities of less than 5 cm/s, thereby reducing the Doppler-shift by about a factor of 10. Moreover, we can launch the Doppler-cooled ensembles at velocities of up to 3 m/s without increasing the rms-velocity. Therefore, we can measure the dependence of the shifts in different types of atom interferometers as a function of atom velocity or time separation of the pulses. This will allow us to distinguish between the different contributions to the Doppler effect as well as the phase chirp and should enable us to reduce these contributions to the uncertainty to below 10−15.