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**KOÇ UNIVERSITY PHYSICS SEMINAR**

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**Speaker ** : Hakan Türeci, Princeton University

**Title ** : Divergence-free Circuit Quantum Electrodynamics

**Date ** : May 29, 2018

**Time** : 14:30

**Cookie & Tea** : SCI 103 14:15

**Place** : SCI 103

**web **: https://physics-seminars.ku.

**Abstract:
**Any quantum-confined electronic system coupled to the electromagnetic continuum is subject to radiative decay and renormalization of its energy levels. When inside a cavity, these quantities can be strongly modified with respect to their values in vacuum. In the planar circuit quantum electrodynamics architecture the radiative decay rate of a Josephson Junction qubit is strongly influenced by far off-resonant modes. A multimode calculation including all cavity modes however leads to divergences unless a cutoff is imposed. It has so far not been identified what the source of divergence is, or whether the divergence is a fundamental issue. I will show that unless gauge invariance is respected, any attempt at the calculation of circuit QED quantities is bound to diverge. I will then discuss an internally consistent theoretical and computational framework based on a Heisenberg-Langevin approach to the calculation of a finite spontaneous emission rate and the Lamb shift in an arbitrarily complex electromagnetic environment, that is free of cutoff.

**Short Bio: **Hakan E Tureci is an Associate Professor in the Department of Electrical Engineering at Princeton University. Prior to joining Princeton faculty, he obtained his B.S. (Physics) from Bilkent University and received his Ph.D. (Physics) from Yale University in 2003. He did his postdoctoral work at Yale University and at ETH Zurich. In 2009, he was appointed SNF Professor at ETH. He moved to Princeton University in 2010. His research focuses on theoretical problems in quantum optics, photonics and lasers, in particular non-equilibrium dynamics in classical and quantum collective systems. He is the recipient of the NSF CAREER Award and the DARPA Young Faculty Award.