A groundbreaking theoretical study from researchers at the University of Chicago and Argonne National Laboratory has shed light on the microscopic mechanisms by which diamond surfaces influence the quantum coherence of nitrogen-vacancy (NV) centers. These NV centers are defects within diamonds known for their critical role in developing today’s highly sensitive quantum sensors. The findings have been published in the journal Physical Review Materials, where it has been designated as an Editors’ Suggestion paper due to its significance.
Giulia Galli, a professor at the University of Chicago Pritzker School of Molecular Engineering and senior scientist at Argonne National Laboratory, highlighted a longstanding dilemma in the field—why shallow NV centers experience rapid coherence loss. The research employed sophisticated surface models combined with quantum dynamics simulations to reveal that the source of decoherence is not merely determined by the types of spins on the diamond surface, but furthermore depends on their movement, illustrating that the noise associated with the surface is dynamic in nature.
This study is expected to offer clear, physics-based guidance on how to engineer diamond surfaces that enhance quantum coherence, which is essential for quantum sensing and the advancement of quantum information technologies. NV centers are notable for their ability to be manipulated and monitored optically at room temperature, enabling them to detect weak magnetic and electric fields from various substances, including biological systems. However, being in close proximity to the diamond surface subjects them to surface-induced noise, which can significantly degrade their performance.
Jonah Nagura, a Ph.D. candidate at UChicago PME and the lead author of the study, elaborated on how previous literature referred to the sources of this surface noise as “X spins” or “dark spins,” mainly because the specific details of the noise’s origin were not well-understood. This study offers clarity by pinpointing the noise sources and proposes methods to mitigate them, thereby paving the way for more advanced quantum sensors.
The researchers utilized density functional theory-based models and advanced quantum decoherence simulations to isolate and identify the main contributors to surface noise. Their findings indicated that surface defects, such as dangling bonds that can host unpaired electrons, create fluctuating magnetic noise that diminishes the coherence of NV centers, hindering their signal detection capabilities.
Importantly, the research indicates that the chemical termination of the surface significantly impacts NV coherence. The study reveals that surfaces terminated with oxygen or nitrogen maintain coherence akin to that of bulk material, even for NV centers located just a few nanometers beneath the surface. Conversely, surfaces terminated with hydrogen or fluorine generate intensified magnetic noise that can severely shorten coherence times.
The researchers concluded that the predominant factors affecting the coherence of shallow NV centers involve surface-electron relaxation and hopping. These electron spins interact with the laser pulses that manipulate and read NV states, causing variations that lead to increased noise.
By uncovering the leading microscopic noise channels, this research provides a comprehensive roadmap for the enhancement of NV-based quantum technologies, directly influencing advancements in quantum sensing and processing.
In summation, the progress made in understanding and mitigating surface-induced decoherence promises significant contributions to the development of efficient quantum sensors and information systems, harnessing the unique properties of diamonds for future technological innovations.