Figure 1

(Color online) Projection measurement boxes. A series of PBSs and $22.5°$ rotated half wave plates (HWPs) construct all the six projection measurements. A 50:50 beam splitter (BS) followed by two single photon detectors acts as an equivalent photon resolved photon detector for detecting two photons heralded by twofold coincidence. Detectors $A$, $B$, $C$, and $D$ are all constructed by the setup shown in (j). (d) Projection of $P_{15}{P}_{16}$; (e) projection of $P_{24}{P}_{25}{P}_{26}$; (f) projection of $P_{34}{P}_{35}{P}_{36}$; (g) projection of $P_{24}{P}_{34}$; (h) projection of $P_{15}{P}_{25}{P}_{35}$; and (i) projection of $P_{16}{P}_{26}{P}_{36}$.Reuse & Permissions

Figure 2

(Color online) Decomposition of Fig. 1d. BS: beam splitter. (a) is for photon 1 and (b) is for photon 2. (c) and (d) show the setup of measurement $P_{15}$. They are the same except that the two photons are input in a different port. (e) and (f) show the setup of measurement $P_{16}$.Reuse & Permissions

Figure 3

(Color online) Experimental setup. The two-photon state generated from a spontaneous parametric down-conversion process is adjusted to $|H⟩\otimes |H⟩$. Two HWPs are used to reproduce the two-photon state to the product state $\left[\text{cos}\left(2{\theta }_1\right)|H⟩+\text{sin}\left(2{\theta }_1\right)|V⟩\right]\otimes \left[\text{cos}\left(2{\theta }_2\right)|H⟩+\text{sin}\left(2{\theta }_2\right)|V⟩\right]$, in which ${\theta }_1$ and ${\theta }_2$ are the rotation degrees of HWP1 and HWP2, respectively. IF: 3 nm bandwidth interference filter centered at 780 nm wavelength.Reuse & Permissions

Figure 4

(Color online) Experimental data against the arrival time difference between the two photons. The data are well fitted to Gaussian function. The inset shows the collinear Hong-Ou-Mandel (HOM) interference curve which determines the arrival time difference between the two photons.Reuse & Permissions

Figure 5

(Color online) Experimental data dependent on the input state.Reuse & Permissions