“…As a prelude to our analysis of a truly interacting many-body system, we briefly present an analysis of the same system on the level of a single particle in the system, interacting with a single particle in the detector. According to this (over)simplified picture, particles going simultaneously through the interacting arms 2 and 3 (see figure 1), gain an extra phase e ig [35,36], where γ takes values in the range 0, . p [ ] First, we consider the intra-MZI operators, defined in a two-state single particle space, m , ñ {| } with m = 1, 2 for the 'system' (an electron propagating in arm 1 or 2) and similarly m = 3, 4 for the 'detector'.…”