# Discerning quantum memories based on electromagnetically-induced-transparency and Autler-Townes-splitting protocols

## TL;DR

This paper distinguishes between EIT and ATS quantum memory protocols through numerical and experimental analysis, revealing their fundamental differences, optimal conditions, and regimes where they overlap, thus advancing quantum memory technology.

## Contribution

It provides a detailed comparison of EIT and ATS memory protocols, clarifying their differences, optimal conditions, and regimes of overlap through combined numerical and experimental studies.

## Key findings

- EIT relies on adiabatic elimination of absorption.
- ATS is based on absorption and non-adiabatic processes.
- Optimal memory conditions differ significantly for each protocol.

## Abstract

Electromagnetically induced transparency (EIT) and Autler-Townes splitting (ATS) are similar,but different quantum optical phenomena: EIT results from a Fano interference, whereas ATS is described by the AC-Stark effect. Likewise, despite their close resemblance, light-storage techniques based on the EIT memory protocol and the recently-proposed ATS memory protocol (E. Saglamyurek et al. Nature Photonics 12, 2018) are distinct: the EIT protocol relies on adiabatic elimination of absorption, whereas the ATS protocol is based on absorption. In this article, we elaborate on the distinction between EIT and ATS memory protocols through numerical analysis and experimental demonstrations in a cold rubidium ensemble. We find that their storage characteristics manifest opposite limits of the light-matter interaction due to their inherent adiabatic vs. non-adiabatic nature. Furthermore, we determine optimal memory conditions for each protocol and analyze ambiguous regimes in the case of broadband storage, where non-optimal memory implementations can possess characteristics of both EIT and ATS protocols. We anticipate that this investigation will lead to deeper understanding and improved technical development of quantum memories, while clarifying distinctions between the EIT and ATS protocols.