Quantum Zeno Effect in the Quantum Non-Demolition Detection of Itinerant Photons

Understand

We analyze the detection of itinerant photons using a quantum non-demolition (QND) measurement.

• We show that the backaction due to the continuous measurement imposes a limit on the detector efficiency in such a scheme.
• We illustrate this using a setup where signal photons have to enter a cavity in order to be detected dispersively.
• In this approach, the measurement signal is the phase shift imparted to an intense beam passing through a second cavity mode.