Speaker
Prof.
Cristophe Salomon
(Kastler Brossel, Paris, France)
Description
We will describe the present status for the realization of the SI unit of
time, the second. Microwave frequency standards operating with laser cooled
cesium and rubidium atoms have advanced by two orders of magnitude in the
last two decades. Cesium fountains currently operate at the fundamental
quantum noise limit with 107 detected atoms and display a relative
frequency stability of 1.5x10^-16 after 50 000 seconds of averaging time.
The SI second is realized with an accuracy of 3x10^-16 implying an error of
less than a second over 100 million years.
In a second part, we will describe tests of fundamental physical laws using
ultra-stable clocks. By comparing clocks of different nature new limits are
obtained for the time variation of the fundamental constants of physics
such as the fine structure constant alpha. The ability to compare microwave
and optical clocks using the newly developed frequency comb technique opens
a wide range of possibilities in clock comparisons.
By installing in space ultra-stable cold atom clocks (PHARAO/ACES project
for flight in 2013), improved tests of general relativity will be
performed, such as a measurement of Einstein’s gravitational red-shift at
the one part per million level. A new kind of relativistic geodesy based
on the Einstein effect will provide information on the Earth geoid. Finally
prospects for laser cooled atomic clocks operating in the optical domain
with frequency stability in the 10^-18 range will be outlined.
