Pri Narang and Sergio Carbajo look to advance quantum science for next-gen sensors

For more than a century, scientists have observed that the rules of physics are very different at the smallest scales. Tiny particles’ exact locations can be hard to pin down, and a single particle can seem to be in more than one place, a state called superposition.

At the same time, two particles’ properties can be linked across what seems like improbable distances, a state called entanglement.

Some of today’s most widespread technologies — smartphone touchscreens among them — make use of counterintuitive quantum behaviors, such as superposition and entanglement. And many researchers are pursuing quantum science’s potential to revolutionize computing.

Two members of the California NanoSystems Institute at UCLA are working together to understand the incredibly fast interactions between particles that take place at infinitesimally tiny scales. Professors Prineha “Pri” Narang and Sergio Carbajo aim to harness their findings by developing technology for taking measurements with previously impossible levels of sensitivity.

Their investigations could, for example, measure the air we breathe in ways that better describe the complex climate system and provide information that shapes better decision-making about pollution and other public health concerns.

“Climate is an area that needs new measurement,” said Narang, a professor of physical sciences who holds UCLA’s Howard Reiss Career Development Chair. “It’s an application that excites me because it would showcase the power of quantum technologies with real-world impact in climate science.”

Some quantum measurements are already underway elsewhere. The highest-profile example is gravitational wave detectors such as LIGO, which garnered the 2017 Nobel Prize in physics for its founders. Such observatories characterize distant cosmic events by picking up subatomically sized wobbles in the paths of laser beams.

One way to look at quantum sensing is as the flip side of quantum computing.

Even as quantum computers begin to perform calculations beyond the reach of conventional ones, a major challenge still stunts progress. The basic unit of quantum computing power — the quantum bit, or qubit — must be maintained in a state where it displays counterintuitive behaviors such as entanglement. Doing so requires very specific conditions, because the qubit is extremely sensitive to changes in its environment.

In the quantum sensors that Carbajo and Narang envision, that sensitivity to change becomes the signal used, for instance, to detect certain chemicals in the air. The sensors’ capabilities for measurement would increase if the qubits are entangled. The result could be devices that measure compounds in the air that affect health or the climate system, but are present at concentrations so low that they cannot be measured by current instruments.

“When you measure enough points, you can draw out information that you wouldn’t be able to just by adding up measurements from different systems,” said Carbajo, a UCLA assistant professor of electrical and computer engineering and of physics and astronomy. “The entangled network has a much higher potential capacity for information.”

Narang came to UCLA from Harvard University in July 2022, but she and Carbajo had connected even before her arrival.

“The announcement went out that I was moving here, and one of the first people to write me a warm email was Sergio,” she said. “He has a knack for bringing people together. He’s one of a kind, of course, but it’s helpful that a lot of people on this campus have that impulse to work together with scientific colleagues to solve a problem.”

Thanks in part to CNSI’s interdisciplinary ethos, Narang and Carbajo are engaging colleagues across quantum science and engineering, applied math, atmospheric chemistry, oceanic sciences, geoscience and materials science. (“Basically, three-quarters of the departments in physical sciences and engineering,” Narang said.)

As the two investigators seek to make UCLA a hub for research in this emerging field, they also want to make the field more inclusive.

“Every one of us has a wealth of lived experience, and when we’re more open and inclusive, our ideas will be fresher, our frameworks for understanding richer,” said Carbajo, who is also an equity, diversity and inclusion officer for the department of electrical and computer engineering at the UCLA Samueli School of Engineering. “That means removing barriers to entering this field and asking new questions. If we don’t put that goal at the center of how we perform scientific inquiry, it hurts society as a whole.”

His and Narang’s push for broader participation, focused on inclusion that values differences, also guides the applications they seek to realize. For example, they hope their work leads to technologies that — because they would be more compact and portable, and less expensive than existing tools — respond more directly to the needs of people who are most vulnerable to the effects of the climate crisis and other environmental hazards.

They also plan to train and collaborate with researchers with wider, cross-disciplinary backgrounds, empowering them to exploit the unique advantages that derive from the quantum world’s counterintuitive rules.