Acoustic resonances in devices such as smartphones and Wi-Fi systems degrade over time, but there is no easy way to monitor this degradation. Researchers from Harvard SEAS and Purdue University have now developed a method to use atomic vacancies in silicon carbide to measure the stability of these resonators and even manipulate quantum states, potentially benefiting future developments in accelerometers, gyroscopes, clocks and quantum networks.
Using sound waves to control atomic vacancies could enhance communications technology and provide new control mechanisms for quantum computing.
Acoustic resonance is everywhere. In fact, there's a good chance you're holding one in your hands right now. Most smartphones today use bulk acoustic resonators as RF filters to filter out noise that can degrade signal quality. These filters are also used in most Wi-Fi and GPS systems.
Acoustic resonators are more stable than electronic resonators but can also degrade over time. There is currently no easy way to proactively monitor and analyze material quality degradation in these widely used devices.
Now, researchers at Harvard's John Paulson School of Engineering and Applied Sciences (SEAS), in collaboration with researchers at Purdue University's OxideMEMS Laboratory, have developed a system that uses atomic vacancies in silicon carbide to measure the stability and quality of acoustic resonances. What's more, these vacancies can also be used for sound-controlled quantum information processing, providing a new way to manipulate quantum states embedded in this commonly used material.
"Silicon carbide, which hosts both quantum reporters and acoustic resonance probes, is an off-the-shelf commercial semiconductor that can be used at room temperature," said Evelyn Hu, the paper's senior author and Tal-Coyne Professor in the Departments of Applied Physics and Electrical Engineering and the Robin Li and Weihua Ma Professor in the College of Arts and Sciences. "As an acoustic resonance probe, this technology in silicon carbide could be used to monitor the performance of accelerometers, gyroscopes and clocks over their lifetime, and in quantum scenarios could potentially be used in hybrid quantum memories and quantum networks."
The research was published in Nature Electronics.
Silicon carbide is a commonly used material in microelectromechanical systems (MEMS), including bulk acoustic resonators. "Wafer-scale manufacturable silicon carbide resonators in particular are known to have best-in-class figure-of-merit performance," said co-author Sunil Bhave, professor in the Elmore Family School of Electrical and Computer Engineering at Purdue University. "However, crystal growth defects, such as dislocations and grain boundaries, and resonator manufacturing defects, such as roughness, system stresses, and microscale pits, can create areas of stress concentration within MEMS resonators."
Today, the only way to see inside an acoustic resonator without destroying it is to use ultra-powerful and very expensive X-rays, such as Argonne National Laboratory's broad-spectrum X-ray beam.
"These types of expensive and inaccessible machines cannot be measured or characterized in a foundry or where these devices are actually manufactured or deployed," said Jonathan Dietz, a SEAS graduate student and co-first author of the paper. "Our motivation was to try to develop a method that would allow us to monitor the acoustic energy inside a bulk acoustic resonator so that you could feed those results back into the design and manufacturing process."
Silicon carbide often has natural defects in which an atom is removed from the crystal lattice, creating a spatially localized electronic state whose spin can interact with acoustic waves through material strain, such as that produced by acoustic resonators.
When sound waves pass through the material, they create mechanical strains in the crystal lattice, causing the spins of the defects to flip. Changes in the spin state can be observed by shining a laser on the material to see how many defects "open" or "close" after being perturbed.
"How dark or bright the light is indicates how strong the acoustic energy is in the local environment where the defect is located," said Aaron Day, a graduate student at SEAS and co-author of the paper. "Because these defects are only the size of a single atom, the information they provide is very localized, so you can actually map the acoustic waves inside the device in this non-destructive way."
The map can indicate where and how the system may be degrading or not operating optimally. These defects in silicon carbide can also become qubits in quantum systems. Today, many quantum technologies are based on spin coherence: how long a spin remains in a specific state. This coherence is usually controlled by magnetic fields.
But Hu and her team used their technique to show that they could control the spins by mechanically deforming the material with sound waves, achieving a similar quality of control to other methods using alternating magnetic fields.
"Taking advantage of a material's natural mechanical property -- strain -- expands the scope of our material control," Hu said. "When we deform the material, we found that we can also control the coherence of the spins, and we can obtain this information simply by sending sound waves through the material. This gives us an important new tool for intrinsic material properties that we can use to control the quantum states embedded in the material."