Research Bits: Nov. 29

More accurate GPS alternative; traveling phonons transmit, store more qubits; whirlpool magnetic memory — skyrmions found more efficient.


Earth-bound, more accurate GPS

A new idea for terrestrial-based global navigation satellite systems (GNSS) that uses very accurate national atomic clocks on the ground may help self-driving cars in urban environments get where they are going. Researchers from Delft University of Technology (TU Delft), Vrije Universiteit Amsterdam, and VSL have prototyped a hybrid optical–wireless mobile network infrastructure called SuperGPS that can broadcast precisely timed messages using a country’s atomic clocks. The researchers tested the idea in a prototype system on a few streets in that showed accuracy within 10 centimeters (approx. 4 inches).

“We had already been investigating techniques to distribute the national time produced by our atomic clocks to users elsewhere through the telecommunication network,” said Erik Dierikx of VSL, in a press report. “With these techniques we can turn the network into a nationwide distributed atomic clock — with many new applications such as very accurate positioning through mobile networks. With the hybrid optical-wireless system that we have demonstrated now, in principle anyone can have wireless access to the national time produced at VSL. It basically forms an extremely accurate radio clock that is good to one billionth of a second.”

‘TU Delft/Stephan Timmers’

Atomic clocks keep SuperGPS system accurate. Source: TU Delft/Stephan Timmers

Most GNSS constellations broadcast to Earth-based receivers that needs a clear sky view of a satellite, which is more difficult in urban environments. The receivers also are prone to errors owing from multipath propagation and an obstructed view of the sky.

The system could be useful for automated vehicles, quantum communication, and next-generation mobile communication systems, according to the researchers. The research was published in Nature.DOI: 10.1038/s41586-022-05315-7

Traveling phonons transmit and store qubits

Also from TU Delft, physicists from the Gröblacher lab tested and found that using traveling phonons — wave packets from mechanical vibrations — on a silicon quantum chip can function as a network linking different quantum device types and qubits to each other. Phonons promise to be useful in quantum computing because they can couple with photons or electrons, and they are small and move relatively slowly. The researchers Simon Gröblacher and first co-authors Amirparsa Zivari and Niccolò Fiaschi found they could create a traveling entanglement between a phonon and another particle. “Entanglement is the main resource for quantum information and communication,” Zivari told TU Delft’s press office. “We created a traveling entangled state on our chip, which is very useful for connecting two qubits. But we’ve also shown that the phonons travelling through our chip are entangled with photons, light particles. We can use these photons to transfer information over long distances, which means the information is not just stored on our chip, but we could in principle also send it to another city with an optical fibre.” The team was able to manage the phonon’s path in a more controlled manner than previous experiments, which means the phonon can be useful in transmitting and storing qubits. The research findings were published in Science. DOI: 10.1126/sciadv.add281

Future magnetic whirlpool memory saves power

Scientists at the U.S. Department of Energy’s (DOE) Argonne National Laboratory are studying skyrmions — tiny magnetic vortices — to see how they operate in different conditions, including temperature changes.  Skyrmions, which arise from the spin of electrons in certain two-dimensional materials, may be an energy efficient replacement for bar magnets in memory. MIT is also looking at skyrmions for data storage. Using an artificial intelligence program designed for high-power electron microscope that can visualize skyrmions in samples at very low temperatures. The DOE scientists found that in their sample magnetic material, a mixture of iron, germanium and tellurium, that skyrmions have an ordered pattern at minus 60 degrees Fahrenheit and above. Under minus 60, the pattern is disordered, hitting total disorder at minus 270 degrees Fahrenheit. The orderly pattern returns as the temperature goes up above minus 60. The order-disorder transition can be used in the future for memory. “We estimate the skyrmion energy efficiency could be 100 to 1000 times better than current memory in the high performance computers used in research,” said Arthur McCray, Northwestern University graduate student working in Argonne’s Materials Science Division.

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