  Nitrogen vacancy (NV) centers in diamond are promising systems for realizing
sensitive temperature sensors. Pulsed optically detected magnetic resonance
(Pulsed-ODMR) is one of the ways to measure the temperature using NV centers.
However, Pulsed-ODMR requires careful calibration and strict time
synchronization to control the microwave pulse, which complicates its
applicability. Nonetheless, the continuous-wave optically detected magnetic
resonance (CW- ODMR) in NV centers is another more advantageous way to measure
temperature with NV centers, owing to its simple implementation by applying a
green laser and microwave in a continuous manner. This, however, has the
drawback of a lower sensitivity compared to pulsed-ODMR. Therefore, to benefit
from its accessible adaptation, it is highly important to improve the
sensitivity of temperature sensing with CW-ODMR. Here, we propose a novel
method to measure temperature using CW-ODMR with a quantum state dressed by
radio-frequency (RF) fields under transverse magnetic fields. RF fields are
expected to suppress inhomogeneous broadening owing to strain variations.
Experimental results confirmed that the linewidth becomes narrower in our
scheme compared to the conventional one. Moreover, we estimated the sensitivity
to be approximately 65.5 $\mathrm{m}\mathrm{K}/\sqrt{\mathrm{Hz}}$, which
constitutes approximately seven times improvement with respect to the
sensitivity of the conventional scheme.
