Electromagnetically Induced Superluminal Light in a 3D Transmon Device

Quantum interference in a three level $\Lambda $-type system can result in non-linear optical effects such as electromagnetically induced transparency/absorption (EIT/EIA), slow, and fast light. We have created a $\Lambda $ system with an effectively metastable state by dispersively coupling an Al/AlOx/Al transmon qubit (T1 $=$4 us) to a 3D Cu microwave cavity (T1$=$340ns). By probing the transmission through the cavity while pumping a qubit-cavity sideband yields a large change in the dispersion. We observe group advances of up to 10 us for Gaussian pulses propagating through the system, corresponding to a group index of -176,000.