• Scientists turn a hydrogen molecule into

    From ScienceDaily@1:317/3 to All on Fri Apr 22 22:30:48 2022
    Scientists turn a hydrogen molecule into a quantum sensor
    New technique enables precise measurement of electrostatic properties of materials

    Date:
    April 22, 2022
    Source:
    University of California - Irvine
    Summary:
    Using a scanning tunneling microscope equipped with a femtosecond
    terahertz laser, scientists have exploited the quantum properties of
    a two-atom hydrogen molecule to observe changes in the electrostatic
    field of a target sample, turning the hydrogen molecule into a
    quantum sensor.



    FULL STORY ========================================================================== Physicists at the University of California, Irvine have demonstrated
    the use of a hydrogen molecule as a quantum sensor in a terahertz laser-equipped scanning tunneling microscope, a technique that can
    measure the chemical properties of materials at unprecedented time and
    spatial resolutions.


    ==========================================================================
    This new technique can also be applied to analysis of two-dimensional
    materials which have the potential to play a role in advanced energy
    systems, electronics and quantum computers.

    Today in Science, the researchers in UCI's Department of Physics &
    Astronomy and Department of Chemistry describe how they positioned
    two bound atoms of hydrogen in between the silver tip of the STM and
    a sample composed of a flat copper surface arrayed with small islands
    of copper nitride. With pulses of the laser lasting trillionths of a
    second, the scientists were able to excite the hydrogen molecule and
    detect changes in its quantum states at cryogenic temperatures and in the ultrahigh vacuum environment of the instrument, rendering atomic-scale, time-lapsed images of the sample.

    "This project represents an advance in both the measurement technique
    and the scientific question the approach allowed us to explore,"
    said co-author Wilson Ho, Bren Professor of physics & astronomy and
    chemistry. "A quantum microscope that relies on probing the coherent superposition of states in a two-level system is much more sensitive
    than existing instruments that are not based on this quantum physics principle." Ho said the hydrogen molecule is an example of a two-level
    system because its orientation shifts between two positions, up and down
    and slightly horizontally tilted. Through a laser pulse, the scientists
    can coax the system to go from a ground state to an excited state in a
    cyclical fashion resulting in a superposition of the two states. The
    duration of the cyclic oscillations is vanishingly brief -- lasting
    mere tens of picoseconds -- but by measuring this "decoherence time"
    and the cyclic periods the scientists were able to see how the hydrogen molecule was interacting with its environment.

    "The hydrogen molecule became part of the quantum microscope in the
    sense that wherever the microscope scanned, the hydrogen was there in
    between the tip and the sample," said Ho. "It makes for an extremely
    sensitive probe, allowing us to see variations down to 0.1 angstrom. At
    this resolution, we could see how the charge distributions change on
    the sample." The space between the STM tip and the sample is almost unimaginably small, about six angstroms or 0.6 nanometers. The STM
    that Ho and his team assembled is equipped to detect minute electrical
    current flowing in this space and produce spectroscopic readings proving
    the presence of the hydrogen molecule and sample elements. Ho said this experiment represents the first demonstration of a chemically sensitive spectroscopy based on terahertz-induced rectification current through
    a single molecule.

    The ability to characterize materials at this level of detail based on hydrogen's quantum coherence can be of great use in the science and
    engineering of catalysts, since their functioning often depends on
    surface imperfections at the scale of single atoms, according to Ho.

    "As long as hydrogen can be adsorbed onto a material, in principle,
    you can use hydrogen as a sensor to characterize the material itself
    through observations of their electrostatic field distribution," said
    study lead author Likun Wang, UCI graduate student in physics & astronomy.

    Joining Ho and Wang on this project, which was supported by the
    U.S. Department of Energy Office of Basic Energy Sciences, was Yunpeng
    Xia, UCI graduate student in physics & astronomy.


    ========================================================================== Story Source: Materials provided by
    University_of_California_-_Irvine. Note: Content may be edited for style
    and length.


    ========================================================================== Related Multimedia:
    * Terahertz_laser-equipped_scanning_tunneling_microscope ========================================================================== Journal Reference:
    1. Likun Wang, Yunpeng Xia, W. Ho. Atomic-scale quantum sensing based
    on the
    ultrafast coherence of an H 2 molecule in an STM cavity. Science,
    2022; 376 (6591): 401 DOI: 10.1126/science.abn9220 ==========================================================================

    Link to news story: https://www.sciencedaily.com/releases/2022/04/220422131855.htm

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