This article presents a review of the current state of the art in the research field of cold and ultracold molecules. It serves as an introduction to the Special Issue of the New Journal of Physics on Cold and Ultracold Molecules and describes new prospects for fundamental research and technological development. Cold and ultracold molecules may revolutionize physical chemistry and few body physics, provide techniques for probing new states of quantum matter, allow for precision measurements of both fundamental and applied interest, and enable quantum simulations of condensed-matter phenomena. Ultracold molecules offer promising applications such as new platforms for quantum computing, precise control of molecular dynamics, nanolithography, and Bose-enhanced chemistry. The discussion is based on recent experimental and theoretical work and concludes with a summary of anticipated future directions and open questions in this rapidly expanding research field.
Deep Dive into Cold and Ultracold Molecules: Science, Technology, and Applications.
This article presents a review of the current state of the art in the research field of cold and ultracold molecules. It serves as an introduction to the Special Issue of the New Journal of Physics on Cold and Ultracold Molecules and describes new prospects for fundamental research and technological development. Cold and ultracold molecules may revolutionize physical chemistry and few body physics, provide techniques for probing new states of quantum matter, allow for precision measurements of both fundamental and applied interest, and enable quantum simulations of condensed-matter phenomena. Ultracold molecules offer promising applications such as new platforms for quantum computing, precise control of molecular dynamics, nanolithography, and Bose-enhanced chemistry. The discussion is based on recent experimental and theoretical work and concludes with a summary of anticipated future directions and open questions in this rapidly expanding research field.
and temperature (T ). Some technical approaches that are yet to be demonstrated in experiments can potentially address the important region of n ∼ 10 7 -10 10 cm -3 and T ∼ 1 mK -1 µK (the panel in the middle). (b) Applications of cold and ultracold molecules to various scientific explorations are shown with the required values of n and T . The various bounds shown here are not meant to be strictly applied, but rather they serve as general guidelines for the technical requirements necessary for specific scientific topics.
Scientific Goal 10 -17 -10 -14 10 6 -10 9 cm -3 < 1 K Tests of fundamental forces of nature 10 -14 > 10 9 cm -3 < 1 K Electric dipole interactions 10 -13 -10 -10 > 10 10 cm -3 < 1 K Cold controlled chemistry 10 -5
10 9 cm -3 < 1 µK Ultracold chemistry 1 > 10 13 cm -3 100 nK Quantum degeneracy with molecules 1 > 10 13 cm -3 100 nK Optical lattices of molecules 10 > 10 14 cm -3 < 100 nK Novel quantum phase transitions 100 > 10 14 cm -3 < 30 nK Dipolar crystals
Table 1. Orders of magnitude estimate of the phase space density and temperature of molecular ensembles required to achieve the main scientific goals that stimulate the development of ultracold molecule research. For dipolar physics, we assume a permanent dipole moment of 1 Debye. The molecular mass is assumed to be 100 amu.
Experimental work with molecular gases cooled to ultralow temperatures offers new insights into many body physics, quantum dynamics of complex systems, quantum chemistry, and fundamental forces in nature. From magnetic and electric decelerators to magneto-and photo-association to buffer gas cooling, a variety of newly developed experimental techniques provide new routes to physical discoveries based on cold and ultracold molecules. The research field of cold molecules brings together two of three main thrusts of modern atomic, molecular and optical (AMO) physics: the ultracold and the ultraprecise. It also brings together researchers from a variety of fields, including AMO physics, chemistry, quantum information science and quantum simulations, condensed matter physics, nuclear physics, and astrophysics. In order to explore exciting applications of cold matter experiments, it is necessary to produce large ensembles of molecules at temperatures below 1 Kelvin. We distinguish cold (1 mK -1 K) and ultracold (< 1 mK) temperature regimes. In this review article we give a broad overview of the state of the art in the research field of cold and ultracold molecules, describe the experimental methods developed to create molecular ensembles at extremely low temperatures, and discuss potential applications of cold and ultracold molecules anticipated in the near future. Our discussion focuses on the specific scientific goals that motivate most of the current experiments. These scientific goals are summarized in Table 1 and schematically depicted in Fig. 1.
Starting from a few research groups in the late 1990s working on the study of cold and ultracold molecules, the field has grown to encompass hundreds of researchers. This review is a part of and serves as an introduction to the Special Issue of the New Journal of Physics on Cold and Ultracold Molecules. The special issue contains 40 contributions, of which 38 are original research papers [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38], which give a snapshot of part of the current experimental and theoretical work in this research field, and two are reviews, including this article and an additional short review dedicated to time variation of fundamental constants [39].
The production of ultracold ensembles of atoms has revolutionized the field of AMO physics and generated much interest among researchers in other, traditionally disjoint fields. The impact of creating ultracold molecules is expected to be as large and profound as that made by the work performed with ultracold atoms. Molecules offer microscopic degrees of freedom absent in atomic gases. This gives ultracold molecular gases unique properties that may allow for the study of new physical phenomena and lead to discoveries, reaching far beyond the focus of traditional molecular science [40]. For example, a Bose-Einstein condensate (BEC) of polar molecules would represent a quantum fluid of strongly and anisotropically interacting particles and thereby greatly enhance the scope for study and applications of collective quantum phenomena. It could be used to elucidate the link between BECs in dilute gases and in dense liquids. The study of ultracold fermionic molecules is also of great interest: the electric dipoledipole interaction may give rise to a molecular superfluid via Bardeen-Cooper-Schrieffer (BCS) pairing. The dipole-dipole interaction is both long range and anisotropic and it leads to fundamentally new condensed-matter phases and new complex quantum dynamics. Ensembles of trapped polar molecules dressed by microwave fields may form topological
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