Observation of EIT-enhanced cross-phase modulation in the short-pulse regime

TL;DR

This experiment demonstrates that electromagnetically-induced transparency (EIT) can enhance cross-phase modulation even with short laser pulses, maintaining a significant integrated phase shift crucial for quantum applications.

Contribution

It shows that narrow EIT windows continue to benefit cross-phase modulation with short pulses, contrary to prior assumptions, and the integrated phase shift scales inversely with EIT window width.

Findings

Peak phase shift saturates but does not drop in the short-pulse regime.

Time-integrated phase shift continues to scale inversely with EIT window width.

EIT-enhanced cross-phase modulation remains effective for short laser pulses.

Abstract

We present an experiment using a sample of laser-cooled Rb atoms to show that cross-phase modulation schemes continue to benefit from electromagnetically-induced transparency (EIT) even as the transparency window is made narrower than the signal bandwidth (i.e., for signal pulses much shorter than the response time of the EIT system). Addressing concerns that narrow EIT windows might not prove useful for such applications, we show that while the peak phase shift saturates in this regime, it does not drop, and the time-integrated effect continues to scale inversely with EIT window width. This integrated phase shift is an important figure of merit for tasks such as the detection of single-photon-induced cross phase shifts.