Huanqian Loh: Exploring Quantum Systems with Neutral Atoms

Huanqian Loh joined the faculty of the Department of Electrical and Computer Engineering at Duke University as an assistant professor on July 1, 2024. With broad experience in quantum computing technologies and a focus on neutral atom systems, Loh adds a new dimension to the growing capabilities of the Duke Quantum Center (DQC).

Launched in 2020, the DQC conducts research on all aspects of quantum computing from hardware to theoretical control approaches while building physical systems with world-leading capabilities and training tomorrow’s quantum workforce. While its original primary work focused on systems that use trapped ions as their “qubit” fundamental building blocks, the center continues to add expertise in a variety of approaches that have much in common and could prove complementary to each other.

Loh’s area of expertise is in quantum systems built from neutral atoms that are controlled by optical tweezers. Trapped ions rely on an atom’s electrical charge to keep it in place, but that approach does not work on neutral atoms. Instead, this approach uses an incredibly focused laser to create a tight trap that can keep tiny objects at its focal point. The idea has so many potential applications that it won its inventors the Nobel Prize in physics in 2018.

“One major difference between neutral atom systems and other approaches is that the optical tweezers can move the atoms around to form flexible geometries,” said Loh, who joins Duke from the Centre for Quantum Technologies at the National University of Singapore, where she has been a faculty member for seven years. “This ability provides these quantum systems with unique opportunities.”

For example, one of the primary approaches to using quantum bits to form a computer is a phenomenon called entanglement, which forces two quantum bits, or “qubits,” to become intimately linked no matter how far apart they later become. With the ability to reconfigure atoms in real-time, researchers can entangle many qubits to perform powerful calculations.

Forming specific patterns with the atoms can also help researchers create quantum simulators to study complex phenomena in nature, like transport in advanced materials. For example, neutral atom qubits can be arranged in hexagons to emulate graphene. In fact, since the neutral atoms can be pristinely controlled in a versatile manner, properties of new synthetic materials that have not yet been realized in nature can also be explored. Besides materials, there are problems in other fields like nuclear physics that Loh is looking to solve with her neutral-atom quantum computers.

“In industry, lots of startup companies are forming around the ability of neutral atom arrays to efficiently solve optimization problems by arranging the atoms in a particular graph. This is another exciting direction because it has direct applications to many industries such as shipping and telecommunications,” Loh said.

Loh began her interest in quantum systems as an undergraduate student at the Massachusetts Institute of Technology. Attracted to physics-based questions in a wide variety of fields, she eventually found a home in quantum physics because of the opportunity to build systems from scratch. By having to engineer all her experiments, it gave her a deeper understanding of how they worked and what was going on inside of them.

Loh then earned her PhD in physics from one of the quantum field’s long-standing innovative institutions, the University of Colorado – Boulder. Besides looking for oddities in the behavior of electrons to probe physics beyond the Standard Model with benchtop experiments, she also met her future husband, Travis Nicholson, who has recently started a joint appointment in physics and electrical and computer engineering at Duke.

“We’re both very excited to be coming to Duke because of the growth and expertise of the DQC,” Loh said. “We know it’s going to continue growing into something very big, and it’s exciting to get to be a part of that.”

Even though Loh may use a different approach to building quantum computers, many of the challenges she’s facing are the same as everyone in the field. For any type of computer to be reliable, it must have a way of detecting and correcting errors in its processing. And most systems being pursued at Duke also require strong expertise in photonics to precisely control the lasers that link the whole system together.

With these hurdles top-of-mind, Loh says she’s excited to collaborate with a handful of Duke researchers who are top experts in these fields, such as Ken Brown, a leader on error correction, Chris Monroe, a pioneer of ion-trap-based quantum computers, and Jungsang Kim and Crystal Noel, who are specialists in using photonics to engineer robust quantum setups.

She is also looking forward to working with the fantastic students that Duke attracts. This fall, she’ll be teaching an undergraduate course in optics and modern physics. And later next spring, she’s planning on teaching a new graduate course in quantum simulation.