Scientists at the University of Warwick have uncovered surprising “hot spots” around atomic defects in diamonds, challenging the long-held belief that diamonds are the ultimate natural heat conductors. This groundbreaking discovery could have significant implications for the design of diamond-based quantum technologies, such as ultra-precise sensors and future quantum computers.
Traditionally celebrated for their exceptional ability to conduct heat, diamonds have now been shown to briefly trap heat at the atomic scale in unexpected ways. The study, published in Physical Review Letters, reveals that when certain molecular-scale defects in diamond are excited with light, they create tiny, short-lived “hot spots” that momentarily distort the surrounding crystal structure.
Revolutionizing Diamond’s Role in Quantum Technologies
The research, conducted by scientists from the University of Warwick and their collaborators, focused on a specific atomic defect in diamond known as the Ns:H-C0 defect, where a nitrogen atom replaces a carbon atom and bonds with hydrogen. When the defect’s C-H bond was excited using ultrafast infrared laser pulses, researchers expected the heat to dissipate immediately into the diamond lattice. However, advanced spectroscopy revealed a different story.
Professor James Lloyd-Hughes from the Department of Physics at the University of Warwick explained,
“Finding a hot ground state for a molecular-scale defect in diamond was extremely surprising for us. Diamond is the best thermal conductor, so one would expect energy transport to prevent any such effect. However, at the nanoscale some phonons – packets of vibrational energy – hang around near the defect, creating a miniature hot environment that pushes on the defect itself.”
Exploring the Unexpected: Hot Ground States
The researchers observed that the defect briefly entered a ‘hot ground state’, meaning the surrounding crystal remained hot, altering the defect’s behavior. The presence of built-up vibrational energy nearby shifted the defect’s infrared signature to a higher energy, taking a few picoseconds to peak and then decay. This discovery was made possible through the use of multidimensional coherent spectroscopy (2DIR), a technique applied to diamond defects for the first time.
Dr. Junn Keat, a PDRA at the Department of Physics, University of Oxford, and former PhD student at Warwick, noted,
“This is the first time we’ve applied this technique to the study of diamond defects, and the direct observation of hot ground state formation was beyond our expectations. We are very pleased with the results of this novel approach and are excited to see what else we can study with this technique.”
Implications for Quantum Technologies
The study also delved into why diamonds fail to dissipate this energy instantly. The defect releases its energy by generating specific phonons with large energy, which do not travel far. These phonons move slowly and scatter quickly, creating a tiny bubble of heat around the defect before eventually decaying into faster-moving, heat-carrying vibrations.
Dr. Jiahui Zhao from the University of Warwick highlighted the significance of this phenomenon,
“Momentary local heating matters because defects are tiny, sensitive quantum systems, and even fleeting changes in their environment can affect their stability, precision, and usefulness in quantum technologies.”
Defects such as the nitrogen-vacancy (NV) and silicon-vacancy (SiV) centers in diamond are crucial for quantum information processing, serving as sensitive sensors and building blocks. Their performance heavily relies on maintaining stable spin states, which are strongly influenced by vibrations in the surrounding lattice.
Future Prospects and Challenges
The findings indicate that optical techniques used to control defects may inadvertently generate small, short-lived pockets of heat. These local temperature spikes can subtly disturb the spin states, potentially affecting coherence times and the overall performance of diamond-based quantum devices.
As the scientific community continues to explore the potential of diamond in quantum technologies, these new insights will play a pivotal role in refining techniques and improving the reliability of diamond-based components. The discovery of nanoscopic heat traps in diamonds not only challenges existing assumptions but also opens new avenues for research and innovation in the field of quantum technology.
