Looking with quantum light: Ideas and perspectives in quantum metrology.
Fragile things need special handling: assessing physical properties with minimal invasivity is crucial when operating on samples, such as biological material, which can be easily modified by the presence of light fields. On the other hand, in optical measurement reducing the illumination level is unavoidably associated to the loss of precision, due to the impact of the shot noise. In time-dependent cases, this cannot be mitigated by accumulating statistics, as the collection interval is limited. Resolving this conundrum -- loss of precision against reduction of unwanted effects -- demands for a radically new approach. Controlling light down to the single quantum level can help mitigating this trade-off between precision and invasivity. While quantum mechanics cannot prevent losing precision at low illumination, the fundamental bounds are less strict than what is permitted by using only classical means. In this contribution, we will discuss how this idea is developing into the technology of quantum sensing, and where the challenges stand in the path of demonstrating fully functional sensors.