High radiation efficiency and tunable resonance planar double-turn spiral antenna for manipulation of nitrogen-vacancy centers.

Nitrogen-vacancy (NV) centers in diamond are promising quantum sensors, where microwave antennas play a crucial role in manipulating the spin states accurately. Conventional microwave antennas often struggle to balance radiation efficiency and bandwidth. To address this challenge, we design a planar double-turn spiral antenna (PDTSA), based on the ring microstrip antenna (RMA). PDTSA demonstrates an ∼4.5-fold increase in radiation efficiency compared to RMA. In addition, the PDTSA allows linear tunability of the resonance frequency up to 500 MHz by adjusting the spiral input length. This feature addresses the limitations of a narrow working frequency range, which are typically caused by the narrowband in high-radiation-efficiency antennas. The experimental results show that at an absolute input power of 1 W, the PDTSA increases the Rabi frequency from 1.72 to 8.06 MHz compared to the RMA. This enhancement accelerates quantum state manipulation and reduces phase accumulation errors. These characteristics make PDTSA suitable for applications in quantum sensing and precision measurements using NV centers. [ABSTRACT FROM AUTHOR]