Figure 2.

Four-level QD with the two upper levels |c〉 and |b〉 which are near one another, and two lower levels |a〉 and |d〉. Here, ω is the probe field frequency while ωca and ωba are the transition frequencies.Γc and Γb are the decay rates from the exited states to the |a〉 state. The decay rate from |a〉 to |d〉 is given as Γa, whereas Δc = ωcaω and Δb = ωωba are the detunings of the atomic transition energies.δk is the detuning of the probe field, which has a central frequency at the middle point of the two upper levels

Hatef and Singh Nanoscale Research Letters 2010 5:464-468   doi:10.1007/s11671-009-9517-1