Millihertz-linewidth laser could make the best clocks more precise

A theoretical proposal by scientists at JILA (which is jointly operated by the National Institute of Standards and Technology and the University of Colorado, both in Boulder, CO) for a millihertz-linewidth laser could one day help improve the stability of the best clocks by two orders of magnitude—which would improve applications such as GPS, synchronization of data networks, and tests of the fundamental laws of physics, among others. The laser would emit light directly from an ultranarrow clock transition—avoiding thermal noise and producing a linewidth smaller even than the clock transition itself—by forcing an ensemble of atoms to emit energy collectively instead of individually.

To achieve this, ultracold alkaline-earth (such as strontium) atoms are placed in a high-Q cavity and confined by an external optical lattice so that they are all in phase with a specific cavity mode, creating a “macroscopic dipole.” So-called “repumping” lasers cool the atoms to the vibrational ground state and then pump them to provide inversion for the laser transition. While the resulting power would only by on the order of 10^-12 W, this would be enough to phase-lock a slave optical local oscillator, enabling stabilization of next-generation clocks. Contact Dominic Meiser at [email protected].