ZERO BIAS FIELD SELECTIVE TRANSITION ADRESSING OF THE NV CENTER VIA PULSE SHAPING

Nitrogen-vacancy (NV) centers in diamond are widely used for vector magnetometry, but standard techniques typically require an external bias magnetic field to distinguish between the four possible crystallographic orientations of the NV centers. This bias field is often problematic, as it can introduce measurement errors through thermal or mechanical drifts and interfere with the system being studied. The authors investigate whether it is possible to achieve orientation-selective and transition-selective control of NV ensembles at zero bias field using advanced pulse-shaping techniques.

To address the challenge of spectral overlap at zero bias, the authors develop a quantum optimal control framework. They model the NV ensemble using a block-diagonal representation in the fundamental irreducible representation of su(3), which allows for efficient simulation of large ensembles. They then use the Gradient Ascent Pulse Engineering (GRAPE) algorithm to design microwave pulses that selectively drive specific spin transitions for a chosen NV orientation. The framework incorporates robustness by optimizing pulses against random distributions of magnetic and electric field inhomogeneities, ensuring the control remains effective despite local variations in the diamond lattice.

The study demonstrates that selective spin manipulation is feasible without a bias field. By optimizing the microwave driving fields, the authors show that they can implement high-fidelity gates on specific NV orientations while keeping others in their ground state. Simulations indicate that these optimized pulses maintain high state-transfer fidelities (exceeding 99%) even when subjected to significant magnetic and electric field perturbations. The authors also identify an inverse relationship between pulse duration and control amplitude, providing a practical guide for balancing speed and experimental feasibility.