Les molécules les plus froides du monde à l'Université de Yale

Selon un article publié dans le journal Nature, des physiciens de l'Université de Yale ont obtenu les molécules les plus froides jamais obtenues par refroidissement direct.
According to a research article published in the journal Nature, physicists at Yale University have achieved the coldest ever molecules through direct cooling. The strontium monofluoride (SrF) molecules dropped to 2.5 millikelvin (2.5 thousandths of a degree above absolute zero) through a laser cooling and isolating process called magneto-optical trapping (MOT).

This represents a landmark in physics, offering chances to learn about fundamental chemical mechanisms and opening the door for further experimentation from precision measurement and quantum simulation to ultracold chemistry and tests of the standard model of particle physics.

Magneto-optical trapping, was widely used among atomic physics in the past generation, but only at single-atom level. The technology uses laser beams to simultaneously cool particles and hold them in place.
Until recently, this trapping proved impossible because of complicated vibrations and molecule rotations.
It was finally achieved using pulses of SrF shooting out from a cryogenic chamber to form a beam of molecules, which is then slowed by pushes from a laser beam, “like trying to slow down a bowling ball with ping pong balls” as Yale Professor Dave DeMille explains: “you have to do it fast and do it a lot of times”.
The slowed molecules enter a specially-shaped magnetic field, where opposing laser beams pass through the center of the field, along three perpendicular axes, and become trapped. This allows “to both cool things down and apply force that leaves the molecules levitating in an almost perfect vacuum”, says DeMille.

SrF was chosen for its structural simplicity: it has effectively just one electron orbiting around the whole molecule.