Abstract

Photons are ideal systems for the encoding and transmission of quantum information. However, although they are easy to send and manipulate, the discrimination of photon states is often not a trivial task. The major source of difficulty is due to the fact that photons do not interact. If this were the case it would be easy to implement conditional dynamics and therefore - for example - C-NOT gates. On the other hand it is possible to process information with photons utilizing their indistinguishability in interference by means of optical linear device. The interest on the implementation of quantum measurement by means of linear optical device is basically due to their simple physical realization. It is therefore important to investigate how we can extend the capability of this devices using ancillary photons in independent auxiliary modes, what role auxiliary states play in measurement processes with linear optical devices and how they can contribute for realization of non trivial measurement. The problem we address here is a generalization of the one already studied in connection with the problem of distinguishing Bell [1] states and ’’non-local without entanglement” states [2]. In this work we have investigated the problem of discrimination of two orthogonal N photon states by means of linear optical elements, conditional transformations and auxiliary photons.

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