Simultaneous Wide-field Imaging of Phase and Magnitude of AC Magnetic Signal Using Diamond Quantum Magnetometry

Spectroscopic analysis of AC magnetic signal using diamond quantum magnetometry is a promising technique for inductive imaging. Conventional dynamic decoupling like XY8 provides a high sensitivity of an oscillating magnetic signal with intricate dependence on magnitude and phase, complicating high throughput detection of each parameter. In this study, a simple measurement scheme for independent and simultaneous detection of magnitude and phase is demonstrated by a sequential measurement protocol. Wide-field imaging experiment was performed for an oscillating magnetic field with approximately 100$\mu$m-squared observation area. Single pixel phase precision was $2.1^\circ$ for 0.76$\mu$T AC magnetic signal. Our method enables potential applications including inductive inspection and impedance imaging.Comment: 9 pages, 4 figure

Fast coherent control of nitrogen-14 spins associated with nitrogen-vacancy centers in diamonds using dynamical decoupling

A nitrogen-vacancy (NV) center in a diamond enables the access to an electron spin, which is expected to present highly sensitive quantum sensors. Although exploiting a nitrogen nuclear spin improves the sensitivity, manipulating it using a resonant pulse requires a long gate time owing to its small gyromagnetic ratio. Another technique to control nuclear spins is a conditional rotation gate based on dynamical decoupling, which is faster but unavailable for nitrogen spins owing to the lack of transverse hyperfine coupling with the electron spin. In this study, we generated effective transverse coupling by applying a weak off-axis magnetic field. An effective coupling depends on the off-axis field; the conditional rotation gate on the nitrogen-14 spins of an NV center was demonstrated within 4.2 {\mu}s under an 1.8% off-axis field and a longitudinal field of approximately 280 mT. We estimated that a population transfer from the electron to nitrogen spins can be implemented with 8.7 {\mu}s. Our method is applicable to an ensemble of NV centers, in addition to a single NV center

Wide-field quantitative magnetic imaging of superconducting vortices using perfectly aligned quantum sensors

Various techniques have been applied to visualize superconducting vortices, providing clues to their electromagnetic response. Here, we present a wide-field, quantitative imaging of the stray field of the vortices in a superconducting thin film using perfectly aligned diamond quantum sensors. Our analysis, which mitigates the influence of the sensor inhomogeneities, visualizes the magnetic flux of single vortices in YBa$_2$Cu$_3$O$_{7-\delta}$ with an accuracy of $\pm10~\%$. The obtained vortex shape is consistent with the theoretical model, and penetration depth and its temperature dependence agree with previous studies, proving our technique's accuracy and broad applicability. This wide-field imaging, which in principle works even under extreme conditions, allows the characterization of various superconductors