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Single Ca + Ion Trapping toward Precise Frequency Measurement of the 4 2 S 1/2 - 3 2 D 5/2 Transition

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

Published Aug 31, 2005• 2 citations
OpenAlex

Abstract

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

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Progress on the evaluation of systematic frequency shifts is described in the development of the optical frequency standard based on single-trapped ${}^{40}$Ca${}^{+}$ with a ``clock'' transition at 729 nm. The overall systematic uncertainty of the 4$s$ ${}^{2}$$\phantom{\rule{-0.16em}{0ex}}{S}_{1/2}$-3$d$ ${}^{2}$$\phantom{\rule{-0.16em}{0ex}}{D}_{5/2}$ clock resonance has been characterized to be 7.8 \ifmmode\times\else\texttimes\fi{} 10${}^{\ensuremath{-}16}$. This uncertainty is at a level similar to the Cs fountain primary standard, while the potential stability for the ${}^{40}$Ca${}^{+}$ clock exceeds that of Cs.

Physical Review A•Nov 21, 2011•34 citations
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
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.
An optical frequency standard based on the $S\text{\ensuremath{-}}D$ transition of trapped 43Ca+^{43}\mathrm{Ca}^{+}43Ca+ is possible by using just laser diodes for cooling and probing. We discuss two open problems related to the feasibility of this frequency standard, the attainable frequency uncertainty and the method of initial-state preparation. The uncertainty of the clock transition frequency can be so small as $1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}$. Using a laser system consisting of three lasers at different detunings and polarizations, the ion can be cooled down to the Lamb-Dicke regime and then prepared in the m=0m=0m=0 state within a period much shorter than the cooling period without being heated. The details of our numerical simulation are described.
An optical frequency chain referenced to a Cs atomic clock has been used to measure directly the frequency of the electric quadrupole allowed $5s^{2}S_{1/2}\ensuremath{-}4d^{2}D_{5/2}$ transition at 445 THz in a single, trapped, and laser cooled 88Sr+{}^{88}{\mathrm{Sr}}^{+}88Sr+ ion. A transition frequency, ${f}_{S\ensuremath{-}D}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}444779044095.4\mathrm{kHz}$ with an estimated standard uncertainty of 0.2 kHz has been determined. Intrinsic offsets of the probed ion transition in the current experiment are calculated to be at the ${10}^{\ensuremath{-}15}$ level.
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.
Progress on the evaluation of systematic frequency shifts is described in the development of the optical frequency standard based on single-trapped 40{}^{40}40Ca+{}^{+}+ with a ``clock'' transition at 729 nm. The overall systematic uncertainty of the 4sss 2{}^{2}2S1/2\phantom{\rule{-0.16em}{0ex}}{S}_{1/2}S1/2​-3ddd 2{}^{2}2D5/2\phantom{\rule{-0.16em}{0ex}}{D}_{5/2}D5/2​ clock resonance has been characterized to be 7.8 \ifmmode\times\else\texttimes\fi{} 10${}^{\ensuremath{-}16}$. This uncertainty is at a level similar to the Cs fountain primary standard, while the potential stability for the 40{}^{40}40Ca+{}^{+}+ clock exceeds that of Cs.