Professor Koch’s research interests in theoretical condensed matter physics include strongly correlated quantum systems, quantum information processing with solid-state devices as well as transport and coherence in nanoscale systems. He explores the exciting prospects of applying quantum circuit devices as artificial atoms in quantum computation and quantum optics and, in collaboration with several experimental groups, studies coherence of novel quantum circuits. His second research thrust focuses on larger array systems composed of Josephson-junction based circuits (superconducting qubits) and superconducting microwave resonators. Polaritons in such circuit QED arrays are predicted to undergo quantum phase transitions of polaritons and may lead to quantum simulators of strongly interacting photons.