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Photo of Irena Knezevic
5/10/2017

Professorship aids Knezevic’s quantum mechanics research

Written By: Pat DeFlorin

Smartphones, smartwatches, laptops, Fitbits—all consumer electronics rely on the physics of things you cannot see.

Irena Knezevic, a professor of electrical and computer engineering at the University of Wisconsin-Madison, seeks to better understand this nanoscale physics to improve our lives.

She recently received the Patricia and Michael Splinter Professorship in Electrical and Computer Engineering to support her in that endeavor.

The Splinter professorship, created by electrical and computer engineering alumnus Michael Splinter (BS ’72, MS ’74) and his wife Patricia, supports Knezevic as she studies quantum mechanics, the physics of things at atomic and subatomic scales. Specifically, she works to understand how charge, light and heat interact in nanoscale systems. To do so, she makes mathematical models to explain the physics in these systems and writes computer code to solve the models. “Quantum mechanics is the physics of things you can’t see,” says Knezevic. “And the best way to deal with the things you can’t see is with math.”

Knezevic focuses on the behavior of electrons. What makes small objects like electrons differ from large objects is that they behave more like waves than particles. Knezevic works to understand what happens when you confine the dynamic wavelike behavior of electrons to nanoscale dimensions.

One area of her research focuses on quantum cascade lasers, which can emit more light energy than standard lasers. Knezevic simulates the physics of these devices and shares her findings with collaborators who apply her work to build improved quantum cascade lasers. The lasers go on to be used for imaging, telecommunications, trace gas analysis—anything with a sensor that has a light emitter.

Worldwide, few researchers are doing similar quantum cascade laser modelling. Although other groups are researching the lasers, what sets Knezevic’s work apart is that her models are multiscale and multiphysics models. Multiscale meaning she studies the lasers from the atomic level of photon and electron behavior all the way up to the micron level of the whole laser; multiphysics meaning she investigates the interplay between charge, light and heat within the entire system. Since other groups studying quantum cascade lasers often look primarily at electron transport, Knezevic’s holistic inquiry is state-of-the-art.

In addition to quantum cascade lasers, Knezevic studies nanomaterials such as graphene, a single-layer lattice of carbon atoms. Due to its exceptional strength and conductivity, graphene has myriad potential applications from solar cells to biosensors. “One of the coolest things about graphene is understanding how it behaves when you put it on different materials,” says Knezevic.

When you take pieces of graphene and roll them up like cannoli, you create carbon nanotubes.

Knezevic studies how carbon nanotubes capture light energy by temporarily binding it into ephemeral particles known as excitons. She explores the behavior of excitons in disordered nanotube systems to better understand how light energy moves from nanotube to nanotube on the way from where it was absorbed to where it is being collected. Currently, carbon nanotube films are an inexpensive way to harvest solar energy. They are also inefficient. Knezevic hopes her research will lead to more efficient solar cells that can be implemented globally.

The Splinter professorship supports Knezevic’s current research, and allows her to venture into new research areas, like nanoscale antennas. Nanoscale antennas are like standand radio antennas, but much smaller. This makes them behave unexpectedly. “When you make antennas small, there is physics that arises that wasn’t there when the antenna was bigger,” says Knezevic.

By marrying her knowledge of light emission at the nano scale with her knowledge of quantum transport, Knezevic aims to better understand the fundamental workings of nanoscale antennas. This research will help to shape the future of telecommunications and sensing.

The Splinter professorship also funds a graduate research assistant with whom Knezevic will share her passion for the beauty of quantum mechanics. And, at the end of the day, she aims to share that passion not only with her students, but with us all. “Beautiful math and physics underlie all of engineering,” says Knezevic.


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