At the nanoscale, isolated spins can be exceedingly stable and precisely controlled. Their natural stability also renders them sensitive magnetic, electric, and thermal probes. Recent experimental advances have enabled the control and manipulation of individual quantum mechanical spins – Nitrogen-Vacancy (NV) defects – in diamond.

In each defect, a nitrogen atom and an adjacent vacancy substitute for two carbon atoms in the diamond lattice. The NV has a spin triplet electronic ground state that can be polarized, manipulated and optically detected. Our group is interested in demonstrating the various dynamical processes at room temperature or low temperature with single and ensemble NV spins. These dynamics can be theoretically important or promote the quantum sensing techniques.

Spin Squeezing in NV System

One of the long-standing challenges within the solid-state quantum sensing community, is the demonstration and then use of many-body entanglement to perform enhanced sensing. In particular, for an ensemble of 𝘕 sensors, it is possible to identify entangled states that exhibit an enhanced sensitivity scaling better than 𝓞(𝟣∕√𝘕) which is often referred to as the standard quantum limit (SQL).

Among the known types of metrologically useful many-body entanglement, spin-squeezing stands out in the context of solid-state defect-based sensors. Previous demonstrations of spin-squeezing have essentially all been implemented in atomic systems, while recent theoretical work from our team has suggested short-range dipolar interactions can also lead to scalable spin squeezing beyond the SQL. So with thin layers of two-dimensional (111)-NV ensemble samples, we try to generate the spin-squeezing state in one of the ensemble NVs’ group and then probe the entanglement state by another NV group using noise spectroscopy.