GENIE[1] is a new neutrino event generator for the experimental neutrino physics community. The goal of the project is to develop a 'canonical' neutrino interaction physics Monte Carlo whose validity extends to all nuclear targets and neutrino flavors from MeV to PeV energy scales. Currently, emphasis is on the few-GeV energy range, the challenging boundary between the non-perturbative and perturbative regimes, which is relevant for the current and near future long-baseline precision neutrino experiments using accelerator-made beams. The design of the package addresses many challenges unique to neutrino simulations and supports the full life-cycle of simulation and generator-related analysis tasks.GENIE is a large-scale software system, consisting of ∼120,000 lines of C++ code, featuring a modern object-oriented design and extensively validated physics content.

Quantum spin dephasing is caused by inhomogeneous coupling to the environment, with resulting limits to the measurement time and precision of spin-based sensors. The effects of spin dephasing can be especially pernicious for dense ensembles of electronic spins in the solid-state, such as nitrogenvacancy (NV) color centers in diamond. We report the use of two complementary techniques, spin bath driving, and double quantum coherence magnetometry, to enhance the inhomogeneous spin dephasing time (T * 2 ) for NV ensembles by more than an order of magnitude. In combination, these quantum control techniques (i) eliminate the effects of the dominant NV spin ensemble dephasing mechanisms, including crystal strain gradients and dipolar interactions with paramagnetic bath spins, and (ii) increase the effective NV gyromagnetic ratio by a factor of two. Applied independently, spin bath driving and double quantum coherence magnetometry elucidate the sources of spin ensemble dephasing over a wide range of NV and bath spin concentrations. These results demonstrate the longest reported T * 2 in a solid-state electronic spin ensemble at room temperature, and outline a path towards NV-diamond DC magnetometers with broadband femtotesla sensitivity.

Remanent magnetization in geological samples may record the past intensity and direction of planetary magnetic fields. Traditionally, this magnetization is analyzed through measurements of the net magnetic moment of bulk millimeter to centimeter sized samples. However, geological samples are often mineralogically and texturally heterogeneous at submillimeter scales, with only a fraction of the ferromagnetic grains carrying the remanent magnetization of interest. Therefore, characterizing this magnetization in such cases requires a technique capable of imaging magnetic fields at fine spatial scales and with high sensitivity. To address this challenge, we developed a new instrument, based on nitrogen‐vacancy centers in diamond, which enables direct imaging of magnetic fields due to both remanent and induced magnetization, as well as optical imaging, of room‐temperature geological samples with spatial resolution approaching the optical diffraction limit. We describe the operating principles of this device, which we call the quantum diamond microscope (QDM), and report its optimized image‐area‐normalized magnetic field sensitivity (20 µT⋅µm/Hz1/2), spatial resolution (5 µm), and field of view (4 mm), as well as trade‐offs between these parameters. We also perform an absolute magnetic field calibration for the device in different modes of operation, including three‐axis (vector) and single‐axis (projective) magnetic field imaging. Finally, we use the QDM to obtain magnetic images of several terrestrial and meteoritic rock samples, demonstrating its ability to resolve spatially distinct populations of ferromagnetic carriers.

Electron spin resonance (ESR) describes a suite of techniques for characterizing electronic systems with applications in physics, chemistry, and biology. However, the requirement for large electron spin ensembles in conventional ESR techniques limits their spatial resolution. Here we present a method for measuring ESR spectra of nanoscale electronic environments by measuring the longitudinal relaxation time of a single-spin probe as it is systematically tuned into resonance with the target electronic system. As a proof of concept, we extracted the spectral distribution for the P1 electronic spin bath in diamond by using an ensemble of nitrogen-vacancy centres, and demonstrated excellent agreement with theoretical expectations. As the response of each nitrogen-vacancy spin in this experiment is dominated by a single P1 spin at a mean distance of 2.7 nm, the application of this technique to the single nitrogen-vacancy case will enable nanoscale ESR spectroscopy of atomic and molecular spin systems.