A Close Look at Physical Sciences

by Alan S. Brown

Self-assembling nanoarchitectures and light for quantum networks

The Author

Alan S. Brown

The Researchers

Julia Greer
Alex Zettl
Andrei Faraon
Kerry Vahala
Cees Dekker

​​Given all the news about the coronavirus pandemic, it might be nice to escape for a few minutes into the nanoscale workings of the world. Whether it is self-assembling complex nanoarchitectures in hours rather than months or teasing light for a quantum network from a rare earth element that does not interact well with light, this month’s nanoscience news roundup takes a close look at the physical sciences (and also, a surprising way our cells pack DNA into chromosomes).

Self-assembly, on the double

Julia Greer, director of the Kavli Nanoscience Institute at Caltech, is well known for growing exotic structures the size of a DNA molecule. Some look like the trusswork of the Eiffel Tower or an old-fashioned railroad bridge, but at the nanoscale, they have unusual properties. She can, for example, grow a small cube of trusses made of ceramic, an easily fractured brittle material, pops back into shape after compressing it. The trouble is that it takes an enormous amount of time to makes these wonders with laser light, truss by truss. Now, working with a team at ETH Zurich, Greer’s team has developed a process that self-assembles curved shells into cubic centimeter amounts of structures in hours instead of months. Some samples show strength-to-density ratios comparable to some forms steels, while others spring back after repeated compression. Potential applications range from ultrasensitive tactile sensors to electrodes for advanced batteries.

Rocking to the graphene sound

When most people hear the word “graphene”—if they even know what it is—they think of an exotic material. Yet this material could be showing up in high-end headphones and microphones within a year or two. The sound quality is so clear, listeners can pick out an individual instrument’s tones in a symphony orchestra, said Ramesh Ramchandani, CEO of GraphAudio, who demonstrated the headphones at the Consumer Electronics Show in January. The material itself was developed by Alex Zettl, a member of the Kavli Energy NanoScience Institute at UC Berkeley. To form a speaker, a film of graphene only a few atoms thick sits between two silicon-based electrodes. The graphene translates electrical pulses from the electrode into sound with minimal distortion throughout the entire sonic range. It is so energy-efficient—99 percent vs 10 percent for ordinary speakers—that batteries will last longer without a charge. Other potential uses for the technology: ultrathin car speakers, echolocation sensors to avoid vehicle collisions, submarine communications, and medical ultrasound sensors.

Quantum forevers

Thirty thousandths of a second doesn’t sound like a lot of time, but when it comes to remembering quantum information, it is an eon. This is how long a new device developed by Andrei Faraon, a member of the Kavli Nanoscience Institute at Caltech, can store quantum data, and it could prove critical for quantum networks. One type of network works by storing information in a quantum property of an atom, like its spin. To transmit this data, the network entangles the spin with a particle of light (photon) that it sends over optical cable to another quantum computer. Any change in the first qubit then shows up in the entangled photon. To do this, you need an atom you can control and that doesn’t lose its quantum properties when you measure it. Rare earth elements usually fill the bill, but they interact poorly with light. Faraon’s contribution is a cavity that captures and retains a single rare earth ion, ytterbium, and captures every photon it emits until it has enough of them to send over a cable—and it stays stable long enough to actually do some computing once the entangled photon gets where it is going.

New spin on gyroscopes

Lots of video games use gyroscopes in controllers or smartphones to pinpoint how you twist and turn. These gyros consist of tiny mechanical features etched into inexpensive chips. They work great for games, but not for airplanes or long-distance drones. This is because they are not sensitive enough to changes in the earth’s rotation. To pick that up, engineers opt for larger optical gyroscopes, which send two laser beams down a circular path in opposite directions. Ordinarily, they would meet at the same point every time around. But as the earth rotates, it changes the amount of time the beams need to reach that point by a tiny amount. This information improves precision. Now, Kerry Vahala of the Kavli Nanoscience Institute at Caltech, has found a way to shrink this optical gyro down to a circular silica disk—and generate laser light from high-frequency vibrations within the disk. This opens the door for a new generation of ultra-precise gyros for all aerospace and other applications.

Zigzagging DNA into chromosomal suitcases

A cell’s DNA normally looks like floating nanoscale strands of cooked spaghetti. When cells divide, a protein called condensin—great name, right? —plays a role in spooling this tangle into packed chromosomes. Two years ago, a team led by Cees Dekker of the Kavli Institute of Nanoscience at Delft University of Technology and researchers from EMBL Heidelberg showed how condensin looped that DNA spaghetti to bundle it together. Now, they have found that when more than one condensin protein is involved, they pack that chromosomal suitcase in a completely different way. Together, they create a zigzag structure the researchers call a Z loop. And, like much else in nature, how it gets there is entirely unexpected. First, one protein starts making a loop, then another starts making a loop within that loop. When the two meet, the second protein vaults over the first and just keeps going. You can read more about the details here.

Written by Alan S. Brown

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