Observation of quantum interference between a discrete quantum level and a continuum of states exploiting the Fermi edge singularity

Stephan Smolka*, F. Haupt,* B. Sbierski, W. Wüster, J. Miguel-Sanchez,  A. Imamoglu

Institute for Quantum Electronics, ETH Zurich
*These authors contributed equally to the experiment

We demonstrate experimentally a quantum inference between a discrete quantum dot energy level and a continuum of states in a nearby Fermi reservoir using resonant absorption measurements. This Fano resonance can be detected by continuously tuning the discrete quantum dot energy level with respect to the Fermi reservoir.  In the vicinity of the Fermi energy we observe - in addition to the quantum dot transition - an indirect transition that can be attributed to the Fermi edge singularity.
Both optical transitions are subjected to a tunnel-coupled broadening as well as many-body scattering leading to a highly asymmetric line shape. The experimental data are found to be in very good agreement with our theoretical model allowing us to directly determining the non-trivial phase between the discrete quantum level and the continuum of states. The quantum interference between a quantum dot and the Fermi reservoir is an important step to study unexploited many-body phenomena.