We propose a photon-arrival detector (PAD), which detects the arrival of a signal photon and simultaneously projects the signal input state to a single photon state, with an atom-cavity system. In this proposal, use of a V-type system as the intracavity atom is discussed for implementing the PAD, since V-type systems have been widely studied in the field of solid state, enabling us to miniaturize and integrate that implementation. The performance of the proposed PAD is evaluated for a specific

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... ethod of the detection process. The proposed PAD is capable of repeating the procedure for detecting the arrival of input photons and it has improves the detection probability so that it has a higher quantum efficiency than those of conventional photodetectors.