A new theoretical study led by researchers at the University of Chicago and Argonne National Laboratory has identified the microscopic mechanisms by which diamond surfaces affect the quantum coherence of nitrogen-vacancy (NV) centers — defects in diamond that underpin some of today’s most sensitive quantum sensors.
The study has appeared in Physical Review Materials and was selected to be an Editors' Suggestion paper.
“One long-standing challenge has been understanding why shallow NV centers lose coherence so quickly,” said Giulia Galli , professor at the University of Chicago Pritzker School of Molecular Engineering (UChicago PME) and senior scientist at Argonne National Laboratory. “By combining first-principles surface models with quantum dynamics simulations, we understood that the culprit of decoherence is not just which spins live at the diamond surface, but how they move: surface noise is dynamical!”
The findings of the study provide clear, physics-based guidelines for engineering diamond surfaces that help preserve quantum coherence, a key requirement for quantum sensing and emerging quantum information technologies.
NV centers are atomic-scale defects in diamond whose quantum spin states can be initialized, controlled, and read out optically at room temperature. When placed close to a diamond surface, NV centers can detect extremely weak magnetic and electric signals from molecules, materials, and biological systems. Yet this proximity also exposes them to surface-related noise, such as fluctuating paramagnetic defects and charge or electric-field noise, that rapidly degrades their quantum coherence and limits sensor performance.
“In the literature the origins of surface noise have been often called ‘X spins’ or ‘dark spins’, because the precise microscopic nature of the noise was not understood, and it may stem from optically inactive sites” said UChicago PME PhD candidate Jonah Nagura, lead author of the study. “Our research helps pinpoint exactly what is noisy at the surface and sets a path for eliminating the noise so that one can create more advanced, powerful quantum sensors.”
In this work, the researchers combined density functional theory-based atomistic models of diamond surfaces with advanced quantum decoherence simulations to identify and isolate the dominant surface noise mechanisms.
“During the fabrication process of diamond surfaces for sensing applications, undesired surface defects may be created, including what we call dangling bonds,” Nagura said. “Some of these defects can host unpaired-electrons, paramagnetic spins that fluctuate over time and generate magnetic noise that perturbs the NV center. That noise can reduce the NV’s coherence and can obscure the weak target signals that one wants to measure.”
The study shows that the way the surface is chemically terminated, has a profound impact on NV coherence. Nagura’s calculations showed that oxygen- and nitrogen-terminated surfaces largely preserve near-bulk coherence even for NV centers only a few nanometers below the surface. By contrast, hydrogen- and fluorine-terminated surfaces introduce much stronger surface-related magnetic noise, which drastically shortens coherence times.
“However, while termination chemistry and facet orientation do matter, we found that it is surface-electron relaxation and hopping that dominate the coherence of shallow NVs,” Nagura said. “The electron spins present at the surface interact with the same laser pulses that are used to manipulate and read out the NV center. The laser light can drive changes in the surface charge state, causing unpaired electrons to hop between different atomic sites. That motion produces additional time-varying magnetic fields, that in turn generates extra noise.”
By identifying the dominant microscopic noise channels, the study provides a roadmap for improving NV-based quantum devices, with direct implications for quantum sensing and information processing.
“Once we account for electron motion at the surface, theory and experiment finally line up,” Nagura said.
Physical Review Materials
Understanding surface-induced decoherence of NV centers in diamond
5-Feb-2026