Figure 1

Schematic diagram of experimental setup. A linearly polarized cw laser diode at 406 nm ($L$) pumps a couple of BBO crystals cut for type I down-conversion. The horizontal and vertical photon pairs are balanced by a half-wave plate set along the pump path, whereas an additional BBO crystal is set on the pump path to compensate for the temporal delay. Signal and idler cones travel through the SLM and are spatially selected by two irises and two slits set at $D=500$ mm with $\Delta x=5$ mm ($\Delta =10$ mrad). Two long-pass filters cut-on wavelength $715$ nm are used to reduce the background. A handmade grating can be inserted on the signal arm. Photons are focused in two multimode fibers (MMF’s) and sent to single-photon counting modules. Polarizers at the angles ${45}^{°}$, $-{45}^{°}$ or ${45}^{°}$, ${45}^{°}$ are inserted to measure visibility whereas a quarter-wave plate, a half-wave plate, and a polarizer are used for the tomographic reconstruction.Reuse & Permissions

Figure 2

Coincidence count distribution $C=|f_{\mathrm{expt}}(\theta ,{\theta }^{\text{'}}){|}^2$ for 10 s, within a coincidence time window of $50$ ns, as a function of the signal and idler slit positions $\theta$ and ${\theta }^{\text{'}}$. The phase-matching central angles correspond to $\theta ,{\theta }^{\text{'}}=0$.Reuse & Permissions

Figure 3

Visibility as a function of the evolution parameter $a$. Blue circles and red squares are the experimental data obtained with and without grating (errors within the symbols). The blue solid line and the red dashed line denote the corresponding theoretical predictions.Reuse & Permissions

Figure 4

Tomographic reconstruction of a state evolving in the effective non-Markovian channel. In the upper left plot the two-qubit density matrix just after the purification, with visibility $V=0.881\pm 0.004$. Upon increasing the evolution parameter to $a=0.23$ we achieve the minimum of entanglement oscillations: the density matrix is shown in the upper right plot, the corresponding visibility is $V=0.120\pm 0.016$. In the lower panels, we show the real and the imaginary parts of the reconstructed density matrix at the maximum of entanglement oscillations, which occurs for $a=0.48$. The corresponding visibility is $V=0.696\pm 0.013$, and the Bell parameter $B=2.341\pm 0.019$.Reuse & Permissions