MICROwave quantum SENSing with diamond color centers (MICROSENS)

Detection and spectroscopy of weak microwave signals is of pivotal importance for key areas of modern technology, including wireless communication, radar, navigation and medical imaging. Solid-state spins could be attractive sensors for both tasks since they have transition frequencies that can be tuned across the 1-100 GHz range. However high-frequency sensing by solid state spins has remained underexplored so far, and most demonstrations of spin sensing have focused on low-frequency signals. The main reason is that well-established quantum sensing protocols suffer from a low efficiency in the high frequency domain. Furthermore, implementation of spin quantum sensors is not as mature compared to highly integrated microwave electronics. The purpose of the MICROSENS proposal is to use the well-known Nitrogen-Vacancy (NV) diamond colour centre as a tool to address these issues. We will build two different prototypes of microwave sensors based on the nitrogen- vacancy spin properties: a single microwave photon detector and a wideband quantum spectrum analyser. Theoretical aspects will also be jointly addressed by the MICROSENS project since understanding the ultimate limits of noise for high-frequency spin sensing will be one of the main objectives.

Detection and spectroscopy of weak microwave (>GHz) signals is of pivotal importance for key areas of modern technology, including wireless communication, radar, navigation and medical imaging. Solid-state spins could be attractive sensors for both tasks since they have transition frequencies that can be tuned across the 1-100 GHz range. However high-frequency sensing by solid state spins has remained widely under-explored so far, and most demonstrations of spin sensing have focused on low-frequency (<10MHz) signals. The main reason is that well-established quantum sensing protocols suffer from a low efficiency in the high frequency domain. Furthermore, implementation of spin quantum sensors is not as mature compared to highly integrated microwave electronics. The purpose of the MICROSENS proposal was to use the well-known Nitrogen-Vacancy (NV) diamond color center as a tool to address these issues. In the project at TU Wien we used a newly developed resonator design that allows coupling to a small ensemble of centers while still maintaining collectively strong coupling. This allows to use the ensemble of nitrogen-vacancy centers as a detector by harnessing superradiance as a detection mechanism. Signals as low as 40 photons at 3GHz can be detected, while still maintaining information about magnitude and phase of the signal measured. This results are an important step towards real world applications of large ensemble physics in the realm of quantum technology and will lead to new and important technological advancements.