Studies of Atomic Hydrogen Contained in Solid Molecular Hydrogen Isotopes
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Non-technical Abstract The quantum mechanical phenomena of Bose Einstein Condensation leads to many fascinating and important effects. In 4He it leads to a superfluid where the liquid can flow with viscosity and transport heat without loss. In some metals it leads to superconductivity where electric currents are carried without loss - offering the potential for power distribution without the losses that occur in current power lines. BEC has also been observed in super-cooled atoms which could lead to more precise atomic clocks that power the global positioning system. Other, yet to be discovered systems, may show equally fascinating and important behavior. In this project we will attempt to produce a Bose Einstein Condensate in hydrogen atoms embedded in solid molecular hydrogen. The studies will take place at ultra-low temperature (below 0.1 degrees above absolute zero) and utilize microwave magnetic resonance techniques. This work will provide training in state-of-the-art low temperature and microwave techniques which are relevant in many areas of physics such as quantum computing. An active outreach program is pursued. Meetings with graduate students, visits by junior college students and participation in science fairs continues. For example, the principal investigator gives public lectures at the Texas A & M Physics and Engineering Festival with demonstrations. The festival is typically attended by more than 5000 students from all over the state of Texas and beyond. Technical Abstract The properties of hydrogen atoms embedded in solid molecular hydrogen films are studied by electron spin resonance in a high magnetic field (4.6 Tesla, resonant frequency 130 GHz) corresponding to 2mm waves. The spectrometer for these measurements is fully operational. A dilution refrigerator is now in place to cool the samples to temperatures below 100 mK. The large departure of the polarization of the nuclear spins from the Boltzmann distribution observed previously are investigated down to lower temperatures and at higher hydrogen atom concentrations in an attempt to reach full Bose-Einstein condensation. Although in previous experiments the spin-lattice relaxation was found to be several hours, it was not possible to fully saturate the transition between the two lowest hyperfine states. This anomalous behavior is fully investigated. Hole burning experiments in a magnetic field gradient also are performed to determine the hydrogen atom mobility as Bose-Einstein condensation occurs. Finally, the effect of different film substrates on the departure from Boltzmann statistics of hydrogen atoms are studied.
