A molecular fountain

TL;DR

This paper introduces the first molecular fountain, enabling extremely long interrogation times for molecules, which enhances precision in spectroscopic measurements and tests of fundamental physics.

Contribution

It demonstrates the creation of a molecular fountain with long free-fall times, allowing for ultra-precise measurements and new experimental possibilities in molecular physics.

Findings

Molecules are decelerated, cooled, and launched with controlled velocities.

Molecules can be observed in free fall for up to 266 milliseconds.

The setup achieves very low transverse and longitudinal temperatures.

Abstract

The resolution of any spectroscopic or interferometric experiment is ultimately limited by the total time a particle is interrogated. We here demonstrate the first molecular fountain, a development which permits hitherto unattainably long interrogation times with molecules. In our experiments, ammonia molecules are decelerated and cooled using electric fields, launched upwards with a velocity between 1.4 and 1.9\,m/s and observed as they fall back under gravity. A combination of quadrupole lenses and bunching elements is used to shape the beam such that it has a large position spread and a small velocity spread (corresponding to a transverse temperature of $<$10\,$\mu$K and a longitudinal temperature of $<$1\,$\mu$K) when the molecules are in free fall, while being strongly focused at the detection region. The molecules are in free fall for up to 266\,milliseconds, making it possible to perform sub-Hz measurements in molecular systems and paving the way for stringent tests of fundamental physics theories.