Enhanced Kerr nonlinearity via quantum interference from spontaneous emission

A novel atom configuration is proposed for a giant Kerr nonlinearity in zero linear and nonlinear probe absorption. It is shown that without coherent control field and just by quantum interference of spontaneous emission, a giant Kerr nonlinearity can be obtained.

► The quantum interference from spontaneous emission is considered in a four-level medium.
► The giant Kerr nonlinearity in the zero linear and nonlinear absorption is obtained.
► The quantum interference effect on group velocity is then investigated.