Nitrogen-vacancy (NV) centers in millimeter-scale diamond samples were produced by irradiation and subsequent annealing under varied conditions. The optical and spin relaxation properties of these samples were characterized using confocal microscopy, visible and infrared absorption, and optically detected magnetic resonance. The sample with the highest NV concentration, approximately 16 ppm (2.8 × 10 18 cm −3 ), was prepared with no observable traces of neutrally-charged vacancy defects. The eective transverse spin-relaxation time for this sample was T * 2 = 118(48) ns, predominately limited by residual paramagnetic nitrogen which was determined to have a concentration of 49(7) ppm. Under ideal conditions, the shot-noise limited sensitivity is projected to be ∼ 150 fT/ √ Hz for a 100 µm-scale magnetometer based on this sample. Other samples with NV concentrations from .007 to 12 ppm and eective relaxation times ranging from 27 to over 291 ns were prepared and characterized.

The temperature dependence of the magnetic-resonance spectra of nitrogen-vacancy (NV-) ensembles in the range of 280-330 K was studied. Four samples prepared under different conditions were analyzed with NV- concentrations ranging from 10 ppb to 15 ppm. For all samples, the axial zero-field splitting (ZFS) parameter D was found to vary significantly with temperature, T, as dD/dT=-74.2(7) kHz/K. The transverse ZFS parameter E was nonzero (between 4 and 11 MHz) in all samples, and exhibited a temperature dependence of dE/(EdT)=-1.4(3)x10{-4} K-1. The results might be accounted for by considering local thermal expansion. The temperature dependence of the ZFS parameters presents a significant challenge for diamond magnetometers and may ultimately limit their bandwidth and sensitivity.

We present an experimental study of the longitudinal electron-spin relaxation time (T1) of negatively charged nitrogen-vacancy (NV) ensembles in diamond. T1 was studied as a function of temperature from 5 to 475 K and magnetic field from 0 to 630 G for several samples with various NV and nitrogen concentrations. Our studies reveal three processes responsible for T1 relaxation. Above room temperature, a two-phonon Raman process dominates; below room temperature, we observe an Orbach-type process with an activation energy of 73(4) meV, which closely matches the local vibrational modes of the NV center. At yet lower temperatures, sample dependent cross-relaxation processes dominate, resulting in temperature independent values of T1 from milliseconds to minutes. The value of T1 in this limit depends sensitively on the magnetic field and can be tuned by more than 1 order of magnitude.

The zero-phonon transition rate of a nitrogen-vacancy center is enhanced by a factor of ∼ 70 by coupling to a photonic crystal resonator fabricated in monocrystalline diamond using standard semiconductor fabrication techniques. Photon correlation measurements on the spectrally filtered zero-phonon line show antibunching, a signature that the collected photoluminescence is emitted primarily by a single nitrogen-vacancy center. The linewidth of the coupled nitrogen-vacancy center and the spectral diffusion are characterized using high-resolution photoluminescence and photoluminescence excitation spectroscopy.Nitrogen-vacancy (NV) centers in diamond represent one of the best test-beds for future quantum photonic technologies [1, 2] due to their outstanding properties as spin qubits [3] that can be coupled to optical photons [4]. Applications include quantum information [5] and electro-magnetic field sensing [6][7][8]. For quantum information applications, multiple NV centers need to be interconnected. One approach relies on integrating NVs in photonic networks, where large-scale entanglement between NV centers is created using interference of identical photons at the zero-phonon line (ZPL) frequency. However, in bulk diamond the ZPL transition accounts for only a few percent of the NV emission. Here we report ∼ 70 fold enhancement of the transition rate through the ZPL for a single NV coupled to a photonic crystal cavity in monocrystalline diamond. These cavities are fabricated using scalable semiconductor fabrication techniques and can be further coupled into photonic networks [2].The spontaneous emission rate enhancement of a particular dipole transition i of an emitter coupled to a microresonator relative to the uniform dielectric medium of the resonator is enhanced by the factor τ0where 1/τ 0 is the emission rate in the uniform dielectric medium, 1/τ leak is the emission rate outside the cavity mode, and