A Cs-Based Optical Frequency Measurement Using Cross-Linked Optical and Microwave Oscillators

• Main Authors: Tamm, Chr, Huntemann, N, Lipphardt, B, Gerginov, V, Nemitz, N, Kazda, M, Weyers, S, Peik, E
• Format: Journal Article
• Language: English
• Published: 30-10-2013
• Subjects: Physics - Atomic Physics; Physics - Optics
• DOI: 10.48550/arxiv.1310.8190

Phys. Rev. A 89, 023820 (2014) We describe a measurement of the frequency of the 2S1/2(F = 0) - 2D3/2(F' =
2) transition of 171Yb+ at the wavelength 436 nm (frequency 688 THz), using a
single Yb+ ion confined in a Paul trap and two caesium fountains as references.
In one of the fountains, the frequency of the microwave oscillator that
interrogates the caesium atoms is stabilized by the laser that excites the Yb+
reference transition with a linewidth in the hertz range. The stability is
transferred to the microwave oscillator with the use of a fiber laser based
optical frequency comb generator that also provides the frequency conversion
for the absolute frequency measurement. The frequency comb generator is
configured as a transfer oscillator so that fluctuations of the pulse
repetition rate and of the carrier offset frequency do not degrade the
stability of the frequency conversion. The phase noise level of the generated
ultrastable microwave signal is comparable to that of a cryogenic sapphire
oscillator. For fountain operation with optical molasses loaded from a laser
cooled atomic beam source, we obtain a stability corresponding to a fractional
Allan deviation of $4.1\times 10^{-14}\ (\tau/\text{s})^{-1/2}$. With the
molasses loaded from thermal vapor and an averaging time of 65 h, we measure
the frequency of the Yb+ transition with a relative statistical uncertainty of
$2.8\times10^{-16}$ and a systematic uncertainty of $5.9\times10^{-16}$. The
frequency was also simultaneously measured with the second fountain that uses a
quartz-based interrogation oscillator. The unperturbed frequency of the Yb+
transition is realized with an uncertainty of $1.1\times10^{-16}$ that mainly
results from the uncertainty of the blackbody shift at the operating
temperature near 300 K. The transition frequency of 688 358 979 309 307.82(36)
Hz, measured with the two fountains, is in good agreement with previous
results.