Slowing the probe field in the second window of double-double electromagnetically induced transparency

TL;DR

This paper presents a method to control and slow down the probe field in the second transparency window of double-double EIT media, analyzing how physical parameters affect group velocity and transparency.

Contribution

The study introduces a scheme to reduce probe-field group velocity in the second EIT window, with analytical solutions and identification of three signal-field regimes for slowing light.

Findings

Group velocities can be lowered by parameter tuning.

Three regimes identified based on signal-field strength.

Second window's properties are sensitive to temperature-controlled nonlinearity.

Abstract

For Doppler-broadened media operating under double-double electromagnetically induced transparency (EIT) conditions, we devise a scheme to control and reduce the probe-field group velocity at the center of the second transparency window. We derive numerical and approximate analytical solutions for the width of EIT windows and for the group velocities of the probe field at the two distinct transparency windows, and we show that the group velocities of the probe field can be lowered by judiciously choosing the physical parameters of the system. Our modeling enables us to identify three signal-field strength regimes (with a signal-field strength always higher than the probe-field strength), quantified by the Rabi frequency, for slowing the probe field. These three regimes correspond to a weak signal field, with the probe-field group velocity and transparency window width both smaller for the second window compared to the first window, a medium-strength signal field, with a probe-field group velocity smaller in the second window than in the first window but with larger transparency-window width for the second window, and the strong signal field, with both group velocity and transparency window width larger for the second window. Our scheme exploits the fact that the second transparency window is sensitive to a temperature-controlled signal-field nonlinearity, whereas the first transparency window is insensitive to this nonlinearity.