Research Bits: Nov. 1

Rare earth atomic level manipulation; light compression; frequency comb improvement.


Atomic-level rare earth manipulation

Scientists from Ohio University, Argonne National Laboratory, and the University of Illinois at Chicago have rotated a single, charged rare earth molecule on a metal surface without changing the charge.

The team used scanning tunneling microscopy (STM) system to rotate a positively charged Europium base molecule with negatively charged counterions as a pivot point on a gold surface. The experiment requires that a 2 nm molecule is kept at degrees K (-450 degrees Fahrenheit) in an ultrahigh vacuum. The teams tried the experiment in two different labs to be sure it was reproducible.

“Rare earth elements are vital for high-technological applications including cell phones, HDTVs, and more. This is the first-time formation of rare-earth complexes with positive and negative charges on a metal surface and also the first-time demonstration of atomic-level control over their rotation,” said team lead Saw-Wai Hla, who is a scientist at Argonne and professor of physics and astronomy in the College of Arts and Sciences at Ohio University.

The U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Science and Engineering Division funded the research.

Compressing light

A nanostructure that forms a dielectric nanocavity can compress light, as found by researchers from Technical University of Denmark (DTU).

The DTU researchers designed a dielectric nanocavity made of silicon that concentrates light in a volume 12 times below the diffraction limit. Other forms of nanocavities have been tried in the past but the researchers kept yield in mind and used dielectric bowtie cavities (DBCs) with the DTU team’s special sauce — topology optimization of  compact silicon nanocavity. “There is no doubt that this is an important step to developing a more energy-efficient technology for, e.g., nanolasers for optical connections in data centers and future computers — but there is still a long way to go,” said Marcus Albrechtsen, DTU Electro PhD-student and first author on the research, to Science Direct. The team’s research has just been published in Nature Communications.

Frequency comb improvement measures light

Scientists at the National Institute of Standards and Technology (NIST) found a new way to use a frequency comb to measure light pulse arrival times with greater sensitivity, under a broader set of conditions. The NIST team created a time-programmable frequency comb, in which they manipulated the timing of the pulses using a digital controller to adjust the time output of two frequency combs so that one of the comb’s pulses always overlaps with the returning pulses from the target. The advantage is it makes good use of available photons, eliminates dead time, and no information is lost.

“We’ve essentially broken this rule of frequency combs that demands they use a fixed pulse spacing for precision operation,” said Laura Sinclair, a physicist at NIST’s Boulder campus and one of the paper’s authors. “By changing how we control frequency combs, we have gotten rid of the trade-offs we had to make, so now we can get high-precision results even if our system only has a little light to work with.”

The new frequency comb arrangement used around 0.02% of the photons needed previously.

NIST frequency comb improvement

Fig. 1: A example showing how the distance measurement using dual frequency combs requires tight coordination between the pulse timing of the two combs. See NIST’s website for a moving version of the graphic.

Some of the potential uses for the frequency comb techniques may be precise formation flying of satellites for coordinated sensing of Earth or space, improving GPS, and supporting other ultra-precise navigation and timing applications, according to the NIST press release.

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