The CalciumClock project
Robust clocks for application outside the lab
The world’s finest optical clocks reach a stunning fractional uncertainty in the 10-19 range: they would be off by less than a millisecond when operated over the age of the Universe. Equally impressive, they are sensitive to the gravitational redshift in the Earth’s gravitational field that corresponds to a height difference of about 1 cm.
The usage of these dedicated optical clocks with a performance in the 10-19 range is certainly limited to very few metrology labs. For industrial applications (e.g. timekeeping or synchronization of networks), a performance comparable to hydrogen masers (fractional uncertainty in the 10-16 range) would be sufficient.
In this project, we aim to develop rugged and small optical clocks with an uncertainty in the 10-16 range, to be employed outside a quantum optics laboratory. A number of such clocks will be connected via the existing telecom infrastructure to form a network of phase-stabilized network nodes.
We chose beam clocks of alkaline-earth metal atoms as the platform for our devices. Such clocks, using calcium as the atomic species (linewidth 370 Hz) have been pioneered by the NIST group, and we will follow their footsteps. To test their performance, we will put one of these clocks into an elevator: based purely on the gravitational redshift, we will use the reading of the clock to tell at which floor the elevator is.
The transition wavelength in calcium is at 657 nm, far away from the infra-red wavelength used in telecommunication. We will use wavelength conversion in nonlinear crystals to convert light at infra-red wavelength to the visible wavelength range.
On this project, we cooperate with the Max Planck Institute for Radio Astronomy (MPIfR) to explore the suitability of these clocks for the synchronization of arrays of radio telescopes, as well as with the geodesy people from the University of Bonn. The development of such clocks is perfectly aligned with the current Quantum Flagship initiative of the European Union.