Chad Hoyt

Direct excitation of the forbidden clock transition in neutral 174Yb atoms confined to an optical lattice.

We report direct single-laser excitation of the strictly forbidden (6s2)1S0 <--> (6s6p)3P0 clock transition in 174Yb atoms confined to a 1D optical lattice. A small (approximately 1.2 mT) static magnetic field was used to induce a nonzero electric dipole transition probability between the clock states at 578.42 nm. Narrow resonance linewidths of 20 Hz (FWHM) with high contrast were observed, demonstrating a resonance quality factor of 2.6 x 10(13). The previously unknown ac Stark shift-canceling (magic) wavelength was determined to be 759.35 +/- 0.02 nm. This method for using the metrologically superior even isotope can be easily implemented in current Yb and Sr lattice clocks and can create new clock possibilities in other alkaline-earth-like atoms such as Mg and Ca.

Observation and Absolute Frequency Measurements of the 1S0 - 3P0 Optical Clock Transition in Neutral Ytterbium

We report the direct excitation of the highly forbidden (6s2) 1S0 <--> (6s6p) 3P0 optical transition in two odd isotopes of neutral ytterbium. As the excitation laser frequency is scanned, absorption is detected by monitoring the depletion from an atomic cloud at approximately 70 microK in a magneto-optical trap. The measured frequency in 171Yb (F=1/2) is 518,295,836,591.6 +/- 4.4 kHz. The measured frequency in 173Yb (F=5/2) is 518,294,576,847.6 +/- 4.4 kHz. Measurements are made with a femtosecond-laser frequency comb calibrated by the National Institute of Standards and Technology cesium fountain clock and represent nearly a 10(6)-fold reduction in uncertainty. The natural linewidth of these J=0 to J=0 transitions is calculated to be approximately 10 mHz, making them well suited to support a new generation of optical atomic clocks based on confinement in an optical lattice.

Magnetic field-induced spectroscopy of forbidden optical transitions with application to lattice-based optical atomic clocks

We develop a method of spectroscopy that uses a weak static magnetic field to enable direct optical excitation of forbidden electric-dipole transitions that are otherwise prohibitively weak. The power of this scheme is demonstrated using the important application of optical atomic clocks based on neutral atoms confined to an optical lattice. The simple experimental implementation of this method--a single clock laser combined with a dc magnetic field--relaxes stringent requirements in current lattice-based clocks (e.g., magnetic field shielding and light polarization), and could therefore expedite the realization of the extraordinary performance level predicted for these clocks. We estimate that a clock using alkaline-earth-like atoms such as Yb could achieve a fractional frequency uncertainty of well below 10(-17) for the metrologically preferred even isotopes.

Optical frequency/wavelength references

For more than 100 years, optical atomic/molecular frequency references have played important roles in science and technology, and provide standards enabling precision measurements. Frequency-stable optical sources have been central to experimental tests of Einsteins relativity, and also serve to realize our base unit of length. The technology has evolved from atomic discharge lamps and interferometry, to narrow atomic resonances in laser-cooled atoms that are probed by frequency-stabilized cw lasers that in turn control optical frequency synthesizers (combs) based on ultra-fast mode-locked lasers. Recent technological advances have improved the performance of optical frequency references by almost four orders of magnitude in the last eight years. This has stimulated new enthusiasm for the development of optical atomic clocks, and allows new probes into nature, such as searches for time variation of fundamental constants and precision spectroscopy.

Stable Laser System for Probing the Clock Transition at 578 nm in Neutral Ytterbium

We describe a new laser system we have developed to probe the ultra-narrow 1S0 harr 3P0 clock transition at 578 nm in neutral ytterbium. The yellow light is produced by sum frequency generation in a periodically poled waveguide. With approximately 100 mW each from a fiber laser and Nd:YAG laser, we produce 10 mW of visible light. Stabilization of the laser to a resonance of a high finesse, environmentally isolated cavity has enabled resolution of spectroscopic features as narrow as 5 Hz.

Stability Measurements of the Ca and Yb Optical Frequency Standards

The paper describes two types of optical atomic clocks. The first is based on freely expanding calcium atoms and is optimized for experimental simplicity and high stability. The second is based on Yb atoms confined to an optical lattice that is designed to yield minimal shifts for the clock transition at 578 nm. Measurements of the effective beatnote between the clocks via a femtosecond-laser frequency comb show a fractional frequency instability of <5 times 10-16 @ 100 s averaging time

Optical clocks with cold atoms

This paper discusses an optical atomic clock that uses a narrow atomic resonance to control the frequency of a spectrally narrow laser source. The atomically controlled frequency of the laser gives the clock oscillation frequency as an optical output and provides the stable reference for frequency and timing.

THE Yb OPTICAL LATTICE CLOCK

At the previous Symposium on Frequency Standards and Metrology, H. Katori proposed using IS0 ---->3pO transitions in alkaline earth like atoms to make high performance optical clocks based on large numbers of neutral atoms tightly confined in an optical lattice. 1 This proposal was based on the use of Sr atoms, as were the initial experiments.24 In 2004 Porsev et al. proposed the use of the analogous transition in Yb at 578 nm,5 and we have been developing lattice clocks based on Yb over the past four years. While there are considerable similarities between the Sr and Yb atomic systems, there are also some important differences. Most significantly, Yb has an

Observation of 20 Hz-wide optical clock spectra in even-isotope Yb atoms confined to an optical lattice

We report the first spectroscopy of optical lattice-confined Yb atoms. We demonstrate 20 Hz linewidths using the highly forbidden clock transition (¹S₀-³P₀) in metrologically superior even-isotope ¹⁷⁴Yb atoms in a one-dimensional optical lattice.

Absolute frequency measurements of the /sup 1/S/sub 0/-/sup 3/P/sub 0/ optical clock transition at 578 nm in neutral Yb

This work has focused on two atoms, Sr and Yb, due in part to the relatively high abundance of their odd isotopes, the use of which is necessary for appreciable direct excitation probability. The Sr clock transition has been measured (with an uncertainty of 20 kHz) using atoms in a magneto-optic trap (MOT), and has been excited with atoms confined in a one dimensional lattice. Here we report direct excitation of the Yb clock transition (at 578 nm) with atoms in a second-stage MOT, and the first fs-laser comb-based absolute measurements of the clock frequency for two different isotopes. These measurements lead to a nearly millionfold improvement in our knowledge of the transition frequencies, an important step toward Doppler-free spectroscopy of Yb atoms in a lattice.