Figure 1

A NOON-state projection measurement for (a) four photons and (b) six photons. Q1, Q2, and Q3 are wave plates that introduce a relative phase shift of $\pi /2$, $2\pi /3$, and $4\pi /3$, respectively, between $H$ and $V$. $R$ is a rotator of 45°.Reuse & Permissions

Figure 2

Sketch of the experimental setup. IF: interference filter. PBS: polarization beam splitter.Reuse & Permissions

Figure 3

(a) Two-photon coincidences and (b) four-photon coincidences as a function of relative delay $c\Delta T$. The circles in (b) are the directly measured $ABCD$ coincidences, while the diamonds are the four-photon coincidences from Eq. (4) corresponding to the $2\times 2$ case. The solid curves are a Gaussian fit with a visibility of 90% and 33%, respectively.Reuse & Permissions

Figure 4

(a) Two-photon, (b) four-photon, and (c) six-photon coincidences as a function of relative delay $c\Delta T$. (ai) is for $AB$, (aii) for $AE$, and (aiii) for $BE$ in (a). (bi) is for $ABCE$, (bii) for $ABCD$, and (biii) for $BCDE$ in (b). The solid circles (ci) in (c) are the directly measured $ABCDEF$ coincidence, while the diamonds (ciii) are from two-photon data by Eqs. (4, 6) corresponding to the $2\times 3$ case, and the square points (cii) are from both two-photon and four-photon data by Eq. (6) corresponding to the $4\times 1+2$ case. The solid curves in (c) are a Gaussian fit with a visibility of 92%, 59%, and 39%, respectively. The data in (cii) and (ciii) are multiplied by 2 and 8, respectively, to bring them to a similar scale as (ci).Reuse & Permissions