Coherent Manipulation of Atomic-Scale Defects in Amorphous Oxide
Prof. Dr. Alexey Ustinov (KIT, Karlsruhe)

In structurally disordered solids, some atoms or small groups of atoms are able to quantum mechanically tunnel between two nearly equivalent sites. These atomic tunneling systems have been identified as the cause of various low- temperature anomalies of bulk glasses and as a source of decoherence of superconducting quantum circuits where they are sparsely present in the disordered oxide barriers of Josephson junctions. A tiny deformation of the oxide barrier changes the energies of the atomic tunneling systems. We have measured these changes by microwave spectroscopy of the superconducting qubit through coherent interaction between the macroscopic qubit and the microscopic atomic tunneling system. By tracing the dependence of the energy splitting of atomic tunneling states on external strain, we have for the first time directly verified a central hypothesis of the two-level tunneling model for disordered solids.