> <i>But characterizing the clocks this well meant that the ytterbium clocks could detect how Earth’s gravity had slowed time, accurately determining their location in the Earth’s gravitational field to within a centimeter. </i><p>This is amazing to me. There was an article published 4 or so years ago that predicted a satellite network of quantum entangled clocks that would yield similar resolution throughout the entire volume of the earth.<p>Essentially, such an ultra-GPS constellation would be able to determine the density of any centimeter-sized volume anywhere within the earth. It's nice to see regular progress to such a goal.