Mona Jani

Quantum random number generation (QRNG) provides fundamentally unpredictable randomness derived from intrinsic quantum processes. In this work we demonstrate two solid-state, room-temperature QRNG implementations based on nitrogen-vacancy (NV) centers in diamond, i.e., ensemble fluorescence from nanodiamonds and single-photon emission from single NV centers located at the tips of fabricated diamond nanopillars for enhanced light collection efficiency, spatial isolation and minimized crosstalk. We compare entropy rates (above 0.98 bits), statistical performance, and robustness of both approaches in our experimental setup, the results contribute to establishing diamond-based QRNG as a scalable solution for quantum-secure randomness generation.

Biocompatible vaterite microspheres, renowned for their porous structure, are promising carriers for magnetic nanoparticles (MNPs) in biomedical applications such as targeted drug delivery and diagnostic imaging. Precise control over the magnetic moment of individual microspheres is crucial for these applications. This study employs widefield quantum diamond microscopy to map the stray magnetic fields of individual vaterite microspheres (3–10 μm) loaded with Fe₃O₄ MNPs of varying sizes (5 nm, 10 nm, and 20 nm). By analyzing over 35 microspheres under a 222 mT external magnetizing field, we measured peak-to-peak stray field amplitudes of 41 ± 1 μT for 5 nm and 10 nm superparamagnetic MNPs, reflecting their comparable magnetic response, and 12 ± 1 μT for 20 nm ferrimagnetic MNPs, due to distinct magnetization behavior. Finite-element simulations confirm variations in MNP distribution and magnetization uniformity within the vaterite matrix, with each microsphere encapsulating thousands of MNPs to generate its magnetization. This high-resolution magnetic imaging approach yields critical insights into MNP-loaded vaterite, enabling optimized synthesis and magnetically controlled systems for precision therapies and diagnostics.

Biocompatible vaterite microspheres, renowned for their porous structure, are promising carriers for magnetic nanoparticles (MNPs) in biomedical applications such as targeted drug delivery and diagnostic imaging. Precise control over the magnetic moment of individual microspheres is crucial for these applications. This study employs widefield quantum diamond microscopy to map the stray magnetic fields of individual vaterite microspheres (3-10 um) loaded with Fe3O4 MNPs of varying sizes (5 nm, 10 nm, and 20 nm). By analyzing over 35 microspheres under a 222 mT external magnetizing field, we measured peak-to-peak stray field amplitudes of 41 uT for 5 nm and 10 nm superparamagnetic MNPs, reflecting their comparable magnetic response, and 12 uT for 20 nm ferrimagnetic MNPs, due to distinct magnetization behavior. Finite-element simulations confirm variations in MNP distribution and magnetization uniformity within the vaterite matrix, with each microsphere encapsulating thousands of MNPs to generate its magnetization. This high-resolution magnetic imaging approach yields critical insights into MNP-loaded vaterite, enabling optimized synthesis and magnetically controlled systems for precision therapies and diagnostics.

Negatively charged nitrogen-vacancy (NV) diamond magnetometers are promising candidates for room-temperature magnetic field sensing. However, systematic studies of magnetic field sensors that evaluate the sensitivity of NV-diamond magnetometers as a function of multiple parameters are sparse. By comparing optically detected magnetic resonance (ODMR) dips for four single-crystal diamonds, we explored how the photon shot-noise-limited sensitivity and experimental magnetic noise floor were influenced by the density of the NV centers and methods of their formation. The lowest shot-noise-limited sensitivity was 380 pT √Hz⁻¹; it was significantly affected by ODMR fluorescence, contrast, and linewidth. Using dual-resonance modulation in ODMR, the experimental lowest magnetic noise floor based on power spectral density was 1.14 nT √Hz⁻¹. These values can be improved with an increase in laser power. This study will facilitate the selection of appropriate NV diamonds when designing magnetometers for various applications.

We implanted Fe+ ions in nanodiamond (ND) powder containing negatively charged nitrogen-vacancy (NV−) centers and studied their Raman spectra and optically detected magnetic resonance (ODMR) in various applied magnetic fields with green light (532 nm) excitation. In Raman spectra, we observed a blue shift of the NV− peak associated with the conversion of the electronic sp3 configuration to the disordered sp2 one typical for the carbon/graphite structure. In the ODMR spectra, we observed a red shift of the resonance position caused by local heating by an absorptive environment that recovers after annealing. To reveal the red shift mechanism in ODMR, we created a controlled absorptive environment around ND by adding iron-based Fe2O3 and graphitic sp2 powders to the ND suspension. This admixture caused a substantial increase in the observed shift proportional to the applied laser power, corresponding to an increase in the local temperature by 150–180 K. This surprisingly large shift is absent in non-irradiated NV-ND powders, is associated only with the modification of the local temperature by the absorptive environment of NV-NDs, and can be studied using ODMR signals of NV−.

