Quantum sensors built “from the ground up”

What does creating custom-sewn, Edwardian-era-inspired clothes by hand have in common with developing a new class of quantum units or “qubits” controlled by light? 

“To me, both are forms of engineering,” says Chloe Washabaugh.

In her evenings, Washabaugh enjoys making early-1900s-style clothes, a process she describes as drafting and configuring 2D pieces of fabric into patterns that fit the 3D shape of the body. Her day job, however, is advancing a new platform of quantum technology that could aid in environmental sensing as a second-year PhD student in David Awschalom’s group at the University of Chicago Pritzker School of Molecular Engineering. 

The quantum units aka qubits that she’s characterizing are altogether different from another more-established class of qubits being developed by others in Awschalom’s group. The other qubits are made by adding atom-sized defects to superconducting materials, a “top-down” approach. Instead, Washabaugh’s qubits are built from the ground up, relying on chemistry to assemble atoms in ways that achieve specific properties.

“This is an exciting and up-and-coming approach because you can tightly control the qubit’s properties and how the qubit interacts with its environment – perhaps to detect something in the environment,” she says. 

The qubits are also scalable, Washabaugh says, meaning more than one qubit can be combined to create more complex structures. “With the help of chemistry collaborators, we can control single atoms of oxygen, nitrogen, or hydrogen, for example, and place them in branch-like shapes extending outward from a single atom of a transition metal like chromium.”

These optically addressable molecular qubits, as they are called, can be designed to be either extremely sensitive or insensitive to perturbations in the environment like electric fields. To test ensembles of these molecular qubits in the lab, Washabaugh shoots a laser pulse at them and then measures the number of photons they emit, which reveals information about how the qubits are interacting – or not interacting – with the environment around them.

The lab itself is bunker-like by design. The concrete-lined facility is underground, rather than aboveground or on upper floors, because higher levels of buildings experience more vibrations and sway, which can be very problematic when engineering delicate structures on the scale of atoms. The basement location also cuts down on the number of stray magnetic fields that can collide with the lab, where they would interfere with experiments. Among the quantum community, Washabaugh says with a laugh, there is an appreciation for the havoc that nearby metro lines, flushing toilets, and cell phone signals can wreak on their highly sensitive work.

Washabaugh has always loved math and science, and knew as a high schooler she wanted to pursue a career in engineering. She was drawn into the field of quantum by an online video she stumbled across the summer before starting her freshman year at Cornell University. “I watched this YouTube video by WIRED explaining quantum information at five different levels, ranging from expert to elementary schooler. I had this epiphany – I could do quantum engineering,” she says.

PME, prominent within the Chicago Quantum Exchange and known globally as a leader in quantum technologies, quickly attracted Washabaugh’s interest as the ideal destination to earn a PhD. 

“Everyone in the lab is fairly independent in terms of the work they are pursuing,” she says. “It’s very fulfilling to have such a high level of trust placed in me by my advisor and the senior members of the lab. Despite my independence when it comes to my research, together we share dedication to raising awareness about quantum science with the public.”

Outside the lab, Washabaugh is passionate about sharing her love of quantum science with the broader community and world. Alongside peers, she volunteers at UChicago’s South Side Science Festival and Physics with a Bang! event, where “talking about science with children feeds my soul,” she says. 

She’s also involved in PME’s STAGE (Scientists, Technologists and Artists Generating Exploration) Lab, where faculty and student researchers are coming up with creative and artistic ways to communicate science, such as developing casino games that convey key principles of quantum science. On the global scale, Washabaugh traveled to Japan this summer, meeting with quantum peers at the University of Tokyo and Tohoku University to explore opportunities to collaborate on research. 

“PME is a great place to do your PhD, specifically for quantum,” she says. “The PME community has been developing deep relationships locally and internationally within the quantum space.” New arrivals to PME and UChicago may recognize Washabaugh’s warm smile, as she also volunteers for student welcome and orientation weekends, during which she enjoys helping people connect with their new environs. “I have really loved bringing people together at PME.”