US physicists have successfully trapped and cooled molecules below 1 Kelvin for the first time. Previously only atoms had been cooled to such temperatures. John Doyle and colleagues from Harvard University in the US hope to use the new trapping technique to study ultracold collisions and superfluid behaviour in molecular gases (Nature 395 148).
Many of the optical and magnetic techniques used to trap and cool atoms do not work with molecules because they have complex internal energy levels. Instead Doyle and his colleagues chilled the molecules by cooling the walls of a container filled with a mixture of helium atoms and calcium monohydride molecules. The molecules were cooled as a result of collisions with the atoms. The Harvard team then applied a magnetic field to push the molecules to the centre of the chamber. The most energetic molecules escaped the field but over 100 million remained trapped in the centre at a temperature of 400 mK ± 50 mK for as long as two seconds. Doyle now hopes to improve the design of the trap to increase the confinement time. He also plans to remove the helium atoms from the chamber using a vacuum pump, which will further reduce the temperature of the molecules through the process of evaporative cooling.