We implanted Fe$^+$ ions in nanodiamond (ND) powder containing negatively charged nitrogen-vacancy (NV-) centers and studied their Raman spectra and optically detected magnetic resonance (ODMR) in various applied magnetic fields with green light (532 nm) excitation. In Raman spectra, we observed a blue shift of the NV$^-$ peak associated with the conversion of the electronic sp$^3$ configuration to the disordered sp$^2$ one typical for the carbon/graphite structure. In the ODMR spectra, we observed a red shift of the resonance position caused by local heating by an absorptive environment that recovers after annealing. To reveal the red shift mechanism in ODMR, we created a controlled absorptive environment around ND by adding iron-based Fe$_2$O$_3$ and graphitic sp$^2$ powders to the ND suspension. This admixture caused a substantial increase in the observed shift proportional to the applied laser power, corresponding to an increase in the local temperature by 150-180 K. This surprisingly large shift is absent in non-irradiated NV-ND powders, is associated only with the modification of the local temperature by the absorptive environment of NV-NDs and can be studied using ODMR signals of NV$^-$.

We demonstrate a photonic sensor of the magnetic fieldand itsgradients with remote readout. The sensor is based on optically detectedmagnetic resonance (ODMR) in nanodiamonds with nitrogen-vacancy colorcenters that are covalently attached as a thin film on one facet ofan optical fiber bundle. By measuring ODMR signals from a group ofindividual fibers in an & SIM;0.5-mm-wide imaging bundle, differencesof local magnetic field strengths and magnetic field gradients aredetermined across the plane of the bundle facet. The measured gradientsare created by direct electric currents flowing in a wire placed nearthe nanodiamond film. The measurement enabled the determination ofthe net magnetic field corresponding to various current directionsand their corresponding magnetic field gradients. This demonstrationopens up a perspective for compact fiber-based endoscopy, with additionalavenues for remote and sensitive magnetic field detection with submicrometerspatial resolution under ambient conditions.

A photoluminescence (PL) and Raman spectroscopy study of various diamond samples that have high concentrations of nitrogen‐vacancy (NV) color centers up to multiple parts per million (ppm) is presented. With green, red, and near‐infrared (NIR) light excitation, it is demonstrated that while for samples with a low density of NV centers the signals are primarily dominated by Raman scattering from the diamond lattice, for higher density of NVs, a combination of Raman scattering from the diamond lattice and fluorescence from the NV centers is observed, while for the highest NV densities the Raman signals from diamond are completely overwhelmed by the intense NV's fluorescence. However, under NIR excitation, Raman diamond signatures can be observed for some diamonds. These observations reveal different roles of two mechanisms of light emission and contradict the naïve belief that Raman scattering enables the complete characterization of a diamond crystalline sample.

By assembling 140 nm-sized fluorescent nanodiamonds (FNDs) in a thin-film on (3-aminopropyl) triethoxysilane functionalized glass surface, we prepare magnetically-sensitive FND-fiber probes for endoscopy. The obtained FND layers show good uniformity over large surfaces and are characterized using confocal, fluorescence, and atomic force microscopes. Further, FNDs are assembled on single large-core multimode optical fibers and imaging fiber bundles end face to detect optically detectable magnetic resonance (ODMR) signals. The ODMR signals are recorded through the fiber’s far end in magnetic fields between 0 to 2.5 mT. A multi-channel sensor is demonstrated with the capability of parallel-in-time mapping and instantaneous readout from individual pixel and enabling magnetic mapping at high spatial resolution. Results of this study are promising for early stage detection in bio-diagnostic applications.

Fluorescent nanodiamonds with nitrogen‐vacancy (NV) centers respond to local changes in electric and magnetic fields. These responses can be read optically as changes in fluorescence. NV centers do not suffer from photoblinking or photobleaching, making nanodiamonds a viable platform for long‐term imaging of processes inside living cells. However, for any bioapplication, the surface of these particles must be modified to prevent aggregation and nonspecific protein adsorption and to effectively transduce the changes in local environment to NV center. Modular biomimetic interface has been developed on nanodiamonds with remarkable sensitivity for relaxometric readout that takes advantage of self‐assembled phospholipid bilayers supported by the nanoparticle surface. This rapid and robust approach provides synthetic pathway to tunable composition, demonstrated by tuning surface charge and content of spin labels on nanodiamond. The supported phospholipid bilayer interface increases the detection sensitivity about one‐order‐of‐magnitude. Also, a theoretical model of the system is provided, which shows excellent agreement with experimental results. Merging biocompatibility, modularity, and outstanding spin sensitivity in one nanomaterial provides a foundation for development of multifunctional nanoparticles suitable for highly sensitive monitoring of local magnetic field fluctuations and paramagnetic species under physiological conditions.