Schematic diagram showing the principle of the direct concurrence measurement of the hybrid entangled state. It consists of three PCMs, which have been described in Section 2. The structure of both PCM1 and PCM2 are shown in Fig. 1. In each round of the PCM, we pick up the odd parity states. We perform a Hadamard operation on the photon in spatial modes a₁ and c₁ with the help of HWP^22.5°. HWP^22.5° is a half-wave plate oriented at 22.5°, whose function is | H ⟩ → ( | H ⟩ + | V ⟩ ) / 2 and | V ⟩ → ( | H ⟩ − | V ⟩ ) / 2 .