Experimental generation of polarization entanglement from spontaneous parametric down-conversion pumped by spatiotemporally highly incoherent light

We investigate the cross influence of the pump coherence on the entanglement produced from spontaneous parametric down-conversion (SPDC) in different degrees of freedom (DOFs). We experimentally demonstrate the generation of polarization entanglement from SPDC pumped by a spatiotemporally highly incoherent (STHI) light-emitting diode. Our quantum state tomography measurements using multimode collection fibers to avoid postselection yield a two-qubit state with the concurrence of 0.531 +/- 0.006 and purity of 0.647 +/- 0.005, in excellent agreement with our theoretically predicted concurrence of 0.552 and purity of 0.652. We find that using an STHI pump reduces the entanglement and purity of the output polarization two-qubit state due to a coupling between the spatiotemporal and polarization DOFs introduced by the birefringence and dispersion of the nonlinear crystal. The viability of SPDC with STHI pumps is important for two reasons: (i) STHI sources are ubiquitous and available at a wider range of wavelengths than lasers, and (ii) the generated STHI polarizationentangled two-photon states could potentially be useful in long-distance quantum communication schemes due to their robustness to scattering.

Automated summary

We investigated the impact of pump coherence on entanglement produced from SPDC in different DOFs. By using a STHI light-emitting diode as the pump, we achieved the generation of polarization entanglement. The measured two-qubit state had a concurrence of 0.531+/-0.006 and a purity of 0.647+/-0.005, which matched well with the predicted values. We found that using a STHI pump reduced the entanglement and purity of the output polarization two-qubit state due to the coupling between spatiotemporal and polarization DOFs.