Atoms are dependably uniform—you would have a hard time, for instance, telling one rubidium atom from another. Many atomic properties have been measured to extraordinary precision: The frequency of an electronic transition in a cesium atom, for ex- ample, is used to define the unit of time. With atoms being so well characterized, it is possible to use them as probes—to look for tiny changes in their properties stemming from interactions with other atoms or the environment. It helps if the atoms are extremely cold. When cooled to a fraction of a degree above absolute zero, atoms are easier to control, and their
quantum properties come to the fore. More than 20 years ago, scientists
cooled an atomic gas to the point where most of its atoms slumped to the
lowest energy state, forming a Bose-Einstein condensate (BEC). Now,
there are plans to send a small kit to the International Space Station, where
researchers can create a long-lasting BEC to study the nature of matter
and, possibly, gravity.
Back on Earth, physicists using the advanced tools of atomic and molecular physics have begun to address deep questions: What are the basic symmetries of the universe? Are fundamental constants actually constant? How
do interacting particles form matter? What happens to molecules in chemical reactions? Although there are more traditional approaches to answering
these questions—using particle accelerators, astrophysical observations,
numerical simulations, and tools of condensed matter physics and chemistry—the extreme tunability and relative simplicity of ultracold matter
experiments make them a compelling alternative.
Trapped in orbit p. 986
Probing the frontiers of particle
physics with tabletop-scale
experiments p. 990
Quantum simulations with ultracold
atoms in optical lattices p. 995
Cold molecules: Progress in quantum
engineering of chemistry and quantum
matter p. 1002
c RESEARCH ARTICLE BY P. PURI ET AL.
Artistic depiction of ultracold atoms (shown
with atomic orbitals) loaded into an optical
lattice. Blue and red respectively indicate
frozen and mobile states.