The realization of superfluidity in a dilute gas of fermionic atoms, analogous to superconductivity in metals, represents a long-standing goal of ultracold gas research. In such a fermionic superfluid, it should be possible to adjust the interaction strength and tune the system continuously between two limits: a Bardeen–Cooper–Schrieffer (BCS)-type superfluid (involving correlated atom pairs in momentum space) and a Bose–Einstein condensate (BEC), in which spatially local pairs of atoms are bound together. This crossover between BCS-type superfluidity and the BEC limit has long been of theoretical interest, motivated in part by the discovery of high-temperature superconductors. In atomic Fermi gas experiments superfluidity has not yet been demonstrated; however, long-lived molecules consisting of locally paired fermions have been reversibly created. Here we report the direct observation of a molecular Bose–Einstein condensate created solely by adjusting the interaction strength in an ultracold Fermi gas of atoms. This state of matter represents one extreme of the predicted BCS–BEC continuum.

Emergence of a molecular Bose-Einstein condensate from a Fermi gas

Optofluidics - the synergistic integration of photonics and microfluidics - has recently emerged as a new analytical field that provides a number of unique characteristics for enhanced sensing performance and simplification of microsystems. In this review, we describe various optofluidic architectures developed in the past five years, emphasize the mechanisms by which optofluidics enhances bio/chemical analysis capabilities, including sensing and the precise control of biological micro/nanoparticles, and envision new research directions to which optofluidics leads.

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Optofluidic microsystems for chemical and biological analysis

We review the combinations of optical micro-manipulation with other techniques and their classical and emerging applications to non-contact optical separation and sorting of micro- and nanoparticle suspensions, compositional and structural analysis of specimens, and quantification of force interactions at the microscopic scale. The review aims at inspiring researchers, especially those working outside the optical micro-manipulation field, to find new and interesting applications of these methods.

Light at work: The use of optical forces for particle manipulation, sorting, and analysis

Certain molecules, it seems, may be laser cooled by methods technically similar to those applied with abundant success in atomic physics We discuss the spectroscopic criteria molecules should meet to make methods of Doppler cooling technically feasible and identify diatomic candidates Some candidates, such as the alkaline-earth monohydrides (eg BeH and CaH), are paramagnetic and amenable to magneto-optical trapping Our experimental study concentrates on CaH, and we present our recent high-resolution, molecular-beam-based measurements of low-J rotational lines within the A-X(0,0) band of CaH From these measurements we report hyperfine separations in the A-state, as important to laser-cooling spectroscopy, and centroidal transition frequencies for comparison with existing values We conclude with an outline of a possible magneto-optical trap for CaH

Laser-cooling molecules

Electromagnetic fluctuation-induced interactions known as van der Waals, Casimir, and Casimir-Polder forces are an active and exciting area of research. This review summarizes recent progress in this field with emphasis on theoretical and computational developments and their applications to materials including molecular structures, Dirac-like systems, optical metamaterials, composites with nontrivial boundary conditions, and biological matter.

Materials perspective on Casimir and van der Waals interactions

A cylindrical molecular lens is formed by focusing a nanosecond IR laser pulse. Trajectories of a ${\mathrm{CS}}_{2}$ molecular beam deflected by the lens are traced using the velocity map imaging technique. The characteristic lens parameters including the focal length, minimum beam width, and distance to the minimum-width position are determined. The laser intensity dependence of the parameters is in good agreement with theoretical predictions. Exciting possibilities for molecular optics and a new type of optical chromatography are opened up.

Molecular lens of the nonresonant dipole force

Quantum reflection allows an atom or molecule to be reflected from a solid before it reaches the region where it would encounter the repulsive potential of the surface. We observed nondestructive scattering of the helium dimer (He(2)), which has a binding energy of 10(-7) electron volt, from a solid reflection grating. We scattered a beam containing the dimer as well as atomic helium and larger clusters, but could differentiate the dimer by its diffraction angle. Helium dimers are quantum reflected tens of nanometers above the surface, where the surface-induced forces are too weak to dissociate the fragile bond.

https://science.sciencemag.org/content/sci/331/6019/892.full.pdf

Quantum reflection of He2 several nanometers above a grating surface.

We observe high-resolution diffraction patterns of a thermal-energy helium atom beam reflected from a microstructured surface grating at grazing incidence. The grating consists of $10\text{\ensuremath{-}}\ensuremath{\mu}\mathrm{m}$-wide Cr strips patterned on a quartz substrate and has a periodicity of $20\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}$. Fully resolved diffraction peaks up to the seventh order are observed at grazing angles up to $20\phantom{\rule{0.3em}{0ex}}\mathrm{mrad}$. With changes in de Broglie wavelength or grazing angle the relative diffraction intensities show significant variations which shed light on the nature of the atom-surface interaction potential. The observations are explained in terms of quantum reflection at the long-range attractive Casimir--van der Waals potential.

https://pure.mpg.de/pubman/item/item_736689_3/component/file_736688/367185.pdf

Quantum reflection of helium atom beams from a microstructured grating

A molecular lens of the nonresonant dipole force formed by focusing a nanosecond IR laser pulse has been applied to benzene and CS2 molecular beams Using the velocity map imaging technique for molecular ray tracing, characteristic molecular lens parameters including the focal length (f ), minimum beam width (W), and distance to the minimum beam width position (D) were determined The laser intensity dependence of the observed lens parameters was in good agreement with theoretical predictions W was independent of the laser peak intensity (I0), whereas f and D varied linearly with 1/I0 The differences in lens parameters between the molecular species were well correlated with the polarizability per mass values of the molecules A high chromatographic resolution of Rs=084 was achieved between the images of benzene molecular beams undeflected and deflected by the lens The possibilities for a new type of chromatography are discussed

Bum Suk Zhao

Papers

Molecular lens of the nonresonant dipole force

Quantum reflection of He2 several nanometers above a grating surface.

Quantum reflection of helium atom beams from a microstructured grating

Molecular lens applied to benzene and carbon disulfide molecular beams

Separations based on the mechanical forces of light.