arXiv subjects

Thomas E. Parker

Publications and source records attributed to Thomas E. Parker.

4 recordsLinked to original sources

arXiv2020

Optical Atomic Clock Comparison through Turbulent Air

We use frequency comb-based optical two-way time-frequency transfer (O-TWTFT) to measure the optical frequency ratio of state-of-the-art ytterbium and strontium optical atomic clocks separated by a 1.5 km open-air link. Our free-space measurement is compared to a simultaneous measurement acquired via a noise-cancelled fiber link. Despite non-stationary, ps-level time-of-flight variations in the free-space link, ratio measurements obtained from the two links, averaged over 30.5 hours across six days, agree to $6\times10^{-19}$, showing that O-TWTFT can support free-space atomic clock comparisons below the $10^{-18}$ level.

physics.optics↗

arXiv2020

Frequency Ratio Measurements with 18-digit Accuracy Using a Network of Optical Clocks

Atomic clocks occupy a unique position in measurement science, exhibiting higher accuracy than any other measurement standard and underpinning six out of seven base units in the SI system. By exploiting higher resonance frequencies, optical atomic clocks now achieve greater stability and lower frequency uncertainty than existing primary standards. Here, we report frequency ratios of the $^{27}$Al$^+$, $^{171}$Yb and $^{87}$Sr optical clocks in Boulder, Colorado, measured across an optical network spanned by both fiber and free-space links. These ratios have been evaluated with measurement uncertainties between $6\times10^{-18}$ and $8\times10^{-18}$, making them the most accurate reported measurements of frequency ratios to date. This represents a critical step towards redefinition of the SI second and future applications such as relativistic geodesy and tests of fundamental physics.

physics.atom-ph↗

arXiv2018

A null test of General Relativity: New limits on Local Position Invariance and the variation of fundamental constants

We compare the long-term fractional frequency variation of four hydrogen masers that are part of an ensemble of clocks comprising the National Institute of Standards and Technology,(NIST), Boulder, timescale with the fractional frequencies of primary frequency standards operated by leading metrology laboratories in the United States, France, Germany, Italy and the United Kingdom for a period extending more than 14 years. The measure of the assumed variation of non-gravitational interaction,(LPI parameter, $β$)---within the atoms of H and Cs---over time as the earth orbits the sun, has been constrained to $β=(2.2 \pm 2.5)\times 10^{-7}$, a factor of two improvement over previous estimates. Using our results together with the previous best estimates of $β$ based on Rb vs. Cs, and Rb vs. H comparisons, we impose the most stringent limits to date on the dimensionless coupling constants that relate the variation of fundamental constants such as the fine-structure constant and the scaled quark mass with strong(QCD) interaction to the variation in the local gravitational potential. For any metric theory of gravity $β=0$.

gr-qc↗

arXiv2008

The absolute frequency of the 87Sr optical clock transition

The absolute frequency of the 1S0-3P0 clock transition of 87Sr has been measured to be 429 228 004 229 873.65 (37) Hz using lattice-confined atoms, where the fractional uncertainty of 8.6x10-16 represents one of the most accurate measurements of an atomic transition frequency to date. After a detailed study of systematic effects, which reduced the total systematic uncertainty of the Sr lattice clock to 1.5x10-16, the clock frequency is measured against a hydrogen maser which is simultaneously calibrated to the US primary frequency standard, the NIST Cs fountain clock, NIST-F1. The comparison is made possible using a femtosecond laser based optical frequency comb to phase coherently connect the optical and microwave spectral regions and by a 3.5 km fiber transfer scheme to compare the remotely located clock signals.

physics.atom-ph↗