Real-time ghost imaging of Bell-nonlocal entanglement between a photon and a quantum memory

Quantum 5, 493 (2021).

https://doi.org/10.22331/q-2021-07-01-493

Certification of nonlocality of quantum mechanics is an important fundamental test that typically requires prolonged data collection and is only revealed in an in-depth analysis. These features are often particularly exposed in hybrid systems, such as interfaces between light and atomic ensembles. Certification of entanglement from images acquired with single-photon camera can mitigate this issue by exploiting multiplexed photon generation. Here we demonstrate this feature in a quantum memory (QM) operating in a real-time feedback mode. Through spatially-multimode spin-wave storage the QM enables operation of the real-time ghost imaging (GI) protocol. By properly preparing the spatial phase of light emitted by the atoms we enable observation of Bell-type nonlocality from a single image acquired in the far field as witnessed by the Bell parameter of $S=2.227pm0.007>2$. Our results are an important step towards fast and efficient utilization of multimode quantum memories both in protocols and in fundamental tests.