Coherent manipulation of nuclear spins in the strong driving regime

Abstract

Spin-based quantum information processing makes extensive use of spin-state manipulation. 
This ranges from dynamical decoupling of nuclear spins in quantum sensing experiments to 
applying logical gates on qubits in a quantum processor. Fast manipulation of spin states 
is highly desirable for accelerating experiments, enhancing sensitivity, and applying 
elaborate pulse sequences. Strong driving using intense radio-frequency (RF) fields can, 
therefore, facilitate fast manipulation and enable broadband excitation of spin species. 
In this work, we present an antenna for strong driving in quantum sensing experiments and 
theoretically address challenges of the strong driving regime. First, we designed and 
implemented a micron-scale planar 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 and should be applicable to other solid-state defects. 
The antenna has a broad bandwidth of 22 MHz, is compatible with scanning probes, and is 
suitable for cryogenic and ultrahigh vacuum conditions. We measure the magnetic field induced 
by the antenna and estimate a field-to-current ratio of  G/A, representing a six-fold increase 
in efficiency compared to the state-of-the-art, crucial for cryogenic experiments. 
We demonstrate the antenna by driving Rabi oscillations in 1H spins of an organic sample 
on the diamond surface and measure 1H Rabi frequencies of over 500 kHz, i.e. -pulses shorter 
than 1 —an order of magnitude faster than previously reported in NV-based nuclear magnetic 
resonance (NMR). Finally, we discuss the implications of driving spins with a field tilted 
from the transverse plane in a regime where the driving amplitude is comparable to the 
spin-state splitting, such that the rotating wave approximation does not describe the 
dynamics well. We present a simple recipe to optimize pulse fidelity in this regime based 
on a phase and offset-shifted sine drive, which may be optimized in situ without numerical 
optimization procedures or precise modeling of the experiment. We consider this approach 
in a range of driving amplitudes and show that it is particularly efficient in the case of 
a tilted driving field. The results presented here constitute a foundation for implementing 
fast nuclear spin control in various systems.