Detection of Electron Paramagnetic Resonance of Two Electron Spins Using a Single NV Center in Diamond

A nitrogen-vacancy (NV) center is a promising quantum sensor, enabling measurement of an extremely small magnetic field, magnetic resonance spectroscopy with single spin sensitivity, and quantum simulations. A system with interacting spins is a great platform for fundamental physics and applications in quantum information science. For example, short-range and disordered spin interactions can give rise to novel quantum phases like quantum spin liquid and discrete time crystalline (DTC) and generate entanglement or spin squeezing to realize enhanced sensitivity beyond the standard quantum limit. NV-detected electron paramagnetic resonance (NV-EPR) spectroscopy with a single NV center is a powerful method to study nanoscale environments of interacting electron spins. However, only a few demonstrations have been performed to determine the number of interacting electron spins and individual coupling strength to the NV center. In this presentation, we discuss the demonstration of NV-EPR spectroscopy of two electron spins. We employ a single shallow NV center in diamond as a sensor and utilize a double electron-electron resonance (DEER) technique and dynamical decoupling sequence (CPMG-8) to show the detection of EPR signals of surrounding spins. Moreover, we present a simple model to determine the number of the detected spins and the strengths of their magnetic dipole interactions. The presented spin system will be useful for investigating quantum effects that require a low number of spins or realizing entangled quantum sensing.