Figure 2

The diagram of experimental setup. The experiment consists of two stages, the state preparation stage and the measurement stage. GL: Glan lens. HWP(i): half wave plate (i = 1, …, 6). PBS(i): polarizing beam splitter (i = 1, …, 5). PD(i): photoelectric detector (i = 1, …, 3). The angles of HWP3 and 4 are set as 0° for path-length compensation.