Generation of ultrabright tunable polarization entanglement without spatial, spectral, or temporal constraints

Abstract

The need for spatial and spectral filtering in the generation of polarization entanglement is eliminated by combining two coherently driven type-II spontaneous parametric down-converters. The resulting ultrabright source emits photon pairs that are polarization entangled over the entire spatial cone and spectrum of emission. We detect a flux of $\sim \mathrm{12\hspace{0.17em}000}$ polarization-entangled pairs/s per mW of pump power at $90\%$ quantum-interference visibility, and the source can be temperature tuned for $5\text{nm}$ around frequency degeneracy. The output state is actively controlled by precisely adjusting the relative phase of the two coherent pumps.