The optical calcium frequency standards of PTB and NIST

We describe the current status of the Ca optical frequency standards with laser-cooled neutral atoms realized in two different laboratories for the purpose of developing a possible future optical atomic clock. Frequency measurements performed at the Physikalisch-Technische Bundesanstalt (PTB) and the National Institute of Standards and Technology (NIST) make the frequency of the clock transition of 40Ca one of the best known optical frequencies (relative uncertainty 1.2e-14) and the measurements of this frequency in both laboratories agree to well within their respective uncertainties. Prospects for improvement by orders of magnitude in the relative uncertainty of the standard look feasible.Comment: 13 pages, 11 figures, to appear in Comptes Rendus Physiqu

Cold atom Clocks and Applications

This paper describes advances in microwave frequency standards using laser-cooled atoms at BNM-SYRTE. First, recent improvements of the $^{133}$Cs and $^{87}$Rb atomic fountains are described. Thanks to the routine use of a cryogenic sapphire oscillator as an ultra-stable local frequency reference, a fountain frequency instability of $1.6\times 10^{-14}\tau^{-1/2}$ where $\tau$ is the measurement time in seconds is measured. The second advance is a powerful method to control the frequency shift due to cold collisions. These two advances lead to a frequency stability of $2\times 10^{-16}$ at $50,000s for the first time for primary standards. In addition, these clocks realize the SI second with an accuracy of$7\times 10^{-16}$, one order of magnitude below that of uncooled devices. In a second part, we describe tests of possible variations of fundamental constants using$^{87}$Rb and$^{133}$Cs fountains. Finally we give an update on the cold atom space clock PHARAO developed in collaboration with CNES. This clock is one of the main instruments of the ACES/ESA mission which is scheduled to fly on board the International Space Station in 2008, enabling a new generation of relativity tests.Comment: 30 pages, 11 figure

Thulium atoms embedded in noble gas crystals for sensing applications

Narrow linewidth atomic transitions provide opportunities for the development of various quantum technologies. Thulium has an unfulfilled 4$f$ orbital with the electronic configuration similar to Yb$^{3+}$ which is used in several solid-state optical applications. The fine structure of thulium atom is split into ground state ${}^2\mathrm{F}_{7/2}$ and an excited state ${}^2\mathrm{F}_{5/2}$ which is at an energy of 8771 cm$^{-1}$ above the ground state. Because the 4\textit{f} orbital remains submerged underneath the fully filled 5\textit{s}, 5\textit{p} lying near the nucleus, the magnetic dipole transition at 1140 nm has very narrow linewidth and in previous works it was found that the transition was not broadened significantly when trapped in liquid and solid helium. Motivated by this fact that the narrow linewidth transitions observed in thulium coming from the inner shell transitions might have possible applications in building atomic sensors, thulium atoms are studied by trapping them in the solid crystals of argon and neon at cryogenic temperatures. An experimental setup is built to trap the thulium atoms in the ``\textit{matrix}'' of argon and neon, and the samples are prepared on a sapphire substrate and on the tip of a cold multimode fiber. With a home-built high resolution spectrometer for emission spectroscopy and the method of laser absorption spectroscopy, we demonstrated that the magnetic dipole transition is in fact split into multiple components because of the crystal field from argon/neon. In addition to that, we found that the thulium atoms are trapped in multiple trapping sites which are reproducible giving emission at different wavelengths. The experimental setup, methods of sample preparation and high resolution spectroscopy to study the internal structure of the thulium atoms in argon/neon will be discussed.Ph.D

Freie und gespeicherte Calcium-Atome für ein optisches Frequenznormal

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