Observation of cross phase modulation in cold atom gradient echo memory

TL;DR

This paper demonstrates a novel scheme for observing cross phase modulation in cold atom gradient echo memory, achieving measurable single photon phase shifts without the limitations of EIT, with results aligning well with theory.

Contribution

The study introduces a new approach using gradient echo memory to observe cross phase modulation, overcoming previous limitations of EIT-based methods.

Findings

Inferred single photon phase shift of 0.07±0.02 μrad achieved.

Excellent agreement between experimental results and theoretical models.

Memory efficiency degrades at larger phase shifts, with strategies proposed to mitigate this.

Abstract

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 $0.07\pm0.02$ $\mu\text{rad}$. Excellent agreement with theoretical modelling was observed. Degradation of memory efficiency was observed for large phase shifts but strategies to overcome that are presented.