Much of modern electronics and computer technology is based on one idea: adding chemical impurities, or defects, to semiconductors to alter their ability to conduct electricity. These modified materials are then combined in different ways to produce the devices that form the basis of digital computing, transistors and diodes. Indeed, some quantum information technologies are based on a similar principle: adding specific defects and atoms in materials can produce qubits, the fundamental information storage units of quantum computing.
Gaurav Bahl, a professor of mechanical science and engineering at the University of Illinois at Urbana-Champaign and a member of the Illinois Center for Quantum Information Science and Technology, explores how special nonlinear properties in Engineered materials can achieve similar functionality without needing to intentionally add flaws. As reported by his research group in his paper “Self-Induced Dirac Boundary State and Digitization in a Nonlinear Resonator Chain” published in Physical Review Letters, a metamaterial can alter its functionality on its own depending on the power level of the Starter.
A metamaterial is an artificial system that reproduces the behavior of real materials made of natural atoms. The researchers built one whose behavior is analogous to a special type of semiconductor called Dirac material. It was a chain of magneto-mechanical resonators, where magnetic interactions acted as bonds between atoms in a one-dimensional crystal. When one of these “atoms” was mechanically excited, i.e. caused to move periodically, the excitation spread to the rest of the crystal, just like electrons injected into a semiconductor .
After demonstrating that a completely uniform Dirac metamaterial does not allow mechanical excitations to pass (just as electrons are forbidden to pass through an insulating semiconductor), the researchers introduced a specific set of nonlinearities into the system. This new property added sensitivity to mechanical excitation and could subtly alter the resonance energy of magneto-mechanical atoms. With the right choice of nonlinearity, the researchers observed a sharp transition from insulating behavior to conducting behavior depending on the input force provided.
This intriguing behavior resulted from the spontaneous appearance of a new frontier where the effective mass of the mechanical excitation, an invisible internal property of Dirac materials, underwent a change of sign according to the level of the excitation. The researchers were surprised to find that this boundary was accompanied by a new state that “appeared” at the boundary and allowed the input energy to transmit through the material. This effect was very similar to how a defective atom acts in a semiconductor.
“In photonics and electronics,” Bahl said, “nonlinear properties like this could be engineered to form the basis of new computing systems that don’t rely on the conventional semiconductor approach.”
Every time we add defect states and special atoms, we break the uniformity of the material, which can lead to other unwanted effects. However, materials in which a defect state can be formed on demand through an invisible property, such as the Dirac mass used in this work, have profound implications for quantum information systems where they promise qubits that can be produced dynamically where they are needed. The next challenge is to find or synthesize real materials based on natural atoms capable of reproducing this effect.
The experiments were performed by physics graduate student Gengming Liu in collaboration with postdoc Dr. Jiho Noh and MechSE graduate student Jianing Zhao
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Materials provided by University of Illinois Grainger College of Engineering. Original written by Michael O’Boyle. Note: Content may be edited for style and length.
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Researchers show new way to induce useful defects using invisible material properties News Physics and Quantum Computing
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