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

Single Ca/sup +/ ion trapping toward precise frequency measurement of the 4 /sup 2/S/sub 1/2/ - 3/sup 2/D/sub 5/2/ transition

K. Matsubara, Y. Li, Masatoshi Kajita, K. Hayasaka, Mizuhiko Hosokawa, S. Urabe

Published Jan 18, 2006• 0 citations
Publisher

Abstract

We are proceeding with a development of an optical frequency standard using a2Sfrac12-2D5/2electric quadrupole transition of Ca+ions in a small radio-frequency trap. We have theoretically confirmed that an uncertainty of-15is attainable in measurement of the2Sfrac12-2D5/2transition frequency. Experimentally, we have developed stable laser-diode systems and observed the quantum jump of single40Ca+ions to the2D5/2state

DOI
10.1109/freq.2005.1574005

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Joint Conference of the European Frequency and Time Forum and IEEE International Frequency Control Symposium (EFTF/IFCS)•Jul 8, 2004•6 citations
We are proceeding with a development of an optical frequency standard using a2Sfrac12-2D5/2electric quadrupole transition of Ca+ions in a small radio-frequency trap. We have theoretically confirmed that an uncertainty of-15is attainable in measurement of the2Sfrac12-2D5/2transition frequency. Experimentally, we have developed stable laser-diode systems and observed the quantum jump of single40Ca+ions to the2D5/2state
Abstract —We are proceeding with a development of an optical frequency standard using a 2 S 1/2 – 2 D 5/2 electric quadrupole transition of Ca + ions in a small radio-frequency trap. We have theoretically confirmed that an uncertainty of <1 x 10 -15 is attainable in measurement of the 2 S 1/2 – 2 D 5/2 transition frequency. Experimentally, we have developed stable laser-diode systems and observed the quantum jump of single 40 Ca + ions to the 2 D 5/2 state. I. I NTRODUCTION The uncertainty of primary frequency standards using Cs atoms reaches around 10 -15 and the inherent limits involved in them are discussed. On the other hand, frequency standards using new materials and methods are proposed for developing more accurate frequency standards. Recently, several groups have measured frequencies of the ionic forbidden transitions in the optical region to apply them to the clock transitions of optical frequency standards [1]. We now proceeds with study on an optical frequency standard using single Ca
Summary form only given. Among the ions proposed for a frequency standard in the optical domain, Ca/sup +/ is one of the most favorable candidates due to its wavelengths accessible with all-solid-state laser systems. This allows to imagine an ultimate experimental setup being simple and compact. The 4S/sub 1/2/-3D/sub 5/2/ electric quadrupole transition at 729 nm with a natural linewidth below 1 Hz serves as clock transition, while laser cooling on one of the resonance lines is carried out at 397 nm. To obtain the small spectral linewidths necessary for a frequency standard performance, it is essential to reduce the residual Doppler broadening caused by the RF heating in the Paul trap. The first-order Doppler broadening of a single ion can be eliminated in the Lamb-Dicke regime where the ion's amplitude of motion is inferior to the emitted wavelength. The main condition for the access of this frequency modulation regime is a high motional frequency of the trapped ion. This is more easily obtained in a low capacitance device and thus traps with reduced dimensions are required. We have set up a miniature ion trap of the Paul-Straubel-type. The stored ions are observed by a photomultiplier in the photon-counting mode as well as by an intensified CCD camera, permitting the visualization of their spatial behavior. Laser cooling of the Ca/sup +/ ions is carried out on the 4S/sub 1/2/-4P/sup 1/2/ resonance line at 397 nm. Progress on the characterization of the trapped single ion as well as on the generation of the involved wavelengths exclusively by solid-state lasers is reported.
The National Institute of Information and Communications Technology in Japan is proceeding with development of an optical frequency standard using an electric quadrupole transition of Ca+ ions in a small radio-frequency trap. The single, trapped 40Ca+ ions are laser cooled to a temperature of <10 mK using extended-cavity diode lasers at 397 nm and 866 nm. In order to measure the electric quadrupole transition, the linewidth of the clock laser diode at 729 nm is reduced to ~66 Hz using an ultra-low-expansion (ULE) cavity. We observed the electric quadrupole transition with a linewidth of ~600 kHz, together with the ionic motional sidebands. We are also developing optical frequency combs without photonic fibers broadening the spectrum. The experimental is now improved in order to observe the narrower linewidth of the quadrupole transition.
We describe experimental investigations of an optical frequency standard based on a single laser-cooled /sup 171/Yb/sup +/ ion confined in a radiofrequency Paul trap. The electric quadrupole transition from the /sup 2/S/sub 1/2 /(F=0) ground state to the /sup 2/D/sub 3/2/(F=2) state at 435.5 nm is used as the reference transition. The transition was resolved with a Fourier-limited width of approximately 30 Hz. In order to investigate the instability and accuracy of a future frequency standard based on the reference transition, a first experiment was done comparing two laser frequencies stabilized individually to two separate ions in different traps. As a result we found a relative frequency instability /spl sigma//sub y/(640 s)=1.5/spl middot/10/sup -15/ for the difference of the two laser frequencies. We also derived a first estimate /spl Theta/(/sup 2/D/sub 3/2/)=(3.9/spl plusmn/1.9)ea/sub 0//sup 2/ for the electric quadrupole moment of the /sup 2/D/sub 3/2/ state.