John F. Clauser

Bell's theorem: Experimental tests and implications

Bells theorem represents a significant advance in understanding the conceptual foundations of quantum mechanics. The theorem shows that essentially all local theories of natural phenomena that are formulated within the framework of realism may be tested using a single experimental arrangement. Moreover, the predictions by those theories must significantly differ from those by quantum mechanics. Experimental results evidently refute the theorems predictions for these theories and favour those of quantum mechanics. The conclusions are philosophically startling: either one must totally abandon the realistic philosophy of most working scientists, or dramatically revise out concept of space-time.

Generalized Talbot-Lau Atom Interferometry

Publisher Summary This chapter describes a particular form of a grating interferometer called the generalized Talbot-Lau (GTL) interferometer. The chapter first identifies a significant weakness (low throughput) of its progenitor form, separated beam envelope (SBE) interferometry, outlines the operating principles of the GTL interferometry, and shows how GTL interferometry remedies this weakness. The GTL interferometry is based on a unique form of interference intimately associated with Fresnel diffraction that occurs when Fraunhofer diffraction orders overlap. This effect was originally discovered in the optical domain using lenses and gratings, and is called the Talbot effect. Its diffraction pattern consists of the so-called Fourier and Fresnel fringes that, surprisingly, are actually multiply “aliased” near self-images of a gratings periodic complex amplitude transmission function. The chapter introduces the Talbot effect and gives a brief historical outline of work contributing to its understanding. It also introduces the related Lau effect and the Talbot interferometer. The chapter also shows how these can be combined to create generalized lens-free Talbot-Lau interferometers, suitable for de Broglie wave interferometry.

Results of Atom Interferometry Experiments with Potassium

Results of high flux atom interferometry experiments with potassium in generalized Talbot-Lou configurations are presented. The interferometer consists of a sequence of three planar vacuum-slit diffraction gratings, microfabricated from silicon nitride membranes. Interference fringes are sensed by measuring the transmission of atoms on a hot-wire as a function of grating relative position. Different spatial Fourier components in the diffraction pattern are resonant in the interferometer at different atomic velocities. When a laser cooled slow beam is incident, various different diffraction patterns are observed as a function of atomic velocity, selected via the tuning of cooling lasers. In an alternative “Heisenberg Microscope” configuration an incident thermal beam produces a velocity average over different fringe patterns that averages over and washes out the high frequency Fourier components. In this configuration AC modulated laser light passes through the interferometer. Via the Doppler shift, it is scattered only by atoms in a narrow velocity band. Since imaging of the fluorescent light could determine which slit an atom passes, the laser destroys, and thereby reveals via the AC modulation, the associated high-frequency fringe contribution.