Inside Advanced Scale Challenges|Friday, December 14, 2018
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New Device Spots Quantum Particle ‘Fingerprint’ 

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Majorana particles have been observed by university researchers employing a device consisting of layers of magnetic insulators on a superconducting material. The advance opens the door to controlling the elusive particles as part of an alternative “topological” approach to quantum computing being pursued by Microsoft and others.

Majorana particle hunters at the University of California at Los Angeles observed particles using an electronic device that replaced semiconductor nanowires and other previous approaches with stacked layers of magnetic topological insulator. The material was placed on top of a superconductor.

Earlier devices yielded ambiguous results in the search for Majorana particles since they produced “inconclusive signals that could also be attributed to other effects,” said Joe Qiu of the Army Research Office. (The UCLA research is being funded by the U.S. Army Research Laboratory.)

By contrast, the UCLA experiment “demonstrated the clearest and most unambiguous evidence of the [Majorana] particles as predicted by the theory so far,” added Qui, who manages the Army office’s Solid-Sate Electronics Program.

The device demonstrated the ability to steer Majorana particles through transport channels (see drawing). The researchers placed a thin film of topological insulator on top of a superconductor used to eliminate electron resistance. The configuration allowed the researchers to manipulate particles in specific patterns. After applying a tiny magnetic field over their device, they detected the “distinct quantized signal” of Majorana particles in the electrical signals between the materials. The signal represents the “fingerprint” of Majorana particles, the researchers assert.

The device is made up of a superconductor (blue bar) and a magnetic topological insulator (gray strip). The Majorana particles result in transport channels (shown in red, pink, blue and yellow) in the electronic device. (Source: UCLA)

Other investigators continue to pursue the nanowire approach, yielding similar tantalizing evidence about the existence of the particles. These and other approaches raise the possibility of controlling Majorana fermions, that is, a theoretical particle that is its own “antiparticle,” for topological quantum computing.

Microsoft (NASDAQ: MSFT) and a band of Majorana hunters are pursuing the topological approach as an alternative to quantum computing approaches being pursued by Google (NASDAQ: GOOGL), IBM (NYSE: IBM) and startups like D-Wave Systems. Among the claimed advantages of the Majorana approach are greater stability and reduced error correction.

Researchers notes that other properties of the mysterious particle make it a prime candidate for quantum computing, including a neutral charge that makes it more resistant to external interference. That attribute means the particle could help sustain quantum entanglement, an ephemeral property of quantum physics in which entangled particles remain connected so that the actions of one affect the other, even when separated.

That property would allow separate particles to concurrently encode information, opening up the prospect of a proverbial quantum leap in computing power.

“The Majorana particles show up and behave like halves of an electron, although they aren't pieces of electrons," explained Qing Lin He, a UCLA postdoctoral scholar and co-lead author of a paper on the experiment published last July in the journal Science. "We observed quantum behavior, and the signal we saw clearly showed the existence of these particles."

The particles travelled along the edges of the topological insulator in a “braid-like” pattern, the investigators added. Future research will focus on using Majorana particles in quantum braiding, which would knit them together to allow quantum-level data storage and processing.

“Information encoded in a topological quantum computer cannot be easily corrupted," added Lei Pan, a UCLA doctoral candidate and co-author of the Sciencepaper. "What's exciting about using Majorana particles to build quantum computers is that the system would be fault-tolerant."

About the author: George Leopold

George Leopold has written about science and technology for more than 30 years, focusing on electronics and aerospace technology. He previously served as executive editor of Electronic Engineering Times. Leopold is the author of "Calculated Risk: The Supersonic Life and Times of Gus Grissom" (Purdue University Press, 2016).

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