Ultracold molecules and chemistry near absolute zero

6 problems

• Which states produce Feshbach resonances in ultracold atom-molecule collisions?

  Partially resolved

  When ultracold atoms collide with ultracold molecules, the loss rate spikes at certain magnetic fields. Whether these spikes come from loosely bound long-range states or from the tangled short-range states of the three-atom complex is debated.

• First-principles lifetime of the four-atom collision complex

  Open

  When two molecules stick, the lifetime of the pair depends on how many internal states it can explore. Calculations of this count disagree with some measurements.

• Topological p-wave superfluid of fermionic polar molecules

  Open

  Fermionic molecules with dipoles, held apart by microwave shields, could pair into a superfluid with a built-in twist (p-wave) that hosts unusual edge states. Current gases are not yet cold enough.

• Can directly laser-cooled molecules reach quantum degeneracy?

  Open

  So far every ultracold molecular quantum gas was made by gluing together ultracold atoms. Molecules cooled directly with lasers, which include species useful for precision measurements, have not yet been cooled far enough to behave as a single quantum wave.

• When do ultracold reaction products depart from statistical theory?

  Partially resolved

  A reaction between two ultracold molecules produces new molecules in specific rotation states. Mostly the outcome looks random as statistics predicts, and the exceptions are not understood.

• Why do chemically stable ultracold molecules disappear in collisions?

  Partially resolved

  Even molecules that cannot react vanish from traps when they collide. They seem to stick together for a while and are then lost, but the full story is not settled.