Experimental test of nonlocal realism using a fiber-based source of polarization-entangled photon pairs

We describe an experimental test of local realistic and nonlocal realistic theories using polarization-entangled two-photon singlet states created using a fiber-based polarization Sagnac interferometer. We show a violation of Bell’s inequality in the Clauser-Horne-Shimony-Holt form by 15 standard deviations, thus excluding local hidden-variable theories, and a violation of a Leggett-type nonlocal hidden-variable inequality by more than three standard deviations, thus excluding a class of nonlocal hidden-variable theories.

Figure 1

(Color online) Top: Poincaré spheres showing the polarization analyzer settings in detecting the signal (left) and idler (right) photons. Bottom: Schematic of the experimental setup. Fiber: polarization-maintaining microstructure fiber, PBS: polarizing beam splitter, $\lambda ∕2$: half-wave plate, $\lambda ∕4$: quarter-wave plate, M: mirror, and IF: interference filter. The Sagnac interferometer outputs Bell states in the form of $H_{\text{signal}}{H}_{\text{idler}}-V_{\text{signal}}{V}_{\text{idler}}$, which are rotated to be the singlet state ${\Psi }^{-}=H_{\text{signal}}{V}_{\text{idler}}-V_{\text{signal}}{H}_{\text{idler}}$ by the first half-wave plate in the idler arm.

Figure 2

(Color online) Measured values (blue circles), the quantum prediction (red line), and the classical limit (black line) of $S_{\mathrm{NLHV}}$ [(a) and (c)] and $S_{\mathrm{CHSH}}$ [(b) and (d)] as a function of $\phi$ at two pairs of wavelengths: ${\lambda }_{\text{signal}}=689\mathrm{nm}$, ${\lambda }_{\text{idler}}=800\mathrm{nm}$ [(a) and (b)], and ${\lambda }_{\text{signal}}=685\mathrm{nm}$, ${\lambda }_{\text{idler}}=805\mathrm{nm}$ [(c) and (d)].