Study of a single nitrogen-vacancy center in diamond to detect surrounding electron spins

A nitrogen-vacancy (NV) center in diamond is a promising candidate for applications of nanoscale magnetic sensing as well as for investigation of fundamental quantum sciences because of its unique properties including capability to detect a NV center, long decoherence time even at room temperature, stable fluorescence and biocompatibility. Here we will present our approach to use a single NV center in diamond to probe tiny magnetic fields ($\sim$ uT or less) due to surrounding spin environments. We will discuss magnetic field dependence of spin decoherence in a single NV center as well as use of double electron-electron resonance spectroscopy to detect surrounding electron spins.