Generation of high-flux hyperentangled photon pairs using a microstructure-fiber Sagnac interferometer

We demonstrate generation of hyperentangled (time-bin and polarization) photon pairs via four-wave mixing in a microstructure-fiber Sagnac interferometer. The two-photon interference visibility in the time-bin (polarization) degree of freedom is $88\%\pm 2\%$ $(84\%\pm 1\%)$ without subtraction of accidental coincidences, and Bell’s inequality is violated by 27 standard deviations at a $1\mathrm{kHz}$ coincidence rate.

Figure 1

(Color online) A schematic of the experimental setup. BS, beam splitter; PBS, polarization beam splitter; MF, microstructure fiber; $\lambda ∕2$, half-wave plate; $\lambda ∕4$, quarter-wave plate; IF, interference filter; PA, polarization analyzer; (P)MI, (polarization) Michelson interferometer.

Figure 2

(Color online) A schematic of the time-bin analyzers, which transform the two time bins of the original hyperentangled state $(\mid \Psi {⟩}_{\mathrm{hyper}})$ into three time bins ($\mid 0{⟩}_{\mathrm{a}}$, $\mid 1{⟩}_{\mathrm{a}}$, and $\mid 2{⟩}_{\mathrm{a}}$), with the central time bin $(\mid 1{⟩}_{\mathrm{a}})$ containing the overlapped FWM amplitudes. $\lambda ∕4$, quarter-wave plate; PBS, polarization beam splitter; PMI, polarization Michelson interferometer.

Figure 3

(Color online) (a) Total coincidence rate $C_{\mathrm{total}}$ plotted as a function of the relative phase $\varphi$. (b) Time-bin TPI raw visibility $\approx 88\%$. (c) Total coincidence rate $C_{\mathrm{total}}$, coincidence rates $C_{\mathrm{V}0}$ and $C_{\mathrm{H}2}$, and accidental coincidence rate $A$ plotted against the half-wave plate angle in the polarization analyzer in the signal’s path. (d) Polarization TPI raw visibility $\approx 84\%$. Data are represented by solid dots, diamonds, squares, and triangles. The curves in (b) and (d) are sinusoidal fits to the TPI. $V$, visibility; TPI, two-photon interference.