Abstract
Understanding the dynamics of a quantum bit’s environment is essential for the realization of practical systems for quantum information processing and metrology. We use single nitrogen-vacancy (NV) centers in diamond to study the dynamics of a disordered spin ensemble at the diamond surface. Specifically, we reduce the density of “dark” surface spins to interrogate their contribution to the decoherence of shallow NV center spin qubits. When the average surface spin spacing exceeds the NV center depth, we find that the surface spin contribution to the NV center free induction decay can be described by a stretched exponential with variable power . We show that these observations are consistent with a model in which the spatial positions of the surface spins are fixed for each measurement, but some of them reconfigure between measurements. In particular, we observe a depth-dependent critical time associated with a dynamical transition from Gaussian () decay to , and show that this transition arises from the competition between the small decay contributions of many distant spins and strong coupling to a few proximal spins at the surface. These observations demonstrate the potential of a local sensor for understanding complex systems and elucidate pathways for improving and controlling spin qubits at the surface.
15 More- Received 24 March 2022
- Revised 27 June 2022
- Accepted 6 October 2022
DOI:https://doi.org/10.1103/PRXQuantum.3.040328
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Viewpoint
Spin-Interaction Studies Take on a New Dimension
Published 3 January 2023
Studies of how a nitrogen-vacancy center’s spin interacts with a surrounding 2D layer of spins could lead to new platforms for quantum metrology and simulation.
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Popular Summary
Atomic defects in diamond known as color centers are promising candidates for a host of quantum information and sensing technologies. For nanoscale sensing applications, these defects must be located next to the sensing target, which necessitates creating these defects near the diamond surface, where they can be overwhelmed by surface-related noise sources. Understanding the nature of this surface noise is thus an important step toward improving sensing technologies based on these color centers.
One class of surface defects is unpaired electron spins that are present in nearly all diamond samples. By measuring the effect these surface spins have on over 100 nitrogen-vacancy (NV) centers across many diamond samples, we gain insight into the dynamic nature of these surface spins and resolve some longstanding mysteries. In particular, we find that their coupling statistics and the shape of the coherence decay curve are inconsistent with static spatial arrangements of spins on the diamond surface, and instead are consistent with the surface spins spatially reconfiguring in time. In the very dilute limit, the shape of the NV center coherence decay exhibits an abrupt transition at a critical time that corresponds to the distance between the NV center and the surface spin bath.
We show that detailed analysis of NV center coherence can be used as a powerful probe of the dynamics of the environment, and our experiments help pave the way for potential techniques to mitigate surface noise and harness local quantum sensors to study many-body dynamics.