  Atoms made of a particle and an antiparticle are unstable, usually surviving
less than a microsecond. Antihydrogen, made entirely of antiparticles, is
believed to be stable, and it is this longevity that holds the promise of
precision studies of matter-antimatter symmetry. We have recently demonstrated
trapping of antihydrogen atoms by releasing them after a confinement time of
172 ms. A critical question for future studies is: how long can anti-atoms be
trapped? Here we report the observation of anti-atom confinement for 1000 s,
extending our earlier results by nearly four orders of magnitude. Our
calculations indicate that most of the trapped anti-atoms reach the ground
state. Further, we report the first measurement of the energy distribution of
trapped antihydrogen which, coupled with detailed comparisons with simulations,
provides a key tool for the systematic investigation of trapping dynamics.
These advances open up a range of experimental possibilities, including
precision studies of CPT symmetry and cooling to temperatures where
gravitational effects could become apparent.
