Quantum Sensing
Wide-field Magnetic Imaging Using Quantum Defects
The nitrogen-vacancy (NV) center is a defect that has a unique property: under certain excitation conditions, the intensity of its emitted photoluminescence (PL) is dependent on its spin state, and thus its local magnetic environment. We exploit this property to perform 2D magnetic imaging employing a nanometer-scale thick sheet of NV centers at the surface of a diamond chip. We fabricate these chips in-house as well as work with our diamond growth collaborators at AIST and Keio University.
We use optically-detected magnetic resonance (ODMR) to detect DC magnetic fields. In ODMR, the NV center is optically excited with a laser field while a RF field is swept in frequency across the electron spin resonance. PL from the NV center is collected during this sweep and an intensity dip is observed on resonance. The resonant frequency of this dip Zeeman shifts as a function of external magnetic field. At every pixel in our magnetic imaging microscope (e.g. one pixel may be the red curve, one pixel may be the blue curve below), we can can take a PL intensity measurement at a set of applied bias frequencies. The resulting image is a spatial map of that magnetic field. Below, we show a map of the magnetic field produced by several ferromagnetic nanoparticles deposited on top of the sensor substrate.
Dynamic Magnetic Particle Imaging
We have developed a sensing platform to perform orientation imaging of single magnetic nanoparticles in collaboration with biophysicist Paul Wiggins. The ongoing work involves both sensor development, quantum control of NV ensembles as shown above, as well as dynamic imaging of biologically-integrated of magnetic nanoparticles as depicted below.
DNA Bend Stiffness Measurement
The wide-field sensing platform is also being applied in a magnetic-tweezer (MT) assay to study the bending rigidity of individual DNA molecules at the nucleosome-scale (150 base pair, bp).
A DNA molecule is attached to the diamond sensor at one end and to a ferromagnetic bead at the other, as shown in the figure to the right. An external field is used to bend the DNA molecule, and vector magnetometry of the bead field and applied field is performed simultaneously. The bead moment vector is fit for a range of applied fields. Deflections between the applied field and bead moment enable measurement of the torque exerted by DNA on the bead.
Funding for this project is provided by NSF. Past support for this project has been provided by the UW Royalty Research Fund and UW Molecular Engineering and Science Institute.
Quantum Sensing with Colloidal Quantum Dots
Semiconductor quantum dots have size tunable energy bands giving superior control over their optical properties. Here we study CdSe quantum dots in the context of quantum sensing in collaboration with the Gamelin group. Adding a manganese (Mn) defect into the host matrix provides coupling of the defect to the optical transitions which can be used to sense external magnetic fields.
Recent Publications
Zeeshawn Kazi, Isaac M. Shelby, Hideyuki Watanabe, Kohei M. Itoh, Vaithiyalingam Shutthanandan, Paul. A. Wiggins, and Kai-Mei C. Fu, Wide-field dynamic magnetic microscopy using double-double quantum driving of a diamond defect ensemble Phys. Rev. Applied 15, 054032 (2021)