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Figure 5: If one records the which-way information by entangling the photon paths with another degree of freedom there will be no destructive interference of the branch vectors at path 4 and the which-way information claims from the two single-path setups can be applied to this mixed setup also. In such a scenario the photon density matrix is not that of a pure state but mixed one. Red and blue branch vectors denote either photons with orthogonal polarizations (such as | 𝑅 and | 𝐿 ) or photons propagating at different times ( 𝑡 1 and 𝑡 2 ), in either case destructive interference at arm 4 cannot occur.