Continuous protection of a quantum state from inhomogeneous dephasing

Room-temperature atomic vapors are known for their simplicity and their potential scaling-up in applications. In spite of these benefits, laser-cooled atoms have evolved to be the prevalent systems for studying strong and coherent light-matter interactions, as the latter are unhindered by Doppler broadening. Here we present several methods to overcome the effective decrease of both atom-photon cross-section [1] and coherence time in vapors, and in fact in any inhomogeneously broadened atom-like system. The mechanism we study can be understood as the counteraction of the inhomogeneous dephasing of two coupled states, where one state has enhanced sensitivity to the source of dephasing. A far-detuned dressing field admixes a fraction Ω²/△² of this "sensor" state into the "protected" state, yielding a velocity-insensitive state and line-narrowing in two-color trasnitions [2]. Finally, we apply this method to extend the lifetime of collective excitations stored in a thermal atomic vapor. This method is continuous, in contrast to pulsed echo-based techniques.
[1] Lahad O., Finkelstein R., Davidson O., Michel O., Poem E. & Firstenberg O. (2019). Phys. Rev. Lett. 123 173203
[2] Finkelstein R., Lahad O., Michel O., Davidson O., Poem E. & Firstenberg O. (2019). New J. Phys. 21 103024