Fig. 5. GHZ-state tomography.

a Fidelity of each GHZ state, with error bars showing the standard error. b The experimental density matrix of the first GHZ state, $∣{\mathrm{\Phi }}^{+}⟩$, in good agreement with the theoretical matrix (inset). This agreement is achieved by a new tomography based on visibility at specific z planes for each polarisation projection, illustrated in c for one projection, showing the interference pattern at the overlapping region of the two orbits corresponding to the GHZ state. Experimental (Exp.) and theoretical (Sim.) results are shown for the states of d $∣{\mathrm{\Phi }}^{\pm }⟩$, e $∣{\mathrm{\Psi }}_1^{\pm }⟩$, f $∣{\mathrm{\Psi }}_2^{\pm }⟩$ and g $∣{\mathrm{\Psi }}_3^{\pm }⟩$, and the illustration on the left for each panel shows the location of the CCD camera when capturing the interference fringes