Entangled-state generation with an intrinsically pure single-photon source and a weak coherent source

We report on the experimental generation of an entangled state with a spectrally pure heralded single-photon state and a weak coherent state. Our source, which was as efficient as that reported in our previous report [Phys. Rev. A 83, 031805 (2011)], was much brighter than those reported in earlier experiments using similar configurations. This entanglement system is useful for quantum information protocols that require indistinguishable photons from independent sources.

Figure 1

Schematic model of the experiment. A pure heralded single photon (V polarization) from SPDC is combined with a photon (H polarization) from LO at the beam splitter (BS). Then their polarization states are analyzed by two polarizers (${\theta }_1$ and ${\theta }_2$). The second idler photon from the SPDC is used as a heralder. Finally, these photons are detected by three detectors (APD) and recorded by a threefold coincidence counter (CC).

Figure 2

The experimental setup. BSP = beam sampler, DM = dichroic mirror, SPF = short-wave pass filter, LPF = long-wave pass filter, PBS = polarizing beam splitter, SMF = single-mode fiber, FBS = fiber beam splitter, QWP = quarter wave plate, HWP = half wave plate, MMF = multimode fiber, Pol = polarizer, Attn = attenuator, APD = avalanche photodiodes, CC = coincidence counter.

Figure 3

Experimental result of threefold coincidence counts as a function of the optical path delay, with a visibility of $85.4\pm 0.3\%$ with no background subtraction.

Figure 4

Experimental result of threefold coincidence counts as a function of polarizer 1 (${\theta }_1$) and polarizer 2 (${\theta }_2$). The data have no background subtraction.

Figure 5

Real (left) and imaginary (right) parts of the reconstructed density matrix.