Understanding Double Quantum Pulses with NV Centers

NV centers are important tools to perform quantum sensing of ac magnetic signals. The double quantum (DQ) protocol with NV centers, as opposed to single quantum (SQ), provides significant advantages such as twice the sensitivity to magnetic fields and insensitivity to strain and pressure effects. Therefore, understanding how the DQ state can be controlled and rotated during its precession is a crucial part of performing sophisticated ac sensing sequences. We will explain a nice DQ picture that is analogous to the SQ Bloch sphere, and how we have used it to understand initializations and rotations within the DQ state that can serve as a foundation for more complex pulse sequences where phasing is important.