A single spin is the smallest possible magnetic field sensor, with quantum-limited sensitivity and nanoscale spatial resolution. Electronic spins associated to spin-active point defects such as the nitrogen-vacancy (NV) colour centre in diamond are widely used as nanoscale quantum sensors in a variety of geometries (scanning probe microscopes, widefield sensing, etc) over a wide temperature range. Our work in this area is related to the optimisation of the sensor capabilities, in particular with nanoscale magnetic resonance in mind, and to its application to study many-body physics and magnetic ordering in 2D materials.

Real-time adaptive optimisation and machine learning. One of the main bottlenecks for NV magnetometry is the data acquisition time: especially for long dynamical decoupling sequences with high spectral selectivity, required in nanoscale magnetic resonance, the signal acquisition timescales become prohibitively long. Our solution is to add self-optimisation capabilities to our sensor, developing Bayesian algorithms that enable optimising measurement settings in real-time based on previous outcomes. The settings are updated using simple heuristics or, in more complex multi-parameter cases, by policies developed through model-aware reinforcement learning. We implement these type of protocols using real-time microcontrollers, FPGAs and programmable arbitrary waveform generators (see MJ Arshad et al, Physical Review Applied (2024) for a description of our adaptive quantum sensing setup).
In addition, we are developing automated learning algorithms to extract information from the environment. This is particularly important in nanoscale magnetic resonance, where the single-electron sensor detects simultaneously signals from multiple individual nuclear spins that need to be isolated and identified. This research is carried out in collaboration with the groups of Erik Gauger (quantum theory) and Yoann Altmann (applied statistics).

Quantum sensing of complex quantum materials. We have recently set-up a Nanoscale Quantum Sensing facility, including the first commercial scanning spin-based quantum sensor operating between 1.8-300K. Our goal is to use single spins to investigate magnetic fields and currents associated with quantum materials, in particular twisted 2D heterostructures.

Quantum sensing in bio-chemistry. We are very interested in applying spin-based quantum sensing to study interesting processes in surface chemistry and biology. If interested, you can for example read the Roadmap on Nanoscale Magnetic Resonance Imaging we co-authored with other leading international groups in this exciting field. Stay tuned for more information about this work!

For more information about his work, please contact Prof Cristian Bonato