Study Shows Lasers Can Control Magnetic Ripple Interactions

Study Shows Lasers Can Control Magnetic Ripple Interactions

Edoardo Baldini/University of Texas at Austin

Illustration of the crystal structure of the yttrium alloy, with the red line at left representing the laser pulse in and the blue and green lines at right representing the two types of magnons created.

Main points

  • If computers utilized ripples in magnetic fields, known as magnons, to encode and process information, the result would be devices with potential memory speed on the order of billionths of a second.
  • UCLA researchers and partners induced two distinct types of magnons to interact so that output is not directly proportional to input — a critical step toward computing advances.
  • This multi-institution, long-term research collaboration is examining magnons using a seldom used but promising terahertz laser technology.

One view for the future of computing involves using ripples in magnetic fields — known as magnons — as a basic mechanism. In this context, magnons would be equivalent to electricity as the foundation for electronics.

In traditional digital technologies, such magnonic systems are anticipated to be much faster than today’s technologies, from laptops and smartphones to telecommunications. In quantum computing, the benefits of magnonics could encompass not only quicker speeds but also more stable devices.

A recent study in the journal Nature Physics details an early-stage discovery along the path to developing magnonic computers. The researchers induced two distinct types of ripples in the magnetic field of a thin plate of alloy, measured the results and demonstrated that the magnons interacted in a nonlinear manner. “Nonlinear” refers to output that is not directly proportional to input — a necessity for any type of computing application.

To date, most research in this area has focused on one type of magnon at a time, under relatively stable conditions described as equilibrium. Manipulating the magnons, as done in these studies, pushes the system out of equilibrium.

This is one of numerous investigations underway through a multiyear collaboration between theorists and experimentalists from various fields of science and engineering, including a second study that recently appeared in Nature Physics. The project, supported by government and private grantors, brings together researchers from UCLA, MIT, the University of Texas at Austin and the University of Tokyo in Japan.

“With our colleagues, we’ve initiated what I would call a campaign to stimulate progress in nonequilibrium physics,” said Prineha Narang, a co-author of the study and professor of physical sciences at UCLA College. “What we’ve accomplished here fundamentally advances the understanding of nonequilibrium and nonlinear phenomena. And it could be a step toward computer memory using ultrafast phenomena that occur on the order of billionths of a second.”

A key technology behind these findings is an advanced technique for adding energy to and evaluating samples using lasers with frequencies in the terahertz range, which sits between the wavelengths of microwave and infrared radiation. Adopted from chemistry and medical imaging, the method is applied only rarely to study magnetic fields.

According to Narang, who is a member of the California NanoSystems Institute at UCLA, the use of terahertz lasers suggests potential synergy with a technology growing in maturity.

“Terahertz technology itself has reached the point where we can discuss a second technology that relies on it,” she said. “It makes sense to perform this type of nonlinear control in a band where we have lasers and detectors that can be put on a chip. Now is the time to really push forward because we have both the technology and an interesting theoretical framework for looking at interactions among magnons.”

The researchers applied laser pulses to a 2-millimeter-thick plate made from a carefully chosen alloy containing yttrium, a metal found in LEDs and radar technology. In some experiments, a second terahertz laser was used in a coordinated way that paradoxically added energy but helped stabilize samples.

A magnetic field was applied to the yttrium in a specific manner that allowed for only two types of magnon. The investigators were able to drive either type of magnon individually or both at the same time by rotating the sample to certain angles relative to the lasers. They were able to measure the interactions between the two types and found that they could cause nonlinear responses.

“Clearly demonstrating this nonlinear interaction would be important for any type of application based on signal processing,” said co-author Jonathan Curtis, a UCLA postdoctoral researcher in the NarangLab. “Mixing signals like this could allow us to convert between different magnetic inputs and outputs, which is what you need for a device that relies on manipulating information magnetically.”

Narang said that trainees are essential to the current study, as well as the larger project.

“This is a really hard, multiyear endeavor with a lot of pieces,” she said. “What’s the right system and how do we go about working with it? How do we think about making predictions? How do we limit the system so it’s behaving as we want it to? We wouldn’t be able to do this without talented students and postdocs.”

The study includes MIT chemistry professor Keith Nelson and UT Austin physics professor Edoardo Baldini, along with the UCLA team led by Narang, which was supported by the Quantum Science Center, a Department of Energy National Quantum Information Science Research Center headquartered at Oak Ridge National Laboratory. The study was primarily supported by the Department of Energy as well as the Alexander von Humboldt Foundation, the Gordon and Betty Moore Foundation, the John Simon Guggenheim Memorial Foundation and the Japan Society for the Promotion of Science — all of which provide ongoing support for the collaboration.

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