Negatively charged nitrogen-vacancy (NV${}^{\ensuremath{-}}$) centers in diamond have generated much recent interest for their use in sensing. The sensitivity improves when the NV ground-state microwave transitions are narrow, but these transitions suffer from inhomogeneous broadening, especially in high-density NV ensembles. To better understand and remove the sources of broadening, we demonstrate room-temperature spectral ``hole burning'' of the NV ground-state transitions. We find that hole burning removes the broadening caused by magnetic fields from ${}^{13}$C nuclei and demonstrate that it can be used for magnetic-field-insensitive thermometry.
Negatively charged nitrogen-vacancy (NV\ensuremath−) centers in diamond have generated much recent interest for their use in sensing. The sensitivity improves when the NV ground-state microwave transitions are narrow, but these transitions suffer from inhomogeneous broadening, especially in high-density NV ensembles. To better understand and remove the sources of broadening, we demonstrate room-temperature spectral ``hole burning'' of the NV ground-state transitions. We find that hole burning removes the broadening caused by magnetic fields from 13C nuclei and demonstrate that it can be used for magnetic-field-insensitive thermometry.
Nitrogen-vacancy (NV) defect centers in diamond have generated much interest for their uses in quantum information and sensing. Despite the ongoing improvements in sensitivity and the range of new applications, much about the NV basic physics remains unresolved, which is important to understand in order to fully exploit potential uses. In this work I describe a series of experiments on NV basic properties, applications, and projects in between. First, I describe an NV singlet absorption spectroscopy experiment, which searched for additional NV electronic states and studied the 1A1 phonon modes. Next, I discuss an NV microwave saturation spectroscopy experiment, which is useful for NV thermometry, removes inhomogeneous broadening, and can yield information about diamond magnetic spin bath dynamics. I then describe an NV relaxation experiment that senses GHz-frequency magnetic noise, which we demonstrated using paramagnetic substitutional nitrogen (P1) centers. Finally, I describe open questions on the NV singlet states, saturation spectroscopy, and relaxation (and how to address them), and report on my ongoing work on using NVs for nuclear polarization and rotation sensing.
Quantum relaxometry based on nitrogen-vacancy (NV) centers in diamond is an easy-to-use technique that detects magnetic noise by measuring the longitudinal relaxation of NV centers. It is favored in chemical and biological applications due to the robustness against imperfect spin control. By tuning the energy level, NV relaxometry can detect magnetic noise generated by other spins and obtain magnetic resonance spectra through cross relaxation. However, the inhomogeneous broadening of NV centers greatly limits the spectral resolution of cross-relaxation spectra. Here we demonstrate a hole-burning technique to remove the inhomogeneous broadening. We utilize a weak pump field to deplete specific NV centers during the relaxation measurement, which contribute a reverse signal in the cross-relaxation spectra with a much narrower linewidth. Our method retains the convenience and sensitivity of NV relaxometry, opening up new avenues for high-resolution magnetic resonance spectroscopy in complex scenarios.
We report measurements of optically detected magnetic resonance spectra of ensembles of nitrogen-vacancy (NV-) centers in diamonds in the presence of electromagnetic fields. To reduce inhomogeneous broadening, the spectra are acquired from a region of 20 cubic microns in a CVD(Chemical Vapor Deposition) diamond through a confocal microscope. The Stark shift from transverse electric fields is enhanced at avoided crossings between the hyperfine levels that arise from interaction with 14N(I = 1) nuclei in the diamond lattice. As expected from previous reports, the Stark shift of the spectral lines is stronger when there is no magnetic field along the NV axis. The shift is also strong, but for different transitions, at a field of about 100 uT.
