Two-level systems are at the core of numerous real-world technologies such as magnetic resonance imaging and atomic clocks. Coherent control of the state is achieved with an oscillating field that drives dynamics at a rate determined by its amplitude. As the strength of the field is increased, a different regime emerges where linear scaling of the manipulation rate breaks down and complex dynamics are expected. Employing a single spin as a canonical two-level system, we have measured the room-temperature "strong-driving" dynamics of a single nitrogen vacancy center in diamond. Using an adiabatic passage to calibrate the spin rotation, we observe dynamics on subnanosecond time scales. Contrary to conventional thinking, this breakdown of the rotating wave approximation provides opportunities for time-optimal quantum control of a single spin.
13 pages of supplemental material