A novel approach to quantum sensor control demonstrates experimentally verified improvements in sensitivity over other approaches when tasked to detect and characterize weak, time-varying magnetic fields in a noisy environment.
Quantum sensors take advantage of the inherent sensitivity of quantum systems to external environment perturbations to precisely measure target signals. The same interaction with the environment, however, limits the device sensitivity by reducing the coherence of the quantum states. Quantum control can play a crucial role in improving the sensor performance. We explore quantum control tools to improve the performance of a NitrogenVacancy (NV) center as a single-qubit sensor of ultra-weak magnetic fields in noisy environments. We present a method to obtain a precise spectroscopic characterization of the NV environment, instrumental to design robust sensing strategies with improved noise protection. Then, we exploit optimal quantum control based on a set of numerical methods to optimize the temporal dependence of the sensor driving field adapted to quantum sensing purposes, and prove its advantage to achieve best compromises between signal acquisition and noise cancellation.
The nitrogen-vacancy (NV) center in diamond is a quantum defect in diamond with unique properties for use in high-sensitive, high-resolution quantum sensors of magnetic fields. One of the most interesting and challenging application of NV quantum sensors is nanoscale magnetic resonance imaging (nano-MRI), which would enable to address single biomolecules. To this goal, improving the sensitivity of the NV sensor is a crucial task. Here, we present a quantum optimal control method that optimizes the sensitivity of NV sensor to specific weak magnetic signals with biologically-relevant, complex spectrum. The method, based on the mapping of the sensing problem on a problem of energy optimization of an Ising chain, allows us to improve sensitivity by three orders of magnitude compared to standard control sequences.