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Register a new userOptically Detected Magnetic Resonances of Nitrogen-Vacancy Ensembles in 13C Enriched Diamond
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We present an experimental and theoretical study of the optically detected magnetic resonance signals for ensembles of negatively charged nitrogen-vacancy (NV) centers in 13C isotopically enriched single-crystal diamond. We observe four broad transition peaks with superimposed sharp features at zero magnetic field and study their dependence on applied magnetic field. A theoretical model that reproduces all qualitative features of these spectra is developed. Understanding the magnetic-resonance spectra of NV centers in isotopically enriched diamond is important for emerging applications in nuclear magnetic resonance.
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In this paper cross-relaxation between nitrogen-vacancy (NV) centers and substitutional nitrogen in a diamond crystal was studied. It was demonstrated that optically detected magnetic resonance signals (ODMR) can be used to measure these signals successfully. The ODMR were detected at axial magnetic field values around 51.2~mT in a diamond sample with a relatively high (200~ppm) nitrogen concentration. We observed transitions that involve magnetic sublevels that are split by the hyperfine interaction. Microwaves in the frequency ranges from 1.3 GHz to 1.6 GHz ($m_S=0longrightarrow m_S=-1$ NV transitions) and from 4.1 to 4.6 GHz ($m_S=0longrightarrow m_S=+1$ NV transitions) were used. To understand the cross-relaxation process in more detail and, as a result, reproduce measured signals more accurately, a model was developed that describes the microwave-initiated transitions between hyperfine levels of the NV center that are undergoing anti-crossing and are strongly mixed in the applied magnetic field. Additionally, we simulated the extent to which the microwave radiation used to induce ODMR in the NV center also induced transitions in the substitutional nitrogen via cross-relaxation. The improved understanding of the NV processes in the presence of a magnetic field will be useful for designing NV-diamond-based devices for a wide range of applications from implementation of q-bits to hyperpolarization of large molecules to various quantum technological applications such as field sensors.
Nitrogen-vacancy (NV) centers in diamond have shown promise as inherently localized electric-field sensors, capable of detecting individual charges with nanometer resolution. Working with NV ensembles, we demonstrate that a detailed understanding of the internal electric field environment enables enhanced sensitivity in the detection of external electric fields. We follow this logic along two complementary paths. First, using excitation tuned near the NVs zero-phonon line, we perform optically detected magnetic resonance (ODMR) spectroscopy at cryogenic temperatures in order to precisely measure the NV centers excited-state susceptibility to electric fields. In doing so, we demonstrate that the characteristically observed contrast inversion arises from an interplay between spin-selective optical pumping and the NV centers local charge distribution. Second, motivated by this understanding, we propose and analyze a novel scheme for optically-enhanced electric-field sensing using NV ensembles; we estimate that our approach should enable order of magnitude improvements in the DC electric-field sensitivity.
We report electrical tuning by the Stark effect of the excited-state structure of single nitrogen-vacancy (NV) centers located less than ~100 nm from the diamond surface. The zero-phonon line (ZPL) emission frequency is controllably varied over a range of 300 GHz. Using high-resolution emission spectroscopy, we observe electrical tuning of the strengths of both cycling and spin-altering transitions. Under resonant excitation, we apply dynamic feedback to stabilize the ZPL frequency. The transition is locked over several minutes and drifts of the peak position on timescales greater than ~100 ms are reduced to a fraction of the single-scan linewidth, with standard deviation as low as 16 MHz (obtained for an NV in bulk, ultra-pure diamond). These techniques should improve the entanglement success probability in quantum communications protocols.
We give instructions for the construction and operation of a simple apparatus for performing optically detected magnetic resonance measurements on diamond samples containing high concentrations of nitrogen-vacancy (NV) centers. Each NV center has a spin degree of freedom that can be manipulated and monitored by a combination of visible and microwave radiation. We observe Zeeman shifts in the presence of small external magnetic fields and describe a simple method to optically measure magnetic field strengths with a spatial resolution of several microns. The activities described are suitable for use in an advanced undergraduate lab course, powerfully connecting core quantum concepts to cutting edge applications. An even simpler setup, appropriate for use in more introductory settings, is also presented.
We report a study of the magnetic field dependence of the photo-luminescence of NV$^-$ centers (negatively charged nitrogen-vacancy centers) in diamond single crystals. In such a magnetic field dependence characteristic lines are observed, which are coming from Level Anti-Crossings (LACs) in the coupled electron-nuclear spin system. For enhancing the sensitivity, we used lock-in detection to measure the photo-luminescence intensity and observed a remarkably strong dependence of the LAC-derived lines on the modulation frequency. Upon decreasing of the modulation frequency from 12 kHz to 17 Hz the amplitude of the lines increases by approximately two orders of magnitude. To take a quantitative account for such effects, we developed a theoretical model, which describes the spin dynamics in the coupled electron-nuclear spin system under the action of an oscillating external magnetic field. Good agreement between experiments and theory allows us to conclude that the observed effects are originating from coherent spin polarization exchange in the NV$^-$ center. Our results are of great practical importance allowing one to optimize the experimental conditions for probing LAC-derived lines in diamond defect centers.
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