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CNRS 
Dynamics of a trapped ion cloud in a multipole trap
Aix-Marseille University, Marseille
Physique des Interactions Ioniques et Moléculaires
Metrology Plasma Physics 
Full Description:

Microwave ion clocks designed for deep space navigation have shown a relative stability of few 10-13 over one second. These fluctuations can be lowered down to 10-15 if integrated over one day [1] and there is still room for improvement [2]. Such performances can be reached in a one liter set-up, without any need for laser cooling or laser induced detection scheme. The robustness of the set-up all together with the frequency stability led to the development by the Jet Propulsion Laboratory (NASA) of an ion based microwave clock prototype for the Deep Space Network (http://www.nasa.gov/sites/default/files/files/DSAC_Fact_Sheet.pdf). This device is expected to fly for one year from 2015, to prove its capacities for the long range navigation.Our work concerns fundamental phenomena in optical or microwave frequency standards. Our experimental set-up is strongly connected to the study of the performances of a trapped ion based microwave clock, in collaboration with the French Spatial Agency, CNES. This double trap set-up is inspired by the JPL prototype and allows us to study the impact of the number and temperature of the trapped ions on the assumed performance of a microwave standard.

Ultimate performances of such a microwave clock are limited by the 2nd order Doppler effect. We propose a PhD project  to experimentally quantify the velocity distribution of the ions in different segments of the trap in order to evaluate and control the Doppler contribution and demonstrate the interest of multipole traps for frequency metrology. This is an actual experimental challenge as only indirect measurements have been made via the frequency stability of the device. The project will use laser spectroscopy on the optical clock transition at 729 nm to characterize the second-order Doppler effect, induced by the thermal motion and the rf-driven motion of the trapped ions. Laser excitation along or perpendicular to the trap axis should allow us to compare spectra with and without first order rf-driven motion Doppler effect, in the two different trapping zones, quadrupole and octupole, where  conditions are different. The ion number impacts the line broadening, and the frequency stability will also be experimentally studied as the number of trapped and detectable ions can be varied from few hundreds to hundreds of thousands. To that purpose, we do not plan to use a microwave  source but the ultra-stable laser developed for the excitation of calcium ions on their quadrupole transition at 729 nm (the optical clock transition). This laser is locked onto an ULE cavity for long term stability and bandwidth reduction which is estimated to be of the order of 10 Hz over one second.For this project, we are looking for a student who knows about laser and atomic physics and who is motivated for an ambitious experimental project facing frequency metrology challenges for space applications.


[1] Atomic Clocks and Oscillators for Deep-Space Navigation and Radio Science, J Prestage, G. Weaver, Proceedings of the IEEE 95, 2235 – 2247 (2007)

[2] E. Burt et al. IEEE Trans. Ultrason. Ferroelectr. Freq. Control, 55 (2008) 2586

 



Posted on: 05 February 2015Deadline to apply: 29 March 2015Start Date: 01 October 2015 Duration: 36 months
The Fund category is Mixed Funding and the salary is 20-25k€ annual gross
Doctoral School is Physics and science of matter in the Provence-Alpes-Côte d'Azur Region.

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