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Diamond based quantum sensing is a fast-emerging field with both scientific and technological importance. The nitrogen-vacancy (NV) center, a crystal defect in diamond, is a unique model system for microwave sensing application due to its excellent photo-stability, long spin coherence time in ambient conditions. In this work, we systematically optimized the measurement parameters for microwave sensing. The system noise is analyzed, and 1/f noise is suppressed by introducing a differential algorithm. The gain of avalanche photodiode and the gating window of the pulsed fluorescence is optimized to further suppress the noise floor. The decoherence of spin is characterized by varying the duration of the laser and microwave. The minimal detectable power on a standard microstrip is characterized with sampling time down to 1 ms, showing flat frequency dependence. The results have important implications toward fast measurement of broadband microwave power, especially in the field of IC testing and radar signal processing under intense electromagnetic interference.

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With the complexity and integration of integrated chips increasing, existing integrated circuits electromagnetic interference techniques using metallic probes cannot meet the emerging demand at single die level or wafer level, which requires micron spatial resolution and ultraweak invasiveness. In this article, we developed a non-invasive near field probe in the fiber format using nitrogen-vacancy center in diamond, which was attached to the tip of fiber as microwave B-field sensing element. Subsequently, we applied the fiber diamond probe to near field scanning of a low noise amplifier chip and a power amplifier chip. Through numerical simulation, we find that the surface field strength is proportional to current density at chip surface, thus this probe can be used as a current imaging technique at microwave frequency.