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Title: Cancellation of the Collisional Frequency Shift in Caesium Fountain Clocks

Abstract

We have observed that the collisional frequency shift in primary caesium fountain clocks varies with the clock state population composition and, in particular, is zero for a given fraction of the |F=4,m{sub F}=0> atoms, depending on the initial cloud parameters. We present a theoretical model explaining our observations. The possibility of the collisional shift cancellation implies an improvement in the performance of caesium fountain standards and a simplification in their operation.

Authors:
;  [1]; ;  [2]; ;  [3]
  1. National Physical Laboratory, Hampton Road, Teddington, TW11 0LW (United Kingdom)
  2. Joint Quantum Institute and Atomic Physic Division, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, Maryland 20899-8423 (United States)
  3. Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig (Germany)
Publication Date:
OSTI Identifier:
20951234
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review Letters; Journal Volume: 98; Journal Issue: 15; Other Information: DOI: 10.1103/PhysRevLett.98.153002; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ATOMIC CLOCKS; CANCELLATION; CESIUM; OPERATION; PERFORMANCE

Citation Formats

Szymaniec, K., Chalupczak, W., Tiesinga, E., Williams, C. J., Weyers, S., and Wynands, R. Cancellation of the Collisional Frequency Shift in Caesium Fountain Clocks. United States: N. p., 2007. Web. doi:10.1103/PHYSREVLETT.98.153002.
Szymaniec, K., Chalupczak, W., Tiesinga, E., Williams, C. J., Weyers, S., & Wynands, R. Cancellation of the Collisional Frequency Shift in Caesium Fountain Clocks. United States. doi:10.1103/PHYSREVLETT.98.153002.
Szymaniec, K., Chalupczak, W., Tiesinga, E., Williams, C. J., Weyers, S., and Wynands, R. Fri . "Cancellation of the Collisional Frequency Shift in Caesium Fountain Clocks". United States. doi:10.1103/PHYSREVLETT.98.153002.
@article{osti_20951234,
title = {Cancellation of the Collisional Frequency Shift in Caesium Fountain Clocks},
author = {Szymaniec, K. and Chalupczak, W. and Tiesinga, E. and Williams, C. J. and Weyers, S. and Wynands, R.},
abstractNote = {We have observed that the collisional frequency shift in primary caesium fountain clocks varies with the clock state population composition and, in particular, is zero for a given fraction of the |F=4,m{sub F}=0> atoms, depending on the initial cloud parameters. We present a theoretical model explaining our observations. The possibility of the collisional shift cancellation implies an improvement in the performance of caesium fountain standards and a simplification in their operation.},
doi = {10.1103/PHYSREVLETT.98.153002},
journal = {Physical Review Letters},
number = 15,
volume = 98,
place = {United States},
year = {Fri Apr 13 00:00:00 EDT 2007},
month = {Fri Apr 13 00:00:00 EDT 2007}
}
  • We propose an atomic fountain clock with a truncated cold atomic beam to achieve both a low collisional frequency shift and high frequency stability. In this clock, the launching velocity of a cold atomic beam can be swept to reduce the atomic density in the interrogation region for the Ramsey resonance and to increase the atomic density in the detection region. Before the top of the beam arrives at the interrogation region, the cold atomic beam is truncated by turning off the cooling laser beams to remove the unnecessary light shift. The atomic density in the interrogation region is theoreticallymore » evaluated to be 0.04 times that in an ordinary atomic fountain with optical molasses for the same number of detected atoms. The frequency stability limit due to quantum projection noise is calculated to reach 6.4x10{sup -14} in 1 s from the number of detected atoms while the fractional collisional shift is estimated to be {approx}{sup -}2x10{sup -16}.« less
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  • In connection with experiments aiming at the improvement of the cesium atomic beam clock by means of a fountain of laser-cooled cesium atoms, we present expressions for the line shift and line broadening due to collisions between cesium atoms. The coherent collision cross sections occurring in these expressions are calculated by means of the coupled-channels method. The magnitude of the calculated shift implies that spin-exchange collisions are an important factor in limiting the anticipated accuracy of a future cesium fountain clock and of other intended fountain experiments.
  • The electric quadrupole shift is presently the most significant source of uncertainty on the systematic shifts for several single-ion optical frequency standards. We present a simple method for canceling this shift based on measurements of the Zeeman spectrum of the clock transition. This method is easy to implement and yields very high cancellation levels. A fractional uncertainty of 5x10{sup -18} for the canceled quadrupole shift is estimated for a measurement of the absolute frequency of the 5s {sup 2}S{sub 1/2}-4d {sup 2}D{sub 5/2} clock transition of {sup 88}Sr{sup +}.
  • We propose a combination of electromagnetically induced transparency-Raman and pulsed spectroscopy techniques to accurately cancel frequency shifts arising from electromagnetically induced transparency fields in forbidden optical clock transitions of alkaline earth atoms. At appropriate detunings, time-separated laser pulses are designed to trap atoms in coherent superpositions while eliminating off-resonance ac Stark contributions, achieving efficient population transfer up to 60% with inaccuracy <10{sup -17}. Results from the wave-function formalism are confirmed by the density matrix approach.