Weak-value amplification of light deflection by a dark atomic ensemble

Abstract

We study the coherent propagation of light whose dynamics is governed by the effective Schr\"odinger equation derived in a magneto-optically manipulated atomic ensemble with a four-level tripod configuration for electromagnetically induced transparency (EIT). The small transverse deflection of an optical beam, which is ultrasensitive to the EIT effect, could be drastically amplified via a weak measurement with an appropriate preselection and postselection of the polarization state. The physical mechanism is explained as the effect of wave-packet reshaping, which results in an enlarged group velocity in the transverse direction.