Discrete Chromium

A NIST group can now supply chromium atoms on demand, one at a time, the first time such control over neutral atom delivery has been achieved.

At the microscopic level delivering electrons in a circuit or photons from a laser or atoms from a trap one at a time is more difficult than you would think. Precision control over motion is tricky enough but getting the objects to come one at a time, and not in twos, threes, or larger groups, is even harder.

Jabez McClelland and his colleagues send a tenuous beam of Cr atoms toward a magneto-optic trap. The atoms, which can be put into various excited states with a laser beam, announce their presence and their number by the photons they emit. If just one atom has come along, its emissions can be used to trigger a gate turning the loading of the trap on or off. In this way a single atom can be trapped by design, and at a rate of many atoms per second.

Extracting the atoms controllably, with gravity or with "optical tweezers," will be the final step in obtaining mastery over the single atoms. A deterministic source of single atoms is expected to be a critical component of various integrated atom-optic (atomtronics) schemes.

Why chromium atoms? Because Cr atoms have a magnetic moment 6 times larger than alkali atoms, making the trapping process much easier. The NIST group (jabez.mcclelland@nist.gov, 301-975-3721) will report its finding at an upcoming APS meeting (Division of Atomic, Molecular, and Optical Physics, DAMOP) in Williamsburg, Virginia May 28-June 1.