Atomic Molecular and Optical physics (AMO) is a distinct subfield of physics traditionally concerned with exploring and understanding the physics of isolated few body sytems (atoms and molecules) using light as a tool for measurement. Although all fields are united within the domain of physics, AMO physics has traditionally been viewed as distinct from other subfields, each defined by the scope and content of its focus. AMO is distinct from particle or nuclear physics (concerned with the physics of sub-atomic paricles), biophysics (concerned with the physics of biologically relevant structures), soft and hard condensed matter physics (concerned with the physics of ‘condensed phase’ matter), cosmology and string theory (concerned with the physics of the space-time fabric itself and the origin of the physical laws), and astronomy (concerned with the physics of celestial bodies, including but not limited to plasma physics and aspects of nuclear physics and soft condensed matter physics). In the first half of the 20th century, much of our insight into quantum mechanics (including relativistic QM) was developed by the study of atomic and molecular systems.
Efforts within the field of AMO during the 20th century have produced major innovations in mankind’s ability to produce and manipulate coherent states of light and to produce and manipulate coherent states of atoms and molecules. The invention of the maser and laser has revolutionized not only the basic sciences (physics, chemistry, engineering, biology, medicine, etc…) but also society through the enabling of new technologies (in, for example, communication, data processing, measurement and detection, navigation, and materials processing). The invention of the laser also had revolutionary effects the domain of AMO physics. Suddenly it because possible to study non-linear optical physics and to study the quantum properties of light itself (quantum optics). Historically speaking, this is what turned atomic and molecular physics into AMO physics. Even in the absence of free charges and currents, Maxwell’s equations are incredibly rich, and the study of optics in the non-linear regime has yielded wonderfully exotic physical phenomena. In addition, it has enabled the production of non-classical states of light and the creation of a new class of ultra-broad band lasers which have revolutionized metrology by providing optical clockwork which spans and links the entire electro-magnetic spectrum from the radio frequency domain to the soft x-ray regime. Because of these advances, time is now the most accurately measured physical quantity and this provides the standard upon which all other precision measurements are built (where possible). Short pulsed lasers have also enabled a completely new domain of plasma physics and the direct study of extreme states of matter (e.g. matter at solid densities with energies of more than 1 eV per particle). Moreover, by the end of the 20th century, our exquisite control over light had translated into an ability to create and manipulate the quantum states of matter itself.
The creation of coherent and non-classical states of matter built from gas phase atomic and molecular ensembles has only recently been achieved (in the past decade) but has already made a significant impact on other fields of physics (most notably on condensed matter and nuclear physics) because of the connections (formal mathematical equivalence of the equations of motion) between these and other many-body quantum systems. As an illustration, a gas of ultra-cold, confined fermonic lithium atoms can behave in analogous ways to a confined electron gas in a solid, to a confined solid of interacting nucleons in a neutron star, or to a confined triplet of quarks inside a proton. Recently, it was observed by Stoof and co-workers that AMO physics provides us with the tools to actually make and study a supersymmetric string in the laboratory. Such connections are proving to be extremely fruitful in advancing our knowledge of fundamental physics across previously disparate domains of physics, and these new developments may eventually constitute a revolutionary advance even more profound than the invention of the laser.