I am a little bit confused about photon particle/wave duality. Do we have to interact with photon to detect it? Or without interacting photon, only by its wave nature, can we detect the existence of a photon. Consider the following image:
Can detector2 at a sufficient distance, detect the moving photon in a way?
Here is a link on manipulating individual quanta :
Serge Haroche and his colleagues have developed an experiment to study the quantum mechanics of microwave light trapped between two mirrors (a cavity)1. They show that the quantum of light — the photon — can be controlled at an astonishing l evel of precision, and have used this to bring the abstract ideas of quantum entanglement to life in the laboratory.
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Haroche's group measures the intensity of trapped light using a non-destructive method that probes the light using atoms flying through the trap. Each atom acts as a clock whose ticking rate depends on its energy level. As an atom flies through the cavity, its energies are shifted by the trapped light, and the total number of ticks of the clock changes accordingly, without any light being absorbed.
When a kind of excited atom called a Rydberg atom is used, the technique is sensitive enough to detect a single photon, and repeated measurements allow the same photon to be observed as it lives and eventually dies in the cavity
So the photon is detected in a sense due to changes in the boundary conditions for the solution of the atom leaving the cavity. Its presence changes the quantum mechanical solutions for the exiting atoms, without affecting the photon's four vector.
