Ensembles of ultracold atoms suffer only minimally from thermal fluctuations and, accordingly, are useful in a variety of fields. A new laser-cooling technique is demonstrated that can be applied to simple, abundant atoms such as hydrogen and carbon.
Despite the prominent role of laser cooling in modern atomic physics, with applications ranging from quantum sensors to high-precision spectroscopy and ultracold chemistry, laser cooling techniques are still limited to atoms with simple energy level structure and closed transitions that are accessible by currently available continuous wave (cw) laser sources. Two main obstacles prevent the extension of laser cooling techniques to a variety of atomic species and molecules. The first is associated with technical difficulties in creating cw laser light in the vacuum ultraviolet (VUV) spectral range - the absence of those laser sources prevents laser cooling of simple atoms such as hydrogen, deuterium, and antihydrogen. The second obstacle is associated with complex energy level structure of many atoms and almost all molecules - it permits decay of an excited state into a number of lower-lying states that can be widely separated in energy, which makes laser cooling of such species inefficient and experimentally very challenging.
Ultracold atoms, produced by laser cooling and trapping, have led to recent advances in quantum information, quantum chemistry, and quantum sensors.A lack of ultraviolet narrow-band lasers precludes laser cooling of prevalent atoms such as hydrogen, carbon, oxygen, and nitrogen.Broadband pulsed lasers can produce high power in the ultraviolet, and we demonstrate that the entire spectrum of an optical frequency comb can cool atoms when used to drive a narrow two-photon transition.This multiphoton optical force is also used to make a magneto-optical trap.These techniques may provide a route to ultracold samples of nature's most abundant building blocks for studies of pure-state chemistry and precision measurement.
Laser cooling of atoms began more than 25 years ago and has led to spectacular advances in areas such as atomic clocks, Bose-Einstein condensation, degenerate Fermi gases, and ultracold collisions. Molecules, due to their complexity relative to atoms (1), have been slower to jump on the ultracold bandwagon but are now firmly on board. Three recent papers (2-4) describe techniques for efficiently and substantially reducing the vibrational motion of molecular ensembles, thus approaching the goal of large numbers of molecules that are cold in all their degrees of freedom, both external and internal.