Technical Activities

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"Technical Activities 2004" - Table of Contents

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Electron and Optical Physics Division
The strategy for meeting this goal is to improve measurement science and to develop the measurements and standards needed by emerging science and technology-intensive industries.

GOAL: To support
emerging electronic,
optical, and nanoscale
technologies.

Strategic Focus Areas:

   

First

Nanoscale Electronics and Magnetics - to develop techniques for fabricating nanostructures and measuring their electronic and magnetic properties.

Second   

Extreme Ultraviolet Radiation Metrology - the development of metrology for extreme-ultraviolet (EUV) optics, the maintenance of national primary standards for radiometry in the EUV and adjoining spectral regions, and the operation of national user facilities for EUV science and applications.

Third

Coherent Matter-Wave and Quantum Information Processing Metrology - the development of ultracold atom technology, in particular the use of coherent matter waves in sensors, atom interferometers, and quantum information processing devices.

Coherent Matter-Wave and Quantum Information Processing Metrology

INTENDED OUTCOME AND BACKGROUND

This program provides measurements and data to enable the development of ultracold atom technology, in particular the use of coherent matter waves in sensors, atom interferometers, and quantum information processing devices.

The Division maintains two efforts in this area, one theoretical and one experimental. The theoretical program is focused on quantitative modeling of degenerate quantum gases, with particular attention to the dynamics of Bose-Einstein condensates subject to external forces, e.g., manipulation of condensates confined in an optical lattice. This program is an outgrowth of extensive collaborations with experimental groups at NIST, JILA, and elsewhere, begun in the mid-1990s.

The experimental program develops deterministic atom-delivery systems, i.e., devices that can deliver precisely one atom to a predetermined location, on demand. In addition, the Division is developing a testbed for quantum communication systems, together with the Atomic Physics Division and the Information Technology Laboratory.

Accomplishments

  • Characterization of “Atom-on-Demand” Source

    Recent developments in our laboratory have led to a new source of atoms that is almost completely deterministic: single atoms can be made available at a high rate with near unity certainty. Such a source has applications not only in quantum information processing, where single atoms can be used as qubits, but also in nanotechnology, when doping of nanostructures reaches the level where each nanostructure contains only a countable number of dopants.

    In order to proceed to the next step in our research program, which will be to extract atoms from our source and demonstrate controlled deposition, we have conducted a number of studies to characterize our source. These have involved a detailed analysis of all the experimental parameters that determine the performance of the source, and also real-time photography of single atoms.

    The detailed analysis has allowed us to implement Monte Carlo simulations that show extremely good agreement with experimental observations of such parameters as the single-atom probability and the single-atom extraction success rate. The photography, using a high-sensitivity CCD camera (Fig. 9), has given us the ability to investigate the spatial properties of our source, which will prove crucial in extracting, transporting, and depositing the single atoms with high spatial resolution.

    Figure 9

    Figure 9. Real-time images of single atoms in an atom-on-demand source. Without feedback, the number of atoms is random, fluctuating between one, two, and three. With feedback, there is always just a single atom in the source.


    CONTACT: Dr. Jabez J. McClelland
    (301) 975-3721
    jabez.mcclelland@nist.gov


  • Resonant Atom-Molecule Mixtures in Quantum-Degenerate Gases

    Cooling fermionic, atomic gases to quantum degeneracy, in conjunction with the ability to directly control the interatomic interactions through magnetic-field-tunable Feshbach resonances, has opened the door to a detailed study of the crossover between Bardeen-Cooper-Schrieffer superfluidity and Bose-Einstein condensation of diatomic molecules in an atomic Fermi gas.

    A Feshbach resonance can be used to couple atom pairs into a bound molecular state, thereby creating bosonic dimers in the gas. Under suitable conditions, these dimers can undergo Bose-Einstein condensation. The BCS-BEC crossover is a cornerstone problem of condensed matter physics, due in large part to its importance in the understanding of high-temperature superconductivity.

    We have studied the equilibrium phase diagram of atom-molecule mixtures in a simple model under experimentally relevant conditions. A finite fraction of molecules persists for energies above dissociation threshold. At high temperatures this is ascribable to a detailed balance between atomic association and molecular dissociation in the gas, while in the quantum-degenerate regime Pauli blocking stabilizes molecular states embedded in the continuum.

    Figure 10

    Figure 10. Phase diagrams of atom-molecule mixture showing the molecule fraction (A) and condensate fraction (B) as a function of temperature and resonance energy, εRes, in units of the Fermi temperature and Fermi energy, respectively. Lines indicate contours of constant entropy, which are the trajectories followed by the system under adiabatic variation of the threshold energy.

    Recent experiments found a significant discrepancy between theory and experiment concerning the dependence of the dimer condensation threshold on the temperature of the gas. We found that this discrepancy disappeared when the thermodynamic evolution of the system was taken into account. In particular, the temperatures measured in the experiments are those of the initial state of the Fermi gas; as one sweeps through the Feshbach resonance, the temperature of the gas changes. The conditions of the experiments are believed to be adiabatic, which means that the system should follow a trajectory of constant entropy in the thermodynamic phase diagram. Examples of such trajectories are shown in Fig. 10. These demonstrate that assuming fixed temperature of the gas would overestimate the condensate threshold temperature.


    CONTACT: Dr. Charles W. Clark
    (301) 975-3708
    charles.clark@nist.gov


First strategic focus   |   Second strategic focus   |   Third strategic focus

"Technical Activities 2004" - Table of Contents