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arXiv:2505.23512 · Physical review. B./Physical review. B

Extending and measuring dephasing times of nuclear spins in NV centers of diamond

Jingfu Zhang, Swathi S. Hegde, Fedor Jelezko, Dieter Suter

Published Aug 17, 2026• 0 citations
arXivHTMLPDF

Abstract

Long coherence times rank among the most important performance measures for many different types of quantum technology. In the electron-nuclear spin system of NV centers of diamond, the nuclear spins provide particularly long dephasing times. However, since initialization and readout require assistance from the electron spin, the apparent dephasing times can be reduced by the electron spin lifetime. Here we propose and implement schemes for measuring and extending the dephasing times of nuclear spins, resulting in dephasing times that are longer than the longitudinal relaxation time T 1 of the electron spin.

DOI
10.1103/c1ng-bsnr

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Long coherence times rank among the most important performance measures for many different types of quantum technology. In the electron-nuclear spin system of NV centers of diamond, the nuclear spins provide particularly long dephasing times. However, since initialization and readout require assistance from the electron spin, the apparent dephasing times can be reduced by the electron spin lifetime. Here we propose and implement schemes for measuring and extending the dephasing times of nuclear spins, resulting in dephasing times that are longer than the longitudinal relaxation time T 1 of the electron spin.
Abstract Nitrogen-vacancy (NV) center ensembles in diamond are one of the most promising solid-state quantum platforms for various sensing applications. Achieving ultimate sensitivity requires simultaneously long spin dephasing times ( T2∗{T}_{2}^{* }T2∗​ T 2 * ) and high NV center concentrations. In this work, we propose a systematic measurement approach to quantify the electron spin dephasing in NV center ensembles and analyze the contributions of various sources to the dephasing time, including NV-NV interactions, strain and electric field distributions, 13 C nuclear spins, and P1 electron spins. Our method is validated using a series of high-performance diamond samples, providing a comprehensive understanding of dephasing mechanisms and revealing correlations between NV concentration and different dephasing sources. Building on these insights, we outline strategies to further enhance the achievable sensitivity for DC magnetic field measurements.
A negatively-charged nitrogen-vacancy (NV) center in diamond is a promising system for quantum computation and quantum information. It has the diamond structure with a substitutional nitrogen atom and a neighboring vacancy. An electron spin in the NV center has an exceptionally long coherence time at room temperature. Thus the NV center has a potential to realize a room-temperature quantum computer which is more efficient than a classical computer. In this dissertation, we focus on the nitrogen nuclear spin as well as the electron spin in the NV center. Every NV center has the nitrogen nuclear spin. Because of the long coherence time of the nitrogen nuclear spin, it is a good candidate for a quantum memory. Thus it is important to prepare the nitrogen nuclear spin qubit in a given pure state for quantum computation. We provide a theoretical understanding of the popular nuclear spin initialization technique. Furthermore, we propose an optimal condition for the initialization of the nitrogen nuclear spin by including the local strain in the NV center. We expect that this optimal condition can improve the purity of the nuclear spin initialization. We also propose an efficient quantum measurement protocol for the hyperfine interaction between the electron spin and the ¹⁵N nuclear spin in the NV center. A precise knowledge of the hyperfine interaction is important to reduce an error in a coherent control of the ¹⁵N nuclear spin. In this protocol, a sequence of quantum operations with successively increasing duration is utilized to estimate the hyperfine interaction with successively higher precision approaching the quantum metrology limit. Unlike common quantum metrological methods, this protocol does not need the preparation of the nuclear spin in a pure state. In the presence of realistic operation errors and electron spin decoherence, we show the overall precision of our protocol still surpasses the standard quantum limit
Nitrogen-vacancy (NV) centers in diamond are a leading competitor for quantum sensing. The resolution of DC magnetic field sensing is limited by dephasing of the NV electron spin, with the main dephasing source being the thermal and quantum noise from the 13C^{13}\mathrm{C}13C nuclear spin bath. In this work, we propose an effective method to extend the dephasing time of a single NV electron spin by suppressing the nuclear spin noise. On the one hand, we improve the technique of bath driving to accommodate nuclear spin bath decoupling, and extend the dephasing time from 2.6 to 10.2 $\textmu{}\mathrm{s}$ at a magnetic field of 455 G. On the other hand, our method enables decoupling the quantum noise by inserting $\ensuremath{\pi}$ rotations around the ZZZ axis of the nuclear spin bath into the free evolution. By suppressing both the thermal and quantum noise, the dephasing time is extended by more than four times at 100 G. Our results provide a new route to explore strategies of suppressing the thermal noise and quantum noise in quantum information processing, and can be applied to other solid-state defects.
Abstract We demonstrate electrical detection of the 14 N nuclear spin coherence of NV centres at room temperature. Nuclear spins are candidates for quantum memories in quantum-information devices and quantum sensors, and hence the electrical detection of nuclear spin coherence is essential to develop and integrate such quantum devices. In the present study, we used a pulsed electrically detected electron-nuclear double resonance technique to measure the Rabi oscillations and coherence time ( T 2 ) of 14 N nuclear spins in NV centres at room temperature. We observed T 2 ≈ 0.9 ms at room temperature, however, this result should be taken as a lower limit due to limitations in the longitudinal relaxation time of the NV electron spins. Our results will pave the way for the development of novel electron- and nuclear-spin-based diamond quantum devices.
In recent years, NV centers in diamond has attracted significant attention as a candidate for quantum information devices. The negatively charged NV center, in particular, has been intensely investigated [1-3]. NV- centers host both an electron spin qubit and a nitrogen nuclear spin, in our case a nuclear spin-1/2 of 15N is imbedded. The ground state of the electron spin qubit has a long coherence time and an optical transition at 637nm. The nuclear spins may be considered as a long-lived quantum memory, which has been experimentally demonstrated [2]. Because of these preferable quantum properties, NV centers have been considered as a good candidate for implementation of quantum information processing and there has been a number of theoretically propose designs for quantum information processing [3].
Dynamical decoupling is a powerful technique for extending the coherence time ( T 2 ) of qubits. We apply this technique to the electron spin qubit of a single nitrogen-vacancy center in type-IIa diamond. In a crystal with natural abundance of 13 C nuclear spins, we extend the decoherence time up to 2.2 ms. This is close to the T 1 value of this NV center (4 ms). Since dynamical decoupling must perform well for arbitrary initial conditions, we measured the dependence on the initial state and compared the performance of different sequences with respect to initial state dependence and robustness to experimental imperfections.