Detecting an Itinerant Optical Photon Twice without Destroying It

Nondestructive quantum measurements are central for quantum physics applications ranging from quantum sensing to quantum computing and quantum communication. Employing the toolbox of cavity quantum electrodynamics, we here concatenate two identical nondestructive photon detectors to repeatedly detect and track a single photon propagating through a 60 m long optical fiber. By demonstrating that the combined signal-to-noise ratio of the two detectors surpasses each single one by about 2 orders of magnitude, we experimentally verify a key practical benefit of cascaded nondemolition detectors compared to conventional absorbing devices.

Automated summary

Nondestructive quantum measurements are crucial for a wide range of quantum physics applications, and by connecting two identical nondestructive photon detectors and demonstrating a significant increase in signal-to-noise ratio, the practical benefits of cascaded nondemolition detectors have been experimentally verified.