Cold atom research group led by Prof. ZHAN Mingsheng at Wuhan Institute of Physics and Mathematics of the Chinese Academy of Sciences has achieved an important experimental progress of trapping a single rubidium atom in a blue detuned optical bottle beam trap.

Trapped single neutral atoms are good candidate blocks for building a quantum computer besides trapped ions, quantum dots, etc. Most groups choose to trap single atoms with the red detuned trap (bright trap). But the dark trap has several advantages over the bright trap. As the atoms are trapped in the “dark” place, the photon scattering rate due to the trapping laser can be greatly reduced, while in the bright trap this rate can be reduced only by increasing the detuning of the trapping laser. The coherent time of the atoms in a dark trap can thus be maintained to several seconds. The ac Stark shift of the trapping laser can also be eliminated in the dark trap.

The group members XU Peng and HE Xiaodong used a spatial light modulator to generate a strongly focused blue detuned optical bottle beam. Single atoms were efficiently loaded from a magneto-optical trap and stored in the optical trap for several seconds. They also compressed the trapping volume to the collisional regime, in which more than one atom could not be stably trapped.

This result is published in Optics Letters (Vol. 35, No. 13 / July 1, 2010).