Observation of cross phase modulation in cold atom gradient echo memory

Strong nonlinear interactions between single photons have important applications in optical quantum information processing. Demonstrations of these interactions in cold atomic ensembles have largely been limited to exploiting slow light generated using electromagnetically induced transparency (EIT). However, these EIT implementations have limited achievable phase shifts due to spontaneous emission. Here, we demonstrate and characterize a scheme free from these limitations using gradient echo memory with inferred single photon phase shifts of 0.07 +/- 0.02 mu rad. Excellent agreement with theoretical modelling was observed. Degradation of memory efficiency was observed for large phase shifts but strategies to overcome that are presented.

Automated summary

Researchers propose a scheme based on gradient echo memory to achieve strong nonlinear interactions between single photons in cold atomic ensembles, overcoming the limitations caused by spontaneous emission. The effectiveness of the scheme is experimentally demonstrated, and strategies to address the degradation of memory efficiency caused by large phase shifts are presented.