Optical strontium clock is now better candidate for 'new' second

Strontium atoms are cooled and stored in an ultra-high-vacuum chamber. One of the blue fluorescent blobs is a cloud of cold strontium atoms. (Photo: PTB)


Braunschweig, Germany--Scientists at the Physikalisch-Technische Bundesanstalt (PTB) have measured the influence of the ambient temperature on strontium atoms for the first time, potentially reducing the measurement uncertainty of optical strontium clocks by one order of magnitude.1 Such clocks, which use neutral strontium atoms as the frequency generator, are considered one of the top candidates for the definition of a "new" second.

Previously, the influence of the ambient temperature could only be derived theoretically. The PTB results might well spark interest also in geodesy and in fundamental physical research (helping to answer the question as to whether fundamental constants such as the fine-structure constant are really constant).

Due to the higher frequency of optical radiation, optical clocks are more accurate than microwave clocks, which are currently used in the form of cesium atomic clocks to "produce" the second. In an optical strontium clock, a cloud of neutral strontium atoms is cooled down in two steps by means of laser radiation until the atoms exhibit a speed of only a few centimeters per second. An optical lattice ensures that the atoms are trapped.

Ambient temprature the problem
Unfortunately, strontium atoms react relatively strongly to changes in the ambient temperature; their atomic levels are then shifted in energy, which causes the clock to become inaccurate. This is the greatest contribution to the uncertainty of this type of clock.

To measure this phenomenon, the PTB scientists amplified it by using a static electric field rather than the alternating electromagnetic field of blackbody radiation. They constructed a parallel-plate capacitor whose electric field is known to a few-tens-ppm accuracy. For this purpose, the distance between the two plates, which amounted to 0.5 cm, may only vary by a few 100 nm over its length of 7 cm; the same applies to the accuracy of the distance.

The PTB scientists measured the influence of electromagnetic fields on the two decisive (for their clock) eigenstates in the strontium atom. In this way, they determined its uncertainty contribution to the total measurement uncertainty to 5 x 10-18. Because just this influence had, to date, been the most restrictive influence on the total measurement uncertainty, one can expect the next frequency measurements of the clock as a whole to lie well below the previously attained 1 x 10-16.

1. Middelmann, T. et al., Physical Review Letters, 109, 263004 (2012) http://prl.aps.org/abstract/PRL/v109/i26/e263004

Most Popular Articles


Femtosecond Lasers – Getting the Photons to the Work Area

Ultrashort-pulse lasers, both picosecond and femtosecond, are now available from a large number of manufacturers, with new players entering the field at a ra...

Ray Optics Simulations with COMSOL Multiphysics

The Ray Optics Module can be used to simulate electromagnetic wave propagation when the wavelength is much smaller than the smallest geometric entity in the ...

Multichannel Spectroscopy: Technology and Applications

This webcast, sponsored by Hamamatsu, highlights some of the photonic technology used in spectroscopy, and the resulting applications.

Handheld Spectrometers

Spectroscopy is a powerful and versatile tool that traditionally often required a large and bulky instrument. The combination of compact optics and modern pa...

Opportunities in the Mid-IR

The technology for exploiting the mid-IR is developing rapidly:  it includes quantum-cascade lasers and other sources, spectroscopic instruments of many...
White Papers

Accurate LED Source Modeling Using TracePro

Modern optical modeling programs allow product design engineers to create, analyze, and optimize ...

Miniature Spectrometers for Narrowband Laser Characterization

In less than 60 years, lasers have transformed from the imagined “ray gun” of science fiction int...

Improve Laser Diode Performance by Reducing Output Cable Inductance using Twisted Pair Cable

The intent of this article is to provide information regarding the performance of twisted pair ca...
Technical Digests

OPTICAL COATINGS: Evolving technology produces new benefits

The antireflection, high-reflection, and/or spectral characteristics provided by optical coatings...

REMOTE FIBER-OPTIC SENSING: Data in abundance from difficult environments

The use of optical fibers to measure strain, temperature, and other parameters at desired points ...

SCANNERS FOR MATERIALS PROCESSING: Serving demanding applications

Galvanometer-based scanners are an essential component in laser-based materials-processing system...

Click here to have your products listed in the Laser Focus World Buyers Guide.


SCHOTT and Applied Microarrays Establish Distribution Partnership for NEXTERION® Products

01/22/2013 SCHOTT and Applied Microarrays, Inc. have established a partnership for the distribution of SCHOT...

SCHOTT North America and Space Photonics, Inc. Sign Exclusive Licensing Agreement for Covert Communications Technology

01/22/2013 WASHINGTON, D.C.—October 18, 2012—Space Photonics Inc. and SCHOTT North America, Inc. today annou...
Social Activity
Copyright © 2007-2015. PennWell Corporation, Tulsa, OK. All Rights Reserved.PRIVACY POLICY | TERMS AND CONDITIONS