We introduce a microwave-assisted spectroscopy technique to determine the relative ratio of fluorescence emitted by nitrogen-vacancy (N-V) centers in diamond that are negatively charged ($\mathrm{N}\text{\ensuremath{-}}{V}^{\ensuremath{-}}$) and neutrally charged ($\mathrm{N}\text{\ensuremath{-}}{V}^{0}$) and present its application to studying spin-dependent ionization in N-V ensembles and enhancing N-V-magnetometer sensitivity. Our technique is based on selectively modulating the $\mathrm{N}\text{\ensuremath{-}}{V}^{\ensuremath{-}}$ fluorescence with a spin-state-resonant microwave drive to isolate, in situ, the spectral shape of the $\mathrm{N}\text{\ensuremath{-}}{V}^{\ensuremath{-}}$ and $\mathrm{N}\text{\ensuremath{-}}{V}^{0}$ contributions to an N-V-ensemble sample's fluorescence. As well as serving as a reliable means to characterize the charge state, the method can be used as a tool to study spin-dependent ionization in N-V ensembles. As an example, we apply the microwave technique to a high-N-V-density diamond sample and find evidence for an additional spin-dependent ionization pathway, which we present here alongside a rate-equation model of the data. We further show that our method can be used to enhance the contrast of optically detected magnetic resonance (ODMR) on N-V ensembles and may lead to significant sensitivity gains in N-V magnetometers dominated by technical noise sources, especially where the $\mathrm{N}\text{\ensuremath{-}}{V}^{0}$ population is large. With the high-N-V-density diamond sample investigated here, we demonstrate an up to 4.8-fold enhancement in the ODMR contrast. We also propose a second postprocessing method of increasing the ODMR contrast in shot-noise-limited applications. The techniques presented here may also be applied to other solid-state defects, as long as their fluorescence can be selectively modulated by means of a microwave drive. We demonstrate this utility by applying our method to isolate room-temperature spectral signatures of the V2-type silicon vacancy from an ensemble of V1 and V2 silicon vacancies in 4H silicon carbide.
Abstract With their optical addressability of individual spins and long coherence time, nitrogen-vacancy (NV) centers in diamond are often called “atom-like solid spin-defects”. As observed with trapped atomic ions, quantum interference mediated by indistinguishable photons was demonstrated between remote NV centers. In high sensitivity DC magnetometry at room temperature, NV ensembles are potentially rivaling with alkali-atom vapor cells. However, local strain induces center-to-center variation of both optical and spin transitions of NV centers. Therefore, advanced engineering of diamond growth toward crystalline perfection is demanded. Here, we report on the synthesis of high-quality HPHT (high-pressure, high-temperature) crystals, demonstrating a small inhomogeneous broadening of the spin transitions, of T 2 * = 1.28 μs, approaching the limit for crystals with natural 13 C abundance, that we determine as T 2 * = 1.48 μs. The contribution from strain and local charges to the inhomogeneous broadening is lowered to ~17 kHz full width at half maximum for NV ensemble within a > 10 mm 3 volume. Looking at optical transitions in low nitrogen crystals, we examine the variation of zero-phonon-line optical transition frequencies at low temperatures, showing a strain contribution below 2 GHz for a large fraction of single NV centers.
We propose a method to create a room-temperature maser operating at approximately 2.9~GHz frequency using an ensemble of negatively charged nitrogen-vacancy electronic spins (NV) in diamond, without requiring population inversion. Our method considers a DC magnetic field of a few milli-Tesla (mT) applied along the perpendicular direction of an ensemble of NV spins aligned along a common axis. This perpendicular magnetic-field creates superposition states of ∣ms=−1⟩ and ∣ms=+1⟩ of the NV spin's ground state triplet levels and thereby makes it possible to drive all three transitions in the NV spin ground state. We model the system by including optical pumping of the NV spins, near-resonant driving of two transitions, and coupling the third transition to a near-resonant microwave resonator. Numerical estimates using experimentally realizable parameters show that inversionless masing can be achieved inside the microwave resonator using our method. As an application, we show that the output intensity of an inversionless maser (1.1×1014 spins) can be used for magnetic field sensing with a DC sensitivity on the order of a hundred pT/Hz. Our study opens a new direction in room-temperature diamond NV maser devices for quantum technological applications without the requirement of a strong bias magnetic field, as in conventional NV diamond masers.