Squeezing and entanglement delay using slow light

We examine the interaction of a weak probe with $N$ atoms in a $\Lambda$-level configuration under the conditions of electromagnetically induced transparency (EIT). In contrast to previous works on EIT, we calculate the output state of the resultant slowly propagating light field while taking into account the effects of ground state dephasing and atomic noise for a more realistic model. In particular, we propose two experiments using slow light with a nonclassical probe field and show that two properties of the probe, entanglement and squeezing, characterizing the quantum state of the probe field, can be well-preserved throughout the passage.

Figure 1

$\Lambda$ level structure of the atoms.

Figure 2

Setup to measure whether entanglement of slowed light is preserved. $\widehat{X}$ and $\widehat{Y}$ are two entangled beams where $\widehat{X}$ passes through an EIT medium and is consequently delayed by time ${\tau }_d$ while $\widehat{Y}$ travels in vacuum. The angle $\theta$ and $\varphi$ denotes the specific quadrature to be interrogated.