Building materials for a quantum future

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Newswise — Katie Sautter is an architect of exquisite, invisible structures. Built one atomic layer at a time, his team’s atomic engineering samples are the starting points for new materials that could one day enable a quantum network.

A postdoctoral researcher at the US Department of Energy’s (DOE) Argonne National Laboratory, Sautter studies quantum materials as part of Q-NEXTa DOE National Quantum Information Science Research Center established in 2020. Materials from his team’s research will be used in quantum communication devices.

“Materials science is great. We take what people have theorized and process it, pass it on to them and reprocess it until we have a nice shiny thing. This is the foundation on which everything else is built. —Katie Sautter

“Quantum devices have a huge range of potential applications in cybersecurity, computing, data communications and lasers – quantum engineering can take all of this in a direction that cannot be taken with traditional methods” said Sautter, who works with Q-NEXT. within the Nanosciences and Technologies pole of Argonne.

Sautter’s path to quantum engineering began at Pennsylvania State University, where she studied materials science and engineering under the guidance of Jeffrey Brownson, an engineering professor there. When the two first met, Sautter was part of a group of high school students visiting the university. Brownson led the group, and Sautter’s insightful questions caught his attention. After discussing her interests, Brownson gave her some career advice, and she enrolled at Penn State the following year, attracted by the quality of its materials science and engineering program, even though she didn’t did not choose a specialty immediately.

“It took me a while to find my way,” she says. “Then I did an internship at the National Renewable Energy Lab, working with the high-efficiency solar cell team, and I loved it. That’s what prompted me to do my Ph.D. The National Renewable Energy Laboratory is a DOE National Laboratory in Colorado.

Sautter earned his Ph.D. in Materials Science and Engineering in May 2021 from Boise State University, where she became an expert in a special process of growing materials: individual layers of atoms are meticulously stacked on top of each other at the using an instrument called a molecular beam epitaxy (MBE) machine. She used the university’s MBE to create quantum dots, chunks of matter only thousands of atoms wide. Five thousand stitches could fit the width of an average human hair.

Now a member of Q-NEXT, Sautter will help create materials for quantum memories that can be built on silicon chips, working under scientist Argonne, a professor at the University of Chicago and chief technology officer of Q- NEXT, Supratik Guha. His work will contribute to devices that contain quantum memories, analogous to the memory in your desktop computer. If successful, these memories will be used in devices known as quantum repeaters.

Quantum repeaters allow the transmission of quantum information over longer fiber optic distances. As the signal travels along the fiber, it weakens. The quantum repeater repeatedly “stitches” the signal so that the information can be transmitted over the entire length of the fiber. Without them, the signal could die out before reaching its destination. Although quantum repeaters are still in the design stage, they hold great promise for quantum communication.

Researchers are also working to develop quantum memory devices that operate in the telecommunications frequency band, making them compatible with today’s fiber optic networks.

These next-gen devices will need to be built from next-gen materials.

“We’re creating whole new hardware structures that nobody’s ever done before, inventing something new that can be developed for these quantum devices,” Sautter said.

And to do so, she’ll use a purpose-built MBE system in Guha’s lab, a steampunk-yet-sci-fi tool that would fill a large bedroom.

“It feels like something out of Star Trek, like we have a warp drive inside our lab,” she said.

In MBE, different chemical elements are placed in separate compartments of the machine and heated. Like steam from a cup of tea, vapors rise from sources. Shutters allow puffs of molecular vapor to pass out of the compartments and into a central chamber at precise intervals.

The first burst of vapor to enter the chamber lands on a foundation, a wafer, creating the sample’s thin first stage. The next layer is quickly deposited on the first. Thus, the process continues, the atomic layers piling up at high speed. In one to three hours, the MBE builds up enough material for a compact, high-performance device.

The result is a finely crafted molecular tower, an exquisite nanoscopic cake.

One of the advantages of MBE over comparable material construction processes is that it allows extreme control of growth parameters: wafer temperature, lamination rate, and deposition amounts can all be tuned to a T. By turning these knobs, the operator can ensure that, for example, every third layer is exactly 2 nanometers thick.

“That kind of precision with extreme cuts between layers – you could try doing it with something else, but that would be more difficult. MBE makes that process easier,” Sautter said. “The precision is immense.”

MBE also results in exceptionally pure materials. Other processes use certain chemicals to jump-start the production of the desired end product. And while the initial compounds aren’t meant to be part of the final mix, sometimes they end up there anyway. MBE dispenses with these preparatory compounds for the most part, avoiding sample contamination.

Sautter appreciates the concrete nature of molecular beam epitaxy.

“It’s kind of an intense tool, and it can take years to learn,” Sautter said. “If you can solve a difficult problem, like I did at Boise State, whose machine dates back to 1992, you can probably solve a problem with a newer, more refined or more automatic machine. I have been told that the MBE is one of the hardest tools to learn in science because it has so many components.

Sautter and his team in the Guha lab will focus on building oxide heterostructures – materials with layers made up of two or more oxygenates. Their particular structural arrangements and the way they interact with their environment make them ideal for quantum memory processing.

“Materials science is great. We take what people have theorized and process it, pass it on to them, and rework it until we have a nice shiny thing. It’s the foundation on which everything else is built,” Sautter said. “It’s a pretty satisfying science.”

Now she’s using that science to advance another.

“I am excited to do MBE in something similar but different to my PhD. and on a fancy new machine,” she said. “Quantum information science is going to change the planet. It helps everyone.

Q-NEXT is supported by the US Department of Energy’s Office of Science.

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