Researchers confirm spinning atomic nuclei exhibit quantum properties

Sydney, Australia (SPX) Feb 20, 2025
A groundbreaking study by researchers from the National University of Singapore (NUS) and the University of New South Wales (UNSW) Sydney has confirmed that spinning atomic nuclei indeed possess fundamental quantum properties. The collaborative work, led by Professor Valerio Scarani from NUS's Department of Physics and Scientia Professor Andrea Morello from UNSW Engineering, provides definitive proof of quantum behavior in nuclear spins. The study was published in the journal *Newton* on February 14, 2025.

For decades, physicists have inferred the quantum nature of subatomic particles like electrons and protons based on their response to magnetic fields. However, when allowed to spin freely, these particles seemingly behaved like classical spinning objects, such as a turning Wheel of Fortune. This assumption has been widely accepted in spin resonance studies for over 50 years.

Similarly, technicians operating Magnetic Resonance Imaging (MRI) machines have relied on this classical interpretation. In medical imaging, the spinning of protons within a patient generates a magnetic field similar to that produced by a fridge magnet rotating on an axis.

However, this new study challenges that perspective. Through an intricate single-atom measurement, researchers have demonstrated the unmistakable quantum nature of nuclear spins.

Unraveling the Mystery

Prof. Scarani, who also serves as Deputy Director of Singapore's Centre for Quantum Technologies (CQT), was inspired by a 15-year-old paper by Russian-Israeli mathematician Boris Tsirelson, which analyzed the probabilities of objects appearing at certain locations in rhythmic motion. Scarani theorized that these principles could be applied to the spinning behavior of quantum objects.

Working alongside his student, Mr. Zaw Lin Htoo, Scarani developed a hypothesis suggesting that under specific conditions, the quantum nature of an atomic nucleus could be definitively observed. To put this theory to the test, a collaboration with Prof. Morello's team at UNSW was established, utilizing highly precise measurement tools.

"For a single particle, it was widely believed that no measurable distinction existed between classical and quantum behavior," said Prof. Scarani.

Using an antimony nucleus, the UNSW team set the nucleus into motion and conducted precise rotational measurements. The experiment involved taking seven measurements per cycle to determine whether the nucleus aligned in a positive direction.

"In classical mechanics, the maximum probability for alignment in a given direction is four out of seven," Scarani explained. "However, quantum theory predicted that under special conditions, a higher probability could be observed. The deviation is small but statistically significant. Detecting this required precise, noise-free measurements."

Led by PhD student Mr. Arjen Vaartjes and Dr. Martin Nurizzo, the UNSW team successfully validated the quantum deviation, proving the theoretical predictions correct.

Challenging Conventional Knowledge

Prof. Morello expressed enthusiasm for overturning long-standing assumptions in physics. "This is fundamental science," he said. "It was previously believed that merely observing a nuclear spin's precession in a magnetic field couldn't confirm its quantum nature. Our results contradict that assumption."

The experiment utilized a special quantum state known as a 'Schrodinger cat state,' which carries distinct quantum properties. "By creating these unique nuclear spin states and observing their behavior, we have provided clear proof of their quantum nature," Morello added.

Implications for Quantum Science

Beyond its immediate scientific value, this discovery has broader implications for quantum technology. According to Prof. Scarani, "This experiment highlights the importance of specific quantum states in demonstrating fundamental principles. Such states could become valuable resources in quantum computing, making this method a reliable way to certify their creation."

With 2025 recognized by the United Nations as the International Year of Quantum Science and Technology-commemorating a century of quantum mechanics-Prof. Morello reflected on the significance of this discovery. "Quantum mechanics has been around for 100 years, yet we continue to make fundamental discoveries that reshape our understanding of the quantum world," he said.

"This work is less about immediate applications and more about intellectual beauty-an elegant observation of truth."

Research Report:Certifying the quantumness of a nuclear spin qudit through its uniform precession