This monograph presents the emerging field of second-generation quantum sensing, which leverages phenomena such as superposition and entanglement, thereby offering measurement sensitivities far surpassing classical methods. In the discussion, the potential to revolutionize various scientific and technological domains is emphasized. Starting with a foundational overview of quantum sensors, distinguishing them from quantum computing and communication technologies, the relative maturity of quantum sensing is then highlighted, especially in room-temperature operations, which positions it closest to market adoption.The main part of the monograph is dedicated to solid-state defects, particularly nitrogen-vacancy (NV) centers in diamond, which have emerged as promising candidates for scalable quantum sensors. The unique optical and spin properties of NV centers are explored in detail, emphasizing their possible applications in fields such as biomedical imaging, materials science, and semiconductor inspection. The technical aspects of integrating NV centers with conventional electronic and photonic systems are delved into, discussing the challenges and innovations in electronic interface circuits photonic integration, and system-level integration technologies.Additionally, gas-based quantum sensors and examined, particularly those utilizing Rydberg atoms, which offer high precision due to their long coherence times. The challenges of integrating gas-based sensors, compared to their solid-state counterparts, are also briefly discussed. Overall, the monograph underscores the potential of second-generation quantum sensors, particularly those based on NV centers, to be the first scalable, high-volume quantum devices on the market, with applications spanning various fields due to their high sensitivity and room-temperature operation.
