[Illustration by Sanaz Faryadras]
Light often plays a key role in sensing applications, from the 4-km-long interferometer arms of gravitational-wave observatories to micro- and nanoscale devices capable of detecting and analyzing single molecules. As engineers chase ever-more-sensitive applications, however, they will eventually require new tools that go beyond the fundamental limits of conventional approaches, such as monitoring spectral-resonance shifts in optical cavities. Where will the extra sensitivity come from?