The studies of many-body dynamics of interacting spin ensembles, as well as quantum sensing in solid state systems, are often limited by the need for high spin concentrations, along with efficient decoupling of the spin ensemble from its environment. In particular, for an ensemble of nitrogenvacancy (NV) centers in diamond, high conversion efficiencies between nitrogen (P1) defects and NV centers are essential, while maintaining long coherence times of an NV ensemble. In this work, we study the effect of electron irradiation on the conversion efficiency and the coherence time of various types of diamond samples with different initial nitrogen concentrations. The samples were irradiated using a 200 keV transmission electron microscope (TEM). Our study reveals that the efficiency of NV creation strongly depends on the initial conversion efficiency as well as on the initial nitrogen concentration. The irradiation of the examined samples exhibits an order of magnitude improvement in the NV concentration (up to ∼ 10 11 NV/cm 2 ), without degradation in their coherence times of ∼ 180 µs. We address the potential of this technique toward the study of many-body physics of NV ensembles and the creation of non-classical spin states for quantum sensing. The study of quantum many-body spin physics in realistic solid-state platforms has been a long-standing goal in quantum and condensed-matter physics. In addition to the fundamental understanding of spin dynamics, such research could pave the way toward the demonstration of non-classical spin states, which will be useful for a variety of applications in quantum information and quantum sensing. One of the leading candidates for such studies is the negatively charged nitrogen-vacancy (NV) center in diamond, having unique spin and optical properties, which make it useful for various sensing applications [1][2][3][4][5][6][7][8][9], as well as a resource for quantum information processing and quantum simulation [10][11][12].The current state-of-the-art is limited by the requirement of obtaining high spin concentrations while maintaining long coherence times. The sensitivity of magnetic sensing grows as the square-root of the number of spins [1,3], thus enhanced NV concentrations could improve magnetometric sensitivities. Furthermore, enhanced NV concentrations could lead to strong NV-NV couplings, which together with long coherence times, achieved using a proper dynamical decoupling protocol [13], could pave the way toward the study of many-body dynamics in the NV-NV interaction-dominated regime [10][11][12]. However, nitrogen defects not associated with vacancies (P1 centers) create randomly fluctuating magnetic fields that cause decoherence of the quantum state of the NV ensemble [14,15]. As a result, in most cases it would be beneficial to increase the concentration of NV centers while keeping the nitrogen concentration constant, i.e. improve the N to NV conversion efficiency.A common technique for improving the conversion efficiency is the irradiation of the sample with elec...

Magnetization in rock samples is crucial for paleomagnetometry research, as it harbors valuable geological information on long term processes, such as tectonic movements and the formation of oceans and continents. Nevertheless, current techniques are limited in their ability to measure high spatial resolution and high-sensitivity quantitative vectorial magnetic signatures from individual minerals and micrometer scale samples. As a result, our understanding of bulk rock magnetization is limited, specifically for the case of multi-domain minerals. In this work we use a newly developed nitrogen-vacancy magnetic microscope, capable of quantitative vectorial magnetic imaging with optical resolution. We demonstrate direct imaging of the vectorial magnetic field of a single, multi-domain dendritic magnetite, as well as the measurement and calculation of the weak magnetic moments of an individual grain on the micron scale. These results pave the way for future applications in paleomagnetometry, and for the fundamental understanding of magnetization in multi-domain samples.When igneous rocks in Earth's crust are formed by cooling of hot magma they acquire thermoremanent magnetization (TRM) parallel and proportional to the ambient field at the time of cooling. TRM can remain stable for millions of years preserving valuable geological magnetic information on complex long term processes, such as plate tectonic movements and formations of oceans and continents [1]. Despite its importance, little is known on the details of how thermoremanent magnetic information is acquired and retained in rocks [2]. Paleomagnetism, the science of studying natural magnetic information, heavily relies on Néel theory [3] of single-domain (SD) minerals. Yet, the dimensions of rock-forming minerals typically exceed the sub-micrometric threshold size for SD. As such, TRM is mostly held by multi-domain (MD) particles rather than by SD. In the absence of a general analytical formulation for TRM in MD, there is a growing need for direct observations of natural MD magnetization. Particularly, vectorial imaging of magnetic fields generated by MD particles with sub-micron spatial resolution and micrometer scale sample-detector distance, along with high sensitivity (µT / √ Hz), is critical for understanding the mechanism controlling the geometry and size of MD arrangements, the total moment exerted by individual natural crystals, and the stability of MD magnetic information over geological times.There are a number of magnetic imaging techniques that have been used in paleomagnetic research in a complementary fashion: Kerr effect [4] , Magnetic Force Microscopy (MFM) [5], electron holography [6], and SQUID microscopy [7]. Recently, a newly developed method based on nitrogen-vacancy (NV) magnetic microscopy [8][9][10], has been demonstrated by [11,12] in the context of paleomagnetometry. NV magnetic microscopy enables direct measurements of the three components of the magnetic field vector at a constant height above the sample in a room temperature environ...

No abstract