Christopher R. Ekstrom

Atom optics using microfabricated structures

We present a novel method for fabricating precisely positioned small openings in thin silicon nitride membranes. Several optical elements for atoms have been constructed, including amplitude diffraction gratings and zone plates, and the results of experiments using these devices are presented. A method for creating a blazed diffraction grating is discussed.

Evaluation of long term performance of continuously running atomic fountains

An ensemble of rubidium atomic fountain clocks has been put into operation at the US Naval Observatory (USNO). These fountains are used as continuous clocks in the manner of commercial caesium beams and hydrogen masers for the purpose of improved timing applications. Four fountains have been in operation for more than two years and are included in the ensemble used to generate the USNO master clock. Individual fountain performance is characterized by a white-frequency noise level below 2 × 10−13 and fractional-frequency stability routinely reaching the low 10−16 s. The highest performing pair of fountains exhibits stability consistent with each fountain integrating as white frequency noise, with Allan deviation surpassing 6 × 10−17 at 107 s, and with no relative drift between the fountains at the level of 7.5 × 10−19/day. As an ensemble, the fountains generate a timescale with white-frequency noise level of 1 × 10−13 and long-term frequency stability consistent with zero drift relative to the worlds primary standards at 1 × 10−18/day. The rubidium fountains are reported to the BIPM as continuously running clocks, as opposed to secondary standards, the only cold-atom clocks so reported. Here we further characterize the performance of the individual fountains and the ensemble during the first two years in an operational environment, presenting the first look at long-term continuous behavior of fountain clocks.

Tests of local position invariance using continuously running atomic clocks

Tests of local position invariance (LPI) made by comparing the relative redshift of atomic clocks based on different atoms have been carried out for a variety of pairs of atomic species. In most cases, several absolute frequency measurements per year are used to look for an annual signal, resulting in tests that can span on order of a decade. By using the output of continuously running clocks, we carry out LPI tests with comparable or higher precision after less than 1.5 years. These include new measurements of the difference in redshift anomalies

One-way temperature compensated fiber link

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Measurements with multiple operational fountain clocks

for hyperfine transitions in

Design and preliminary characterization of the USNO rubidium fountain

{}^{87}\mathrm{Rb}

Optics and Interferometry with Atoms and Molecules

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Coherent excitation of a He∗ beam observed in atomic momentum distributions

{}^{133}\mathrm{Cs}

Miniaturized atomic fountain optical table

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Nonmagnetic UHV optical viewports

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