We report a versatile method to polarize single nuclear spins in diamond, based on optical pumping of a single nitrogen-vacancy (NV) defect and mediated by a level anticrossing in its excited state. A nuclear-spin polarization higher than 98% is achieved at room temperature for the 15N nuclear spin associated with the NV center, corresponding to microK effective nuclear-spin temperature. We then show simultaneous initialization of two nuclear spins in the vicinity of a NV defect. Such robust control of nuclear-spin states is a key ingredient for further scaling up of nuclear-spin based quantum registers in diamond.
We report a versatile method to efficiently polarize single nuclear spins in diamond, which is based on optical pumping of a single NV color center and mediated by a level-anti crossing in its excited state. A nuclear spin polarization higher than 98% is achieved at room temperature for the 15N nuclear spin associated to the NV center, corresponding to
μK effective nuclear spin temperature. We then show simultaneous deterministic initialization of two nuclear spins (13C and 15N) in close vicinity to a NV defect. Such robust control of nuclear spin states is a key ingredient for further scaling up nuclear-spin based quantum registers in diamond.
Nuclear hyperpolarization from optically pumped color centers in solids offers an alternative to conventional microwave-driven dynamic nuclear polarization (DNP). Diamond can host the nitrogen vacancy (NV) center, whose ground spin state can be readily polarized by light at room temperature, making diamond a candidate platform for nuclear hyperpolarization. We report
13C nuclear hyperpolarization in randomly oriented diamond particles with sizes ranging from 0.2 to 2
μm, both at natural
13C abundance (1.1 %) and at 20 % isotopic enrichment, at magnetic fields of 7.1 T and 9.4 T. The protocol combines optical illumination with magic angle spinning (MAS) and does not require microwave irradiation. By investigating the nuclear polarization as a function of the MAS frequency between 0 and 6 kHz at the magnetic field of 7.1 T, we find maximum light-induced polarization enhancements of
280-fold for the isotopically enriched sample and
411-fold for the natural abundance sample. Under continuous illumination, steady-state absolute
13C polarization levels above 0.1 % are reached. A model involving optical pumping of NV centers and spin dynamics near level anticrossings (LACs) in three-spin clusters formed by NV, a substitutional nitrogen (P1) and
13C is used to describe these findings. The protocol strongly mitigates the effect of the anisotropy of the NV spin Hamiltonian, allowing more than
99.9% of NV orientations to participate in the polarization transfer process. These results represent a first step toward transferring nuclear polarization from diamond particles to external nuclei, with potential applications in sensitive and high-resolution NMR at room temperature.
Precision measurements based on optically detected nuclear magnetic resonance offer exquisite sensitivity to absolute shifts in spin transition frequencies, with potential applications in fundamental physics experiments and inertial sensing. We investigate 13C nuclear spins in diamond as a candidate system for solid-state implementations, which hold the promise for high-fidelity readout of large numbers of coherent nuclear spins in millitesla or lower magnetic fields. We demonstrate a technique that allows for both optical polarization and readout of large ensembles of ~10^{16} polarized nuclear spins. Our method takes advantage of state-selective Landau-Zener transitions under microwave frequency sweeping, which bidirectionally transfer spin polarization between Nitrogen-Vacancy (NV) electron spins and remote 13C nuclear spins. Using natural isotopic abundance diamonds with nitrogen densities of ~0.5-10 ppm, we perform optically-detected 13C Ramsey spectroscopy and realize a nuclear-spin-dependent fluorescence contrast exceeding 0.5% peak-to-peak. We observe nuclear spin dephasing times T2*~2 ms that only modestly improve with homonuclear dipolar decoupling, indicating that they are limited by the longitudinal spin relaxation of nearby NV electron spins. We study the magnetic field dependence of the optical readout and find comparable contrast and dephasing times for magnetic fields in the range 8-20 mT. Our method can be interpreted as a type of repetitive readout, where each NV center optically reads out the spin state of ~10^2 nuclei before nuclear spins depolarize.
Nitrogen vacancy (NV-) color centers in diamond are a prime candidate for use in quantum information devices, owing to their spin-1 ground state, straightforward optical initialization and readout, and long intrinsic coherence times in a room-temperature solid. While the 13C nuclear spin is often a dominant source of magnetic noise, we observe transitions between electron-nuclear hyperfine states of NV- centers in 99% 13C diamond that are robust to decoherence. At magnetic field strengths ranging from 550 - 900 G, these transitions are observable by optically detected magnetic resonance (ODMR), and exhibit linewidths narrowed by factors as high as ~130 at room temperature over typical electron-type transitions observed from this spin system. We anticipate the use of these decoherence-protected transitions, in combination with dynamical decoupling methods, for storage of quantum information.
In recent years, nitrogen-vacancy (NV) color centers in diamond have become excellent solid-state quantum sensors due to their electronic spin properties. Especially for their easy optical initialization and detection, together with their very large spin coherence at room temperature. Many studies have reported their use for sensing temperature, strain, electric fields, and mainly magnetic fields. Here, we show how to build a two-dimensional map of the electronic spin coherence of an ensemble of NV centers in ultra-pure diamond, using an optical imaging protocol combined with microwave pulses relying simply on a regular CCD camera.