  Single spin detection is one of the important tasks in the field of quantum
metrology. Many experiments about the single spin detection has been performed.
However, due to the weak magnetic fields from the single spin, a long
measurement time is required to achieve a reasonably high signal-to-noise
ratio. Here, we propose an alternative way to realize rapid and accurate single
spin detection with entangled states. While it is known that entanglement can
improve the sensitivity to measure globally applied magnetic fields, we
investigate a strategy to use the entanglement for detecting spatially
inhomogeneous magnetic fields from the target single spin. We show that the
entanglement significantly increases the signal to noise ratio for the single
spin detection even under the effect of realistic noise. Our results pave the
way for practical single spin detection.
