JILA atomic clocks measure Einstein's general relativity at millimeter scale

JILA physicists have measured Albert Einstein's theory of general relativity at the smallest scale ever, showing that two tiny atomic clocks, separated by just a millimeter or the width of a pencil tip, tick at different rates.

Experiments described in the February issue of Nature suggest how to make atomic clocks 50 times more precise than today's best designs and offer a route to possibly reveal how gravity and quantum mechanics interact with physics.

The National Institute of Standards and Technology and the University of Colorado Boulder operate JILA.

NIST/JILA Fellow Jun Ye said that the most important and exciting result is that we can potentially connect quantum physics with gravity.

Einstein's 1915 theory of general relativity explains large-scale effects such as the gravitational effect on time and has important practical applications. Physicists are still fascinated by the theory, which is more than a century old. NIST scientists have used atomic clocks as sensors to measure relativity more and more precisely, which may help explain how its effects interact with quantum mechanics.

atomic clocks at different elevations tick at different rates according to general relativity The red end of the spectrum has a reduced radiation Frequency when observed in stronger gravity. The clock ticks more slowly at lower altitudes. NIST physicists measured the effect in 2010 by comparing two independent atomic clocks, one positioned 33 centimeters above the other, and the other about 1 foot below.

The JILA researchers have measured the frequencies between the top and bottom of a single sample of ultracold strontium atoms loaded into an optical lattice. The lattice, which can be visualized as a stack of pancakes created by laser beams, has large, flat, thin cakes, and they are formed by less intense light than normally used. The design reduces the distortions in the lattice caused by the scattering of light and atoms, as well as extending the atoms and their matter waves, which show the probability of finding the atoms in certain locations. The energy states of the atoms are so well controlled that they were able to tick between two energy levels in 37 seconds.

The Ye group's innovation, which provided a map of distributions of frequencies across the sample, and their method of comparing two regions of an atom cloud, were important to the new results.

The redshift across the atom cloud was small, consistent with predictions. The differences add up to major effects on the universe and technology, and are too small for humans to see directly. The difference was solved in about 30 minutes of averaging data. Their measurement precision was 50 times better after 90 hours of data.

This is a completely new ballgame, a new regime where quantum mechanics in curved space-time can be explored. Being able to measure the time difference on such a minute scale could allow us to discover that gravity is at the bottom of why our world is classical.

There are many applications for better clocks. Ye suggests atomic clocks can be used as telescopes to look at the deepest corners of the universe and as microscopes to look at quantum mechanics. He is looking for dark matter, which is believed to constitute most matter in the universe. The application of a measurement science called relativistic geodesy is poised to improve models and understanding of the Earth's shape.

More information: Tobias Bothwell, Resolving the gravitational redshift in a millimetre-scale atomic sample, Nature (2022). DOI: 10.1038/s41586-021-04349-7. www.nature.com/articles/s41586-021-04349-7

There are differential clock comparisons with a multiplexed optical lattice clock. www.nature.com/articles/s41586-021-04344-y

Journal information: Nature Citation: JILA atomic clocks measure Einstein's general relativity at millimeter scale (2022, February 16) retrieved 17 February 2022 from https://phys.org/news/2022-02-jila-atomic-clocks-einstein-relativity.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.