The Kerr Nonlinearity in an N -Type Four-Level System via Spontaneously Generated Coherence

Abstract

The Kerr nonlinearity is investigated in an N -type four-level atomic system whose both supper levels are degenerated or nearly degenerate. It is found that the spontaneously generated coherence as a result of the degenerate levels can change the Kerr nonlinearity dramatically depending on the angle between two spontaneous channels. In addition, we discover that the probe field makes its own contribution to the nonlinearity in comparison to indifference in general three-level systems.