Insider’s memory
- A Penn-led team of scientists has developed a quantum sensing method that detects signals from individual atoms, providing unprecedented precision in molecular analysis.
- The technique isolates single nuclei to reveal minute differences in molecular structures, enabling advances in areas such as drug development and protein research.
- The discovery was made using nitrogen vacancy centers in diamonds and combines decades-old theory with modern technology, opening new frontiers in quantum physics and spectroscopy.
- Image: An artistic representation of the tiny nucleic differences detectable using the form of quadrupolar nuclear resonance described in the new paper. (Mathieu Ouellet)
PRESS RELEASE — Since the 1950s, scientists have used radio waves to discover the molecular “fingerprints” of unknown materials, contributing to tasks as varied as analyzing the human body with MRI machines and detecting explosives at airports.
However, these methods rely on signals averaged over billions of atoms, making it impossible to detect tiny variations between individual molecules. Such limitations hamper applications in areas such as protein research, where small differences in shape-control functionality can determine the difference between health and disease.
Subatomic information
Now, engineers at the University of Pennsylvania School of Engineering and Applied Sciences (Penn Engineering) have used quantum sensors to achieve a revolutionary variation of nuclear quadrupole resonance (NQR) spectroscopy, a technique traditionally used to detect drugs and explosives or analyze pharmaceutical products.
Described in Nano letters, the new method is so precise that it can detect NQR signals from individual atoms – a feat once thought unattainable. This unprecedented sensitivity opens the door to breakthroughs in areas such as drug development, where understanding molecular interactions at the atomic level is essential.
“This technique allows us to isolate individual nuclei and reveal minute differences in what were thought to be identical molecules,” explains Lee Bassettassociate professor of electrical and systems engineering (ESE), director of Penn’s Quantum Engineering Laboratory (QEL) and lead author of the article. “By focusing on a single nucleus, we can uncover details of molecular structure and dynamics that were previously hidden. This ability allows us to study the building blocks of the natural world on a whole new scale.
An unexpected discovery
The discovery stemmed from an unexpected observation during routine experiments. Alex Breitweiserrecent graduate with a doctorate in physics from Penn’s School of Arts & Sciences and co-first author of the paper, who is now a researcher at IBM, was working with nitrogen vacancy (NV) centers in diamonds – atomic-scale defects often used in quantum sensing – when he noticed unusual trends in the data.
The periodic signals looked like an experimental artifact, but persisted after extensive troubleshooting. Returning to textbooks from the 1950s and 1960s on nuclear magnetic resonance, Breitweiser identified a physical mechanism that explained what they were seeing, but which had previously been dismissed as experimentally insignificant.
Advances in technology have allowed the team to detect and measure effects that were once beyond the reach of scientific instruments. “We realized we weren’t just seeing an anomaly,” Brietweiser says. “We were entering a new regime of physics that we can access through this technology.”
Unprecedented precision
Understanding of this effect has been deepened through collaboration with researchers from Delft University of Technology in the Netherlands, where Breitweiser had spent time conducting research on related topics as part of an international fellowship. By combining their expertise in experimental physics, quantum sensing and theoretical modeling, the team created a method capable of capturing single atomic signals with extraordinary precision.
“It’s a bit like isolating a single row in a huge spreadsheet,” says Matthew Ouelletrecent PhD graduate in ESE and other co-first author of the paper. “Traditional NQR produces something like an average: you have an idea of the data as a whole, but you know nothing about the individual data points. With this method, it is as if we have discovered all the data behind the average, isolating the signal from a core and revealing its unique properties.
Deciphering the signals
Determining the theoretical underpinnings of this unexpected experimental result required considerable effort. Ouellet had to carefully test various hypotheses, run simulations and perform calculations to match the data with potential causes. “It’s a bit like diagnosing a patient based on their symptoms,” he explains. “The data indicates something unusual, but there are often several possible explanations. It took some time to arrive at the correct diagnosis.
Looking ahead, the researchers see vast potential in their method to address pressing scientific challenges. By characterizing previously hidden phenomena, the new method could help scientists better understand the molecular mechanisms that shape our world.
This study was conducted at the School of Engineering and Applied Science at the University of Pennsylvania and supported by the National Science Foundation (ECCS-1842655, DMR-2019444). Additional support came from the Natural Sciences and Engineering Research Council of Canada, through a Ph.D. Scholarship awarded to Ouellet and IBM as part of a doctorate. Scholarship awarded to Breitweiser.
Other co-authors include Tzu-Yung Huang, a former ESE doctoral student at Penn Engineering, now at Nokia Bell Labs, and Tim H. Taminiau of Delft University of Technology.