Microwave Device Characterization Using a Widefield Diamond Microscope

Abstract

Devices relying on microwave circuitry form a cornerstone of many classical and emerging quantum technologies. A capability to provide in-situ, noninvasive and direct imaging of the microwave fields above such devices would be a powerful tool for their function and failure analysis. In this work, we build on recent achievements in magnetometry using ensembles of nitrogen vacancy centers in diamond, to present a widefield microwave microscope with few-micron resolution over a millimeterscale field of view, 130 nT Hz −1/2 microwave amplitude sensitivity, a dynamic range of 48 dB, and sub-ms temporal resolution. We use our microscope to image the microwave field a few microns above a range of microwave circuitry components, and to characterize a novel atom chip design. Our results open the way to high-throughput characterization and debugging of complex, multicomponent microwave devices, including real-time exploration of device operation.Microwave (MW) devices play a critical role in telecommunications, defence, and quantum technologies. Device characterization via high resolution MW field imaging is a long-standing goal [1][2][3], which promises to overcome the limitations of conventional characterization techniques. For example, it is difficult to identify internal features of complex devices using S-parameter measurements of reflection and transmission through external device ports [4,5]. A high-throughput MW imaging method would allow for fast prototype iteration, and for more adventurous development of novel device architectures. Furthermore, MW imaging is of interest for spin-wave imaging in magnonic systems [6,7], is under investigation for medical imaging [8,9], and can be used to characterize materials [10] and biological samples [11]. In recent years, alkali vapor cells with atoms in the ground [12][13][14][15][16] or highly excited Rydberg [17][18][19] states, and nitrogen-vacancy (NV) centers in diamond [20-23] have shown promise for intrinsically calibrated MW imaging in simple, vacuum-and cryogen-free environments. Ensembles of NVs in a widefield diamond microscope [24][25][26][27][28] provide an excellent balance between the sensitivity and wide field of view (FOV) offered by vapor cells and the nanoscale spatial resolution of single NV centers [29], and so far have been primarily employed for imaging static and low-frequency magnetic fields. In this work, we demonstrate high-throughput widefield diamond microscopy for MW device characterization, enabled by a step-change we have achieved in microscope performance.Our microscope integrates advances in camera speed, experiment control, novel diamond material, laser illu-

Wide-Field Imaging of Superconductor Vortices with Electron Spins in Diamond

“…In this work ensembles of NV centers in diamond are used for an alternative approach of imaging vortices. Utilizing ensembles has the important advantage of not requiring a physical scan of the sample (or the sensor), thereby opening the door for fast imaging up to video frame rates [15]. Here, we use this technique in a wideeld microscope to image vortices in an y rium barium copper oxide (YBCO) thin lm.…”

Determination of intrinsic effective fields and microwave polarizations by high-resolution spectroscopy of single nitrogen-vacancy center spins

“…Examples for these include nanoscale magnetic imaging of magnetically sensitive samples [32], or NV-based low-field techniques like zero and ultra-low field NMR [33]. The novel MW polarization analysis we demonstrated could find applications in NV-based MW imaging [34,35], which until now was only demonstrated for sensing of circularly polarized MWs [36]. Our results extend these capabilities and the existing toolset of NV-based quantum sensing modalities and would in principle allow for determining the full polarization state of MW fields with nanoscale resolutions, which has relevance in MW electronics [37] or spintronics devices [38].…”

Principles and techniques of the quantum diamond microscope

“…The laser polarization is easier to control, but focusing the laser at the objective back aperture can lead to burns. Techniques to avoid illuminating the sample as well as the NVs include illumination via total internal reflection in the diamond, shaping the pump laser beam into a light sheet using cylindrical lenses, or coating the NV surface with a reflective layer to reduce the optical intensity through the diamond chip [11,51,63]. Optimal photon collection efficiency requires the largest achievable numerical aperture (NA) for the microscope objective.…”

“…QDM imaging of the microwave field from wires, resonators, and structures is possible by measuring the Rabi frequency in a pulsed experiment [63], or by using the fluorescence contrast in a CW ODMR experiment [62] (see Figure 17A and 17B). An initial step is to compare the NV measurement to a predicted magnetic field map from a finite element method (FEM) calculation.…”