Quantum computers of the future may rifle through calculations
by altering the quantum states of scores of atoms confined
within clever traps. However, atomic physicists must first learn
how to place a few neutral atoms into such traps and control
their tendencies to escape or randomly change their quantum
states during the manipulation. In the 30 October PRL, German
researchers report that they successfully transferred an exactly
known number of cesium atoms from a trap that uses lasers and
magnetic fields into a calmer snare that uses only a single
laser beam. The technique holds promise as a source of one well-
behaved atom at a time. Both traps are popular tools for atomic
physicists. The first, called a magneto-optical trap, or MOT,
relies on radiation pressure from several laser beams to confine
atoms within a magnetic field. Atoms absorb photons from the
lasers and then re-emit photons in random directions. This
process slows the atoms until they settle in a cold knot at the
center of the magnetic field