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)
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 (firstname.lastname@example.org, 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.