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Joint Conference of the European Frequency and Time Forum and IEEE International Frequency Control Symposium (EFTF/IFCS)

Progress report on the improved linear ion trap physics package

John D. Prestage, Robert L. Tjoelker, G.J. Dick, Lute Maleki

Published Nov 19, 2002• 5 citations
Publisher

Abstract

This article describes the first operational results from the extended linear ion trap frequency standard now being developed at JPL. This new design separates the state selection/interrogation region from the more critical microwave resonance region where the multiplied local oscillator (LO) signal is compared to the stable atomic transition. Hg/sup +/ ions have been trapped, shuttled back and forth between the resonance and state selection traps. In addition, microwave transitions between the Hg/sup +/ clock levels have been driven in the resonance trap and detected in the state selection trap.

DOI
10.1109/freq.1995.483887

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This article describes the first operational results from the extended linear ion trap frequency standard now being developed at JPL. This new design separates the state selection/interrogation region from the more critical microwave resonance region where the multiplied local oscillator (LO) signal is compared to the stable atomic transition. Hg/sup +/ ions have been trapped, shuttled back and forth between the resonance and state selection traps. In addition, microwave transitions between the Hg/sup +/ clock levels have been driven in the resonance trap and detected in the state selection trap.
The frequency stability obtained with an ion-trap-based frequency standard where /sup 199/Hg/sup +/ ions are confined in a hybrid RF/DC linear trap is described. The 40.5-GHz clock transition is measured to be as narrow as 17 mHz representing a quality factor of 2.4*10/sup 12/. A hydrogen maser interrogation of a 37-mHz Hg/sup +/ resonance is used to measure 1*10/sup -15/ stability of the ion resonance at 10000-s averaging time. In another measurement the frequency of the superconducting cavity maser oscillator is steered to follow the Hg/sup +/ clock transition, again providing frequency stability of 1*10/sup -15/ at 10000-s.>
We have previously reported experiments using a linear rf trap to store laser-cooled {sup 199}Hg{sup +} ions. Trapping multiple ions increases the signal-to-noise ratio; yet all ions have equally low second-order Doppler shifts if they are confined along the nodal center line of a linear trap. In such an environment, the 40.5 GHz ground-state hyperfine transition in {sup 199}Hg{sup +} is a candidate for an extremely accurate and stable microwave frequency standard. Our redesigned apparatus will operate at cryogenic temperatures to provide very low background gas pressure (resulting in longer ion storage times and immunity from background pressure shifts) and superconductive shielding against stray magnetic fields. We shall discuss progress on this frequency standard and applications of our apparatus to new cooling and squeezing techniques.
A cryogenic linear rf trap has been constructed to study the accuracy of a clock based on laser cooled /sup 199/Hg/sup +/. Crystals of tens of ions have been observed. The residual micromotion of the ions has been minimized and Ramsey interrogation periods of 100 s have been demonstrated for the 40.5 GHz transition. Systematic shifts to the clock transition due to magnetic field fluctuations as well as heating of the ions during the clock cycle have been evaluated. This system should eventually provide a frequency standard of high precision and accuracy.
The authors report the development of a fieldable frequency standard based on /sup 199/Hg/sup +/ ions confined in a hybrid RF/DC linear ion trap. This trap permits storage of large numbers of ions with reduced susceptibility to the second-order Doppler effect caused by the RF confining fields. A 160-mHz-wide atomic resonance line for the 40.5-GHz clock transition is used to steer the output of a 5-MHz crystal oscillator to obtain a stability of 2*10/sup -15/ for 24000 second averaging times. For long averaging intervals measurements are limited by instabilities in available hydrogen maser frequency standards.>