Cooling atoms — Clocks and inertial sensors

Since the 1980s, the field of laser cooling of atoms has taken on considerable importance and, in addition to the Nobel Prize awarded in 1998 to C. Cohen-Tannoudji, W. Phillips and S. Chu, a new field was born: atomic optics and interferometry. As early as 1990, a large number of first-principles experiments began to appear, demonstrating that atomic optics was a reality with great potential, both for fundamental physics and for applications.

In particular, in addition to cold atomic clocks, two other fields of application seemed particularly promising. On the one hand, a large number of laboratories were working on the basic elements of atom optics, with a special mention for atom mirrors and diffractive structures (see special issues devoted to this theme, such as "Journal of the Optical Society of America B" [1] or "Special Issue on Atom Optics of Appl. Phys. B" [2] , which offers a compendium of publications from the world's leading research groups). The ability to direct and, above all, focus a beam of atoms opened the way to a potentially spectacular application: atomic lithography. In this particular field, the idea was to use an optical interference pattern to exert highly localized forces on the atoms and thus reproduce the optical pattern on the atomic beam.

The particular field of atom interferometry has also evolved rapidly. After the first demonstrations, the field turned to the exploration of new types of interferometers. The extreme sensitivity of these devices made it possible to use interferometers to highlight spectroscopic effects, effects specific to the evolution of matter waves, or the measurement of fundamental constants.

But it's another application that holds great promise for the future: atomic inertial sensors [3] .

Another important event revolutionized the field of atomic optics and interferometry. The year 1995 saw the successful realization of Bose-Einstein condensates from dilute gas, celebrated by the Nobel Prize awarded to E. Cornell, W. Ketterle and C. Weiman in 2001. Such a condensate is obtained when a cloud of low-density bosons is cooled to a temperature such that the thermal De Broglie wavelength is of the order of the interatomic distance. In such a state, all atoms are in the same quantum mode (such a phenomenon had already been observed in superfluids and superconductors, but never in dilute gases). Today's atomic interferometers can therefore use a coherent source of atomic waves, analogous to a laser, which is a coherent source of electromagnetic waves [4]...