Current comparator for both AC and DC ratio measurements with 10-8-level accuracy

Abstract: Accurate measurements of alternating current (AC) and direct current(DC) ratios are fundamental to electric power metrology. However, conventional current comparators for AC and DC typically rely on distinct technologies-electromagnetic induction for AC and superconducting quantum interference devices for DC. This technological divide leads to a fragmented and complex traceability system. Bridging this gap is critical for developing unified current standards that meet the demands of emerging power technologies. In this work, we present a compact, room-temperature AC/DC current comparator that integrates a diamond-based magnetometer using nitrogen-vacancy centers. The device achieves an accuracy of 10-8 for both AC and DC signals and supports a system bandwidth up to 300 Hz, without the need for cryogenics. It surpasses the performance of typical AC comparators, offering ten-fold higher accuracy, and matches that of state-of-the-art DC comparators. This unified, cryogenics-free solution not only enhances precision and versatility but also expands the applicability of the system to DC resistance bridges in quantum electrical standards.