Chilled particles are close to zero

A two-step cooling process using lasers has allowed physicists to push molecules of calcium monofluoride down to a record low temperature, busting a barrier that until now has been impassable.

Decades ago, chilling individual atoms to near absolute zero opened a new world of research for particle physicists. This latest breakthrough could also provide fertile ground for learning more on how atoms behave when bound together as molecules.

A moving particle is a hot particle, meaning to cool down either an atom or a molecule you simply need to slow down its buzzing.

One way to do this is to take advantage of how atoms absorb and emit quanta of light, potentially losing some momentum in the process.

A laser tuned to a particular frequency is aimed at atoms trapped in a confined space by a magnetic field.

If the atom is moving away from the light, the frequency it experiences is Doppler shifted slightly towards the red end of the spectrum. If the particle is moving into the beam, the frequency hitting it shifts towards the blue end.

Getting that frequency right means atoms moving into the laser at a given velocity can absorb a photon of light. This bumps up one of its electrons to a new energy level, which then emits a photon in a random direction when it comes down.