Distilling strong entanglement from a weakly entangled source

Monday 18 Mar 13
We published our recent theoretical results on displacement-enhanced entanglement distillation in Optics Express.

Entanglement distillation is the process of consuming multiple weakly entangled quantum states (possibly degraded through distribution losses) in order to obtain fewer, more highly entangled states. It has been known for a while that photon subtraction is a powerful method for distillation of a two-mode squeezed state. We show that - somewhat counter-intuitively - it is possible to obtain even higher entanglement by distilling an initial single-mode squeezed vacuum state, as long as the photon subtraction-based distillation process is preceded by a simple displacement operation.


20130318 opex displacement distillation setup.jpg   20130318 opex displacement distillation entanglement.jpg'


In the graph above, the solid black curve shows the amount of entanglement that can be obtained from the pre-distillation entanglement (dotted black curve) by implementing a displacement-enhanced photon subtraction on both modes as in the sketch on the left. In the low-squeezing regime (left-hand side of the graph), the attainable entanglement when the initial source is a single-mode squeezer considerably outperforms that of an initial two-mode squeezer (yellow solid curve), which is otherwise experimentally harder to implement.


In the paper, we also investigate in detail the influence of losses, non-optimal displacement amplitudes and non-ideal photon detectors. The results, which are based on Anders' PhD thesis material, were published in the paper "Displacement-enhanced entanglement distillation of single-mode-squeezed entangled states" in Optics Express.