Subnatural linewidth using electromagnetically induced transparency in Doppler-broadened vapor

TL;DR

This paper demonstrates achieving subnatural linewidths in room-temperature rubidium vapor using electromagnetically induced transparency, overcoming Doppler broadening effects to observe linewidths as narrow as one-seventh of the natural linewidth.

Contribution

The study shows that Doppler-broadened vapor can exhibit subnatural linewidths through EIT, even with high control Rabi frequencies, which is a novel insight into vapor-based quantum coherence.

Findings

Linewidths as narrow as Γ/7 observed in Rb D2 line.

Subnatural linewidths maintained despite high control Rabi frequency.

Doppler effects can be mitigated in EIT to achieve narrow resonances.

Abstract

We obtain subnatural linewidth (i.e. $<\Gamma$) for probe absorption in room-temperature Rb vapor using electromagnetically induced transparency (EIT) in a $\Lambda$ system. For stationary atoms, the EIT dip for a resonant control laser is as wide as the control Rabi frequency $\Omega_c$. But in thermal vapor, the moving atoms fill the transparency band so that the final EIT dip remains subnatural even when $\Omega_c > \Gamma$. We observe linewidths as small as $\Gamma/7$ in the $D_2$ line of Rb.