We show that the orientation of nitrogen-vacancy (NV) defects in diamond can be efficiently controlled through chemical vapor deposition (CVD) growth on a (111)-oriented diamond substrate. More precisely, we demonstrate that spontaneously generated N
V defects are oriented with a ~ 97 % probability along the [111] axis, corresponding to the most appealing orientation among the four possible crystallographic axes. Such a nearly perfect preferential orientation is explained by analyzing the diamond growth mechanism on a (111)-oriented substrate and could be extended to other types of defects. This work is a significant step towards the design of optimized diamond samples for quantum information and sensing applications.
We employ a scanning NV-center microscope to perform stray field imaging of bubble magnetic domains in a perpendicularly magnetized Pt/Co/AlOx trilayer with 6 {AA} of Co. The stray field created by the domain walls is quantitatively mapped with few-n
anometer spatial resolution, with a probe-sample distance of about 100 nm. As an example of application, we show that it should be possible to determine the Bloch or Neel nature of the domain walls, which is of crucial importance to the understanding of current-controlled domain wall motion.
Thin-film ferromagnetic disks present a vortex spin structure whose dynamics, added to the small size (~10 nm) of their core, earned them intensive study. Here we use a scanning nitrogen-vacancy (NV) center microscope to quantitatively map the stray
magnetic field above a 1 micron-diameter disk of permalloy, unambiguously revealing the vortex core. Analysis of both probe-to-sample distance and tip motion effects through stroboscopic measurements, allows us to compare directly our quantitative images to micromagnetic simulations of an ideal structure. Slight perturbations with respect to the perfect vortex structure are clearly detected either due to an applied in-plane magnetic field or imperfections of the magnetic structures. This work demonstrates the potential of scanning NV microscopy to map tiny stray field variations from nanostructures, providing a nanoscale, non-perturbative detection of their magnetic texture.
We report an experimental study of the longitudinal relaxation time ($T_1$) of the electron spin associated with single nitrogen-vacancy (NV) defects hosted in nanodiamonds (ND). We first show that $T_1$ decreases over three orders of magnitude when
the ND size is reduced from 100 to 10 nm owing to the interaction of the NV electron spin with a bath of paramagnetic centers lying on the ND surface. We next tune the magnetic environment by decorating the ND surface with Gd$^{3+}$ ions and observe an efficient $T_{1}$-quenching, which demonstrates magnetic noise sensing with a single electron spin. We estimate a sensitivity down to $approx 14$ electron spins detected within 10 s, using a single NV defect hosted in a 10-nm-size ND. These results pave the way towards $T_1$-based nanoscale imaging of the spin density in biological samples.
We use the electronic spin of a single Nitrogen-Vacancy (NV) defect in diamond to observe the real-time evolution of neighboring single nuclear spins under ambient conditions. Using a diamond sample with a natural abundance of $^{13}$C isotopes, we f
irst demonstrate high fidelity initialization and single-shot readout of an individual $^{13}$C nuclear spin. By including the intrinsic $^{14}$N nuclear spin of the NV defect in the quantum register, we then report the simultaneous observation of quantum jumps linked to both nuclear spin species, providing an efficient initialization of the two qubits. These results open up new avenues for diamond-based quantum information processing including active feedback in quantum error correction protocols and tests of quantum correlations with solid-state single spins at room temperature.
Magnetometry and magnetic imaging with nitrogen-vacancy (NV) defects in diamond rely on the optical detection of electron spin resonance (ESR). However, this technique is inherently limited to magnetic fields that are weak enough to avoid electron sp
in mixing. Here we focus on the high off-axis magnetic field regime for which spin mixing alters the NV defect spin dynamics. We first study in a quantitative manner the dependence of the NV defect optical properties on the magnetic field vector B. Magnetic-field-dependent time-resolved photoluminescence (PL) measurements are compared to a seven-level model of the NV defect that accounts for field-induced spin mixing. The model reproduces the decreases in (i) ESR contrast, (ii) PL intensity and (iii) excited level lifetime with an increasing off-axis magnetic field. We next demonstrate that those effects can be used to perform all-optical magnetic imaging in the high off-axis magnetic field regime. Using a scanning NV defect microscope, we map the stray field of a magnetic hard disk through both PL and fluorescence lifetime imaging. This all-optical method for high magnetic field imaging at the nanoscale might be of interest in the field of nanomagnetism, where samples producing fields in excess of several tens of milliteslas are typical.
We report a systematic study of the hyperfine interaction between the electron spin of a single nitrogen-vacancy (NV) defect in diamond and nearby $^{13}$C nuclear spins, by using pulsed electron spin resonance spectroscopy. We isolate a set of discr
ete values of the hyperfine coupling strength ranging from 14 MHz to 400 kHz and corresponding to $^{13}$C nuclear spins placed at different lattice sites of the diamond matrix. For each lattice site, the hyperfine interaction is further investigated through nuclear spin polarization measurements and by studying the magnetic field dependence of the hyperfine splitting. This work provides informations that are relevant for the development of nuclear-spin based quantum register in diamond.
We show that a dimer made of two gold nanospheres exhibits a remarkable efficiency for second-harmonic generation under femtosecond optical excitation. The detectable nonlinear emission for the given particle size and excitation wavelength arises whe
n the two nanoparticles are as close as possible to contact, as in situ controlled and measured using the tip of an atomic force microscope. The excitation wavelength dependence of the second-harmonic signal supports a coupled plasmon resonance origin with radiation from the dimer gap. This nanometer-size light source might be used for high-resolution near-field optical microscopy.
We report a systematic study of the magnetic field sensitivity of a magnetic sensor based on a single Nitrogen-Vacancy (NV) defect in diamond, by using continuous optically detected electron spin resonance (ESR) spectroscopy. We first investigate the
behavior of the ESR contrast and linewidth as a function of the microwave and optical pumping power. The experimental results are in good agreement with a simplified model of the NV defect spin dynamics, yielding to an optimized sensitivity around 2 mu T/sqrt{rm Hz}. We then demonstrate an enhancement of the magnetic sensitivity by one order of magnitude by using a simple pulsed-ESR scheme. This technique is based on repetitive excitation of the NV defect with a resonant microwave pi-pulse followed by an optimized read-out laser pulse, allowing to fully eliminate power broadening of the ESR linewidth. The achieved sensitivity is similar to the one obtained by using Ramsey-type sequences, which is the optimal magnetic field sensitivity for the detection of DC magnetic fields.
We present a study of the charge state conversion of single nitrogen-vacancy (NV) defects hosted in nanodiamonds (NDs). We first show that the proportion of negatively-charged NV$^{-}$ defects, with respect to its neutral counterpart NV$^{0}$, decrea
ses with the size of the ND. We then propose a simple model based on a layer of electron traps located at the ND surface which is in good agreement with the recorded statistics. By using thermal oxidation to remove the shell of amorphous carbon around the NDs, we demonstrate a significant increase of the proportion of NV$^{-}$ defects in 10-nm NDs. These results are invaluable for further understanding, control and use of the unique properties of negatively-charged NV defects in diamond
