Coherent manipulation of nuclear spins in the strong driving regime*

Spin-based quantum sensing and quantum computing rely on manipulating the spin state of the sample of interest or information qubits. Fast spin state manipulation is desirable to expedite experiments, to enhance sensitivity, and to enable application of elaborate pulse sequences with a limited coherence time. Strong driving using intense radio-frequency (RF) fields can thus facilitate fast manipulation and enable broadband excitation of spin species.

Here, we designed and implemented a spiral RF antenna capable of delivering intense fields to a sample. The planar antenna is tailored for quantum sensing experiments using the diamond's nitrogen vacancy (NV) center. We demonstrate the antenna by driving Rabi oscillations in $^1$H spins in an immersion oil sample on the diamond’s surface and measure Rabi frequencies higher than 500 kHz, corresponding to pi-pulses shorter than 1 $mu$s.

We discuss the implications of driving spins in a regime where the driving strength is comparable to the spin-state splitting, i.e., where the rotating wave is no longer a valid approximation. We present a simple recipe to optimize pulse fidelity in this regime, considering various driving field angles.