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Comptes Rendus Physique

Historical foreword: Jean Dalibard, the magneto-optical trap, and the ascent of physics with cold atomic gases

William D. Phillips

Published Feb 2, 2024• 0 citations
Publisher

Abstract

I present my personal perspective on the importance of the invention by Jean Dalibard of the magneto-optical trap (MOT), which has for many years been the “workhorse” of the field of laser cooling and cold atomic gases. I recount some of the history related to the MOT and argue that its invention enabled cold atomic gases to become the dominant part of Atomic, Molecular, and Optical (AMO) physics that it is today.

DOI
10.5802/crphys.172

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I present my personal perspective on the importance of the invention by Jean Dalibard of the magneto-optical trap (MOT), which has for many years been the “workhorse” of the field of laser cooling and cold atomic gases. I recount some of the history related to the MOT and argue that its invention enabled cold atomic gases to become the dominant part of Atomic, Molecular, and Optical (AMO) physics that it is today.
Abstract The extension of laser cooling and trapping techniques from atoms to molecules is currently the subject of intense and growing interest. Molecular laser cooling and trapping offers a general technique applicable to a variety of molecules with different properties and internal structures and is well-suited to the growing list of proposed applications for ultracold molecules. The recent development of optical cycling schemes for specific molecular species now allow each molecule to scatter up to ∼10 6 photons. This has proven sufficient for multiple groups to laser cool and slow molecular beams and, notably, capture molecules in magneto-optical traps (MOTs) and cool them to ultracold temperatures. MOTs are the workhorse technique for atomic physics in the ultracold regime and today’s molecular MOTs represent a powerful starting point for the study and manipulation of ultracold molecular gases. This Topical Review presents a summary of the progress made in this new and emerging field.
While cold molecule experiments are rapidly moving towards their promised benefits of precision spectroscopy, controllable chemistry, and novel condensed phases, heretofore the field has been greatly limited by a lack of methods to cool and compress chemically diverse species to temperatures below ten millikelvin. While in atomic physics these needs are fulfilled by laser cooling, magneto-optical trapping, and evaporative cooling, until now none of these techniques have been applicable to molecules. In this thesis, two major breakthroughs are reported. The first is the observation of evaporative cooling in magnetically trapped hydroxyl (OH) radicals, which potentially opens a path all the way to Bose-Einstein condensation of dipolar radicals, as well as allowing cold- and ultracold-chemistry studies of fundamental reaction mechanisms. Through the combination of an extremely high gradient magnetic quadrupole trap and the use of the OH Λ-doublet transition to enable highly selective forced evaporation, cooling by an order of magnitude in temperature was achieved and yielded a final temperature no higher than 5mK. The second breakthrough is the successful application of laser cooling and magneto-optical trapping to molecules. Motivated by a proposal in this thesis, laser cooling of molecules is now known to be technically feasible in a select but substantial pool of diatomic molecules. The demonstration of not only Doppler cooling but also two-dimensional magneto-optical trapping in yttrium (II) oxide, YO, is expected to enable rapid growth in the availability of ultracold molecules--just as the invention of the atomic magneto-optical trap stimulated atomic physics twenty-five years ago.
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The advent of the magneto-optical trap (MOT) introduced to the field of atomic physics an unprecedented surge in research opportunities and the potential for widespread application in relating fields, such as those of quantum computation, quantum optics, laser physics, and plasma physics. The MOT makes use of a process called laser cooling, whereby atoms can be manipulated through the absorption and emission of photons, in conjunction with inhomogeneous magnetic fields, to cool atoms to kinetic temperatures as low as 200 µK and contain them in a region of space. This process has given researchers a remarkable level of control and has provided the means for extensive
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