Atoms Made Entirely of Antimatter: Two Methods Produced Slow Antihydrogen Gerald Gabrielse , Leverett Professor of Physics, Harvard University, Spokesperson for the ATRAP Collaboration

An antihydrogen atom -- a positron in orbit about an antiproton -- is the simplest atom made entirely of antimatter. Producing antihydrogen atoms that are cold enough to be trapped for precise laser spectroscopy, to allow the comparison of antihydrogen and hydrogen, is a goal we set many years ago. Steady progress started with demonstrating techniques to accumulate cold antiprotons, and continued with the demonstration of crucial devices -- like the nested Penning trap developed to bring slow antiprotons and positrons together. Several exciting years have now seen the first production, observations and studies of slow antihydrogen atoms. So far we have developed and demonstrated two production methods. 1. Slow antihydrogen is formed during positron cooling of antiprotons in a nested Penning trap, and such atoms have been observed with two different detection techniques. Field ionization detection of these atoms makes it possible to go beyond simply counting their number -- to probe their internal structure and measure their velocity. The atoms identified so far are in highly excited states and still travel much too rapidly to trap. The new techniques to probe the internal state and speed are the necessary first steps towards developing methods to attain ground state antihydrogen atoms that are much colder. 2. Lasers control the production of antihydrogen atoms via charge exchange collisions -- a method that seems to naturally produce antihydrogen atoms with essentially the low energy distribution of the antiprotons from which they form.