Creating New Paradigms for Quantum Technology

When Chris Caron was a middle schooler growing up in West Springfield, MA, he picked up a book on quantum mechanics that changed how he saw the world. Titled The Elegant Universe: Superstrings, Hidden Dimensions, and the Quest for the Ultimate Theory, the pop science book by Brian Greene set Caron on a long-term path of scientific inquiry that today has him playing an essential role in groundbreaking quantum computing research at UMass Amherst.

“This book made me realize that all of the stuff I had been learning in school was only part of the full story, and I wanted to know more,” he recalls.  

Caron peppered his parents with questions. As professional artists who co-own a graphic design business, they were out of their element, so his mom reached out to the then-head of the UMass Amherst Department of Physics for help. She was introduced to Professor Emeritus William Mullin, who kindly entertained Caron’s many questions, answering them in short written chapters. According to Caron, Mullin ultimately incorporated these notes into a book, Quantum Weirdness, published by Oxford University Press, which promises “a fascinating introduction to some of the more bizarre aspects of quantum mechanics.”

“Professor Mullin very significantly altered the course of my life. I owe him a lot,” Caron says.

With this foundation, Caron was hooked. He went on to attend UMass Amherst for his undergraduate education, earning a dual degree in electrical engineering and physics. In fall 2021, he enrolled in a master’s program at UMass in electrical engineering and joined the UMass⁺ Trapped Ions and Photonics Lab under Robert Niffenegger, who had recently come to UMass as an assistant professor of electrical and computer engineering and adjunct in physics. After earning his master’s degree in the spring of 2023, Caron began working toward his PhD in physics at UMass the following fall. 

For Caron, whose academic interests have always spanned electrical engineering and physics, the UMass⁺ Trapped Ions and Photonics Lab provides an ideal combination of both. The lab is focused on creating new trapped ion quantum processor designs, with the researchers' ultimate goal to enable scalable quantum computing. 

From left, Robert Niffenegger, assistant professor of electrical and computer engineering, and Chris Caron, PhD student in physics, in the UMass⁺ Trapped Ions and Photonics Lab.

Caron explained the promise of quantum computers. While classical computers rely on “bits”—binary digits that represent either a zero or one—quantum computers use “qubits” (quantum bits), which allow access to additional operations such as “entanglement” and “superposition.”

"If you have those two additional operations, you can rewrite a lot of very difficult computations in ways that should be faster to compute,” says Caron. “It’s important to understand that the goal is not to replace classical computers. Quantum computers are actually much worse at doing most traditional computations. However, with quantum computers, you can do things like factor a very large number or search through large datasets to find an answer to a question.”

Potential applications, which are famously difficult to do on classical computers, are found in simulation, drug discovery, cryptography, and machine learning, says Caron.

Quantum computing will require many qubits that can retain their information and interact easily with each other. Qubits can be made with superconducting circuits, but the UMass⁺ Trapped Ions and Photonics Lab uses "trapped" ions, positively charged atoms that have had an electron removed. Before using these ions as qubits, they must be trapped, and Caron has worked to fabricate and package these ion trap chips entirely at UMass—rare for a university lab. The chips are about a centimeter square in size and patterned with metal electrodes, which can confine the ions and push them to the center of the chip.

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In contrast to the large, ultra-cold dilution refrigerators used to produce superconducting qubits, the UMass⁺ Trapped Ions and Photonics Lab currently uses a compact, room-temperature vacuum chamber. Inside the chamber, a source of strontium (a soft, silvery metal) is heated up, causing it to emit strontium atoms, which fly toward the chip. A set of lasers then removes one outer electron from each atom, leaving it with a net positive charge and allowing it to become trapped by electric fields created by the chip. More lasers are used to cool the ion and prepare its quantum state. The trapped ion also scatters this laser light, which can then be seen using a sensitive camera to verify the ion is trapped and detect its quantum state after various qubit gate operations.

"Building an ion trap apparatus from scratch, including the fabrication, is not an easy task and one that few other laboratories in the world have achieved,” says Niffenegger. “We were able to do it on our first try, due to Chris’s careful attention to detail fabricating the trapped ion chips.”

“With this process, once we can trap one ion, we can trap five, or 10, or 1,000, or 5,000, just by changing the parameters of the electrical field,” explains Caron. “But to do quantum computing, what you really need is to control every individual ion, which sounds like it would require a full array of lasers aimed at each one.”

The challenge ahead is figuring out a way to scale up the process to control hundreds or thousands of ions at once. “That’s the ‘space race’ that is trapped ion quantum computing right now,” Caron says.

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 “I hope that our research breaks conventions and creates new paradigms for quantum technology—pushing the field toward things that we consider now as impossible, like building a portable quantum computer,” says Niffenegger. 

As of early 2024, the group is nearly a year into routine ion trapping. Soon, they expect to have their first set of results and publications generated from their first working ion trap chip. The system, which Caron helped to create during the course of his master's thesis, now serves as a "testbed" to investigate new ion-trapping techniques. Thus far, the group has succeeded in developing a new chip fabrication process, new techniques for designing circuit boards in ultra-high vacuum chambers, and several novel approaches to the layout and design of the lasers needed for trapping ions. Now, early in his PhD, Caron is working towards refining the design of the subsystems for future applications like general quantum computing, as well as towards using the same system for quantum sensing applications (for example, as the basis for optical clocks, which are poised to become the new standard for the definition of the second).

“It’s really interesting work because it’s so multi-disciplinary, touching on a broad range of subjects,” says Caron. “That’s what drew me to it, and what keeps me here.”

The field of quantum computing is changing so rapidly that Caron can’t predict what it will look like by the time he completes his PhD. Yet through his work, he says, he is developing numerous, varied skills that will be useful wherever he ends up.

Overall, Caron has found UMass to be a supportive setting, full of opportunity.

“At a big university, it can be daunting to find your place, especially in research,” he says. “But because there’s so much going on at UMass, you have a lot of freedom to explore your interests, and—no matter what they are—you'll find a place to pursue them.” 

Photo credit (unless otherwise noted): Derrick Zellmann. This story was originally published in January 2024.