Photon detectors typically function by absorbing photons, which triggers a cascade effect resulting in measurable current flow, based on the photoelectric effect. The discussion raises the question of whether photon detectors can detect photons without absorption, allowing for further testing. It is noted that the act of detection alters both the detector and the photon, suggesting limitations in traditional detection methods. The concept of "weak measurement" and quantum non-demolition measurement is introduced as potential avenues for detecting photons without destruction. Further exploration of these advanced measurement techniques could provide insights into non-invasive photon detection.
