APPLIED PHYSICS GRADUATE PROGRAMJoint PhD Program Between Weinberg College and Mccormick School of Engineering

Research Interests

Research in Koch's group focuses on theoretical condensed matter physics, quantum optics, and quantum information.

Driven by a lively interest in strongly correlated quantum systems, quantum information processing with solid-state devices, and quantum coherence in mesoscopic systems, a central theme of research in Koch’s group is the study of artificial quantum systems: man-made systems that behave quantum mechanically and that can be used to explore new quantum effects not realized in nature. The advent of such quantum systems (e.g. quantum dots, single-molecule transistors and superconducting qubits) has dramatically shifted our perspective on quantum mechanics from a theory used “passively” to calculate properties of nature-given objects like atoms and solids, to an “active” field in which quantum systems with desired properties can be designed, manipulated in a controlled way, and in the future possibly used in applications such as quantum computation.

Koch has made significant contributions to recent advances with superconductingqubits and circuit quantum electrodynamics (cQED). Such superconducting circuits, patterned on microchips, represent an exciting type of artificial quantum system that is very versatile, tunable, and that can be controlled and measured by using microwave signals. Koch has been involved in cQED research and development of advanced superconducting devices such as the transmon and fluxonium devices, and has co-authored several key papers including the 2007 demonstration of the first two-qubit gates in cQED.

Encouraged by recent experimental progress with the fluxonium device, the first superconducting circuit including a a Josephson junction array (more than 40 junctions) with coherence times of up to ~10 microseconds, current research in Koch’s group explores complex superconducting circuits and their potential for increased coherence and topological protection.  The second thrust of research is based on the intriguing idea that arrays of coupled cQED systems can open a new path to studying strongly correlated systems of photons or polaritons. In addition to local efforts and collaborations at Northwestern, Koch also collaborates closely with the experiental group of Andrew Houck at Princeton.

Selected Publications

A. A. Houck, H. E. Türeci, and J. Koch, On-chip quantum simulation with superconducting circuits, Nature Phys. 8, 292–299 (2012).

A. Nunnenkamp et al., Synthetic gauge fields and homodyne transmission in Jaynes-Cummings lattices, New J. Phys. 13, 095008 (2011).

G. Catelani, J. Koch, L. Frunzio, R. J. Schoelkopf, M. H. Devoret, and L. I. Glazman,Quasiparticle relaxation of superconducting qubits in the presence of flux, Phys. Rev. Lett. 106, 077002 (2011).

V. Manucharyan, J. Koch, L. I. Glazman, M. H. Devoret, Fluxonium: Single Cooper-Pair Circuit Free of Charge Offsets, Science 326, 113 (2009).

J. Koch, V. Manucharyan, M. H. Devoret, L. I. Glazman, Charging effects in the inductively shunted Josephson junction, Phys. Rev. Lett. 103, 217004 (2009).

J. Koch and K. Le Hur, Superfluid–Mott Insulator Transition of Light in the Jaynes-Cummings Lattice, Phys. Rev. A 80, 023811 (2009).

J. Majer et al., Coupling Superconducting Qubits via a Cavity Bus, Nature 449, 443 (2007).