Energy-Time Entanglement Preservation in Plasmon-Assisted Light Transmission

We report on experimental evidence of the preservation of the energy-time entanglement of a pair of photons after a photon-plasmon-photon conversion. This preservation is observed in two different plasmon conversion experiments, namely, extraordinary optical transmission through subwavelength metallic hole arrays and long range surface plasmon propagation in metallic waveguides. Plasmons are shown to coherently exist at two different times separated by much more than their lifetimes. This kind of entanglement involving light and matter is expected to be useful for future processing and storing of quantum information.

Figure 1

Schematic of the experimental setup. One hole array is inserted at a time either in the 810 nm or in the 1550 nm designated U-bench. NL, nonlinear crystal; DM, dichroic mirror; PC, polarization controller; TAC, time to analog converter; APD, avalanche photodiode; $a$, lattice periodicity; $d$, hole diameters (see text).

Figure 2

Transmittance spectra of some hole arrays designed for transmission at 1550 nm (spectra of the samples designed for 810 nm have similar shapes). They shows mainly the dependencies of the peaks width with the hole diameters. Peaks’ heights are normalized by factors shown in between brackets in the legend. The small fast oscillations correspond to Fabry-Perrot effects at the glass substrate interfaces.

Figure 3

Schematic of the fiber U-bench used to excite LR-SP propagation through gold stripe waveguide. BCB, benzocyclobutene.

Figure 4

Interference fringes recorded for the three experiments. $V_{\mathrm{p}}$, net visibility of the shown fringes (with plasmonic conversion); $V_{\mathrm{ref}}$, reference net visibility (without plasmonic conversion); $T$, transmittance of the plasmonic device. The dashed horizontal line is the noise level (see text for details).