The surprising persistence of time-dependent quantum entanglement

Abstract

The tension between simple and elegant theoretical models and the detailed experimental reality is particularly pronounced in interferometer-based entanglement quantum imaging (IEQI). Experimental systems contain pump beams that start in impure states and that are depleted, quantum noise that affects -and drives -any otherwise gradual build up of the signal and idler fields, and nonlinear materials that are far from ideal and have a complicated time-dependent dispersive response. In particular, since group velocity mismatches change the relative timings of induced signal-idler entanglements, we would normally expect this to generate "which path" information that destroys any possibility of measurable IEQI. Here we show how the time-domain entanglement crucial for quantum interferometry can be -and is -recoverable despite the obscuring effects of real-world experimental complications.