One Hundred Years of Quantum Physics Kleppner, Daniel; Jackiw, Roman
Science (American Association for the Advancement of Science),
08/2000, Letnik:
289, Številka:
5481
Journal Article
Recenzirano
This year marks the 100th anniversary of Max Planck's creation of the quantum concept, an idea so revolutionary that it took nearly 30 years for scientists to develop it into the theory that has ...transformed the way scientists view reality. In this month's essay, Daniel Kleppner and Roman Jackiw recount how quantum theory, which they rate as "the most precisely tested and most successful theory in the history of science," came to be, how it changed the world, and how it might continue to evolve to make the dream of ultimate understanding of the universe come true.
A new path to ultracold hydrogen deCarvalho, R; Brahms, N; Newman, B ...
Canadian journal of physics,
04/2005, Letnik:
83, Številka:
4
Journal Article
Recenzirano
Ultracold hydrogen offers unique possibilities for precision spectroscopy, studies of atomic interactions, and the creation of quantum fluids containing mixtures of hydrogen and deuterium. Current ...techniques for trapping and cooling hydrogen have produced large condensates with N ∼ 10
9
atoms, but suffer from a variety of experimental limitations. Among these are the slow evaporative cooling rate due to the small HH elastic-scattering cross section, the need for a superfluid helium film in the initial thermalization process, a geometry that severely limits detection efficiency, and the inability to trap deuterium. We are constructing a new apparatus based on buffer-gas cooling that will overcome these problems. To accelerate evaporative cooling, the thermalization rate is increased by simultaneously loading lithium and hydrogen into a 4.2 T anti-Helmholtz trap. Lithium accelerates evaporative cooling because the LiH elastic-scattering cross section is ∼1200 times larger than that of HH. Hydrogen and lithium will be produced by laser ablation of solid LiH in a
3
He buffer gas held at temperatures of ∼350 mK. Because no wall collisions are needed for initial thermalization, ablating a solid sample of LiD should enable studies of deuterium. The apparatus is in the final stages of construction. We report on results of initial tests and discuss the new scientific opportunities made possible by this approach.PACS No.: 32.80.Pj
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The addition of atomic hydrogen to the set of gases in which Bose–Einstein condensation can be observed expands the range of parameters over which this remarkable phenomenon can be studied. Hydrogen, ...with the lowest atomic mass, has the highest transition temperature,
50
μK
in our experiments. The very weak interaction between the atoms results in a high ratio of the condensate to normal gas densities, even at modest condensate fractions. Using cryogenic rather than laser precooling generates large condensates. Finally, two-photon spectroscopy is introduced as a versatile probe of the phase transition: condensation in real space is manifested by the appearance of a high-density component in the gas, condensation in momentum space is readily apparent in the momentum distribution, and the phase transition line can be delineated by following the evolution of the density of the normal component.
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