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arXiv:1505.02253 · EPJ Quantum Technology

Longitudinal spin relaxation in nitrogen-vacancy ensembles in diamond

Mariusz Mrózek, Daniel Rudnicki, Pauli Kehayias, Andrey Jarmola, Dmitry Budker, Wojciech Gawlik

Published Oct 29, 2015• 88 citations
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Abstract

We present an experimental study of the longitudinal electron-spin relaxation of ensembles of negatively charged nitrogen-vacancy (NV−) centers in diamond. The measurements were performed with samples having different NV− concentrations and at different temperatures and magnetic fields. We found that the relaxation rate $T_{1}^{-1}$ increases when transition frequencies in NV− centers with different orientations become degenerate and interpret this as cross-relaxation caused by dipole-dipole interaction.

DOI
10.1140/epjqt/s40507-015-0035-z

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We present an experimental study of the longitudinal electron-spin relaxation of ensembles of negatively charged nitrogen-vacancy (NV−) centers in diamond. The measurements were performed with samples having different NV− concentrations and at different temperatures and magnetic fields. We found that the relaxation rate T1−1T_{1}^{-1}T1−1​ increases when transition frequencies in NV− centers with different orientations become degenerate and interpret this as cross-relaxation caused by dipole-dipole interaction.
We study cross-relaxation-based magnetometry in ensembles of nitrogen-vacancy (NV) centers using the protocol suggested by Akhmedzhanov et al. [R. Akhmedzhanov, L. Gushchin, N. Nizov, V. Nizov, D. Sobgayda, I. Zelensky, and P. Hemmer, Microwave-free magnetometry based on cross-relaxation resonances in diamond nitrogen-vacancy centers, Phys. Rev. A 96, 013806 (2017)]. We suggest a processing scheme that allows us to perform measurements without precise sample orientation. It is shown theoretically and experimentally that using an additional magnetic field can significantly simplify vector magnetic-field measurements.
We investigated spin-echo coherence times T2 of negatively charged nitrogen vacancy center (NV−) ensembles in single-crystalline diamond synthesized by either the high-pressure and high-temperature and chemical vapor deposition methods. This study specifically examined the magnetic dipole–dipole interaction (DDI) from the various electronic spin baths, which are the source of T2 decoherence. Diamond samples with NV− center concentration [NV−] comparable to those of neutral substitutional nitrogen concentration [Ns0] were used for DDI estimation. Results show that the T2 of the ensemble NV− center decreased in inverse proportion to the concentration of nitrogen-related paramagnetic defects [NPM], being the sum of [Ns0], [NV−], and [NV0], which is a neutrally charged state NV center. This inversely proportional relation between T2 and [NPM] indicates that the nitrogen-related paramagnetic defects of three kinds are the main decoherence source of the ensemble NV− center in the single-crystalline diamond. We found that the DDI coefficient of NVH− center was significantly smaller than that of Ns0, the NV0 center, or the NV− center. We ascertained the DDI coefficient of the NV− center DNV− through experimentation using a linear summation of the decoherence rates of each nitrogen-related paramagnetic defect. The obtained value of 89 μs ppm for DNV− corresponds well to the value estimated from the relation between DDI coefficient and spin multiplicity.
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.
Spin-lattice relaxation within the nitrogen-vacancy (NV) center's electronic ground-state spin triplet limits its coherence times, and thereby impacts its performance in quantum applications. We report measurements of the relaxation rates on the NV center's |m_{s}=0⟩↔|m_{s}=±1⟩ and |m_{s}=-1⟩↔|m_{s}=+1⟩ transitions as a function of temperature from 9 to 474 K in high-purity samples. We show that the temperature dependencies of the rates are reproduced by an ab initio theory of Raman scattering due to second-order spin-phonon interactions, and we discuss the applicability of the theory to other spin systems. Using a novel analytical model based on these results, we suggest that the high-temperature behavior of NV spin-lattice relaxation is dominated by interactions with two groups of quasilocalized phonons centered at 68.2(17) and 167(12) meV.
The nitrogen vacancy (NV) center in diamond is promising as an electron spin qubit due to its long-lived coherence and optical addressability. The ground state is a spin triplet with two levels $({m}_{s}=\ifmmode\pm\else\textpm\fi{}1)$ degenerate at zero magnetic field. Polarization-selective microwave excitation is an attractive method to address the spin transitions independently since this allows operation down to zero magnetic field. Using a resonator designed to produce circularly polarized microwaves, we have investigated the polarization selection rules of the NV center. We first apply this technique to NV ensembles in [100]- and [111]-oriented samples. Next, we demonstrate an imaging technique, based on optical polarization dependence, which allows rapid identification of the orientations of many single NV centers. Finally, we test the microwave polarization selection rules of individual NV centers of known orientation.
Understanding the limits to the spin coherence of the nitrogen-vacancy (NV) center in diamond is vital to realizing the full potential of this quantum system.We show that relaxation on the |m s = -1 ↔ |m s = +1 transition occurs approximately twice as fast as relaxation on the |m s = 0 ↔ |m s = ±1 transitions under ambient conditions in native NVs in high-purity bulk diamond.The rates we observe are independent of NV concentration over four orders of magnitude, indicating they are limited by spin-phonon interactions.We find that the maximum theoretically achievable coherence time for an NV at 295 K is limited to 6.8(2) ms.Finally, we present a theoretical analysis of our results that suggests Orbach-like relaxation from quasilocalized phonons or contributions due to higher-order terms in the spin-phonon Hamiltonian are the dominant mechanism behind |m s = -1 ↔ |m s = +1 relaxation, motivating future measurements of the temperature dependence of this relaxation rate.