In a perspective article of Nature Photonics, Yaron Silberberg and Jean-Pierre Wolf explore the recent possibilities offered by quantum spectroscopy for sensing. Quantum interference pathways using ultrashort shaped laser pulses and entangled photons are both considered for opening new applications such as label free protein identification and atmospheric trace gas detection”

Spooky spectroscopy. To measure the sample’s infrared absorption, a photon from the visible pump beam is split into a visible ‘signal’ photon and an infrared ‘idler’ photon by a nonlinear crystal. The infrared idler photon interacts with the sample. The two photons then cross a second crystal, where another photon pair can be generated. By measuring the visible signal photons (which never passed through the sample) one can detect the infrared properties of the sample.