Ning Wang
Magnetic nanoparticles have wide applications in various fields, e.g., magnetic recording in information science, magnetic resonance imaging, and magnetic therapy in bio-medicine. In this chapter, we will review recent applications of magnetic nanoparticles or magnetic complexes in the cutting-edge field of quantum sensing, especially in hybrid quantum sensing. Quantum sensing is a quantum technology for ultrasensitive detection, which is particularly useful for sensing weak signals at the nanoscale. The quantum systems that offer unprecedented sensitivity, resolution, and/or flexibility include superconducting qubits, defect centers in solids, atomic vapors, cold atoms, and so on. Usually, they have spin properties and possess excellent magnetic-field sensitivity; but they are insensitive to temperature, electric field, pressure, etc., and even immune to some bio-parameters (e.g., pH and glucose concentration). Recently, hybrid quantum sensing has offered new possibilities. By converting the insensitive or immune parameters into magnetic signals, the range of detectable parameters of quantum sensing can be broadened significantly. In this chapter, we first give a brief introduction to diamond quantum sensing, then review the applications of magnetic nanoparticles or magnetic complexes in diamond quantum sensing and nano-magnetism, and finally, discuss the potential applications and challenges for hybrid diamond quantum sensing.