The amplitude of the oscillations is determined by i and p and shows a maximum for some value of i and p = 60 to 90 microns. The lower frequencies show only an insignificant variation with i whereas in the highest frequency group there is a very rapid rise of frequency with current. The frequencies have a minimum value for p = 60 to 90 microns. The frequencies of the oscillations show a significant dependence on i and p and are independent of the circuit parameters. The existence of a common cut-off current for all these frequencies has been shown which is found to depend on the pressure in such a manner that it has a maximum value for p = 60 to 90 microns. Coherent oscillations were observed in the frequency range 40 to 100 kc/sec which were accompanied by three or four frequency groups in the range 170 to 2,300 kc/sec. Ho, 21 April 2022, Science.The phenomenon of electrical oscillations in the case of a d-c discharge in hydrogen in tho region of the positive v-i characteristic has been investigated for the pressure range 40 to 200 microns, discharge voltages 0.6 to 11.2 kv, and discharge currents 0.1 to 2.5 ma. Reference: “Atomic-scale quantum sensing based on the ultrafast coherence of an H 2 molecule in an STM cavity” by Likun Wang, Yunpeng Xia and W. Department of Energy Office of Basic Energy Sciences, was Yunpeng Xia, UCI graduate student in physics & astronomy. Joining Ho and Wang on this project, which was supported by the U.S. “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. 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. Ho said this experiment represents the first demonstration of a chemically sensitive spectroscopy based on terahertz-induced rectification current through a single molecule. ![]() 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. The space between the STM tip and the sample is almost unimaginably small, about six angstroms or 0.6 nanometers. At this resolution, we could see how the charge distributions change on the sample.” “It makes for an extremely sensitive probe, allowing us to see variations down to 0.1 angstrom. “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. ![]() student in physics & astronomy and Likun Wang and Ph.D. student in physics & astronomy Wilson Ho, Bren Professor of physics & astronomy and chemistry Yunpeng Xia, Ph.D. The UCI team responsible for the assembly and use of the terahertz laser-equipped scanning tunneling microscope pictured here are, from left to right, Dan Bai, UCI Ph.D. ![]() 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. 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. 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. “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.” “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, Donald Bren Professor of physics & astronomy and chemistry. “This project represents an advance in both the measurement technique and the scientific question the approach allowed us to explore,” says co-author Wilson Ho, UCI Donald Bren professor of physics & astronomy.
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