cQED Susceptibility of Superconducting Transmons coupled to a Microstrip Resonator Cavity David Pappas, Martin Sandberg, Jiansong Gao, Michael Vissers NIST, Boulder, CO Anton Kockum, Goran Johansson Chalmers University of Technology, G ӧ teborg, Sweden

Outline What do you do when your qubit frequency is too close to your cavity? “Quantum art” Response of a coupled qubit-cavity system to a strong drive at finite temperature – Singly dressed - qubit + cavity – Doubly dressed system – qubit+cavity+ drive two photon processes – Triply dressed three photon processes

“2½D” - Transmon coupled to microstrip cavity Sandberg, et al., APL 102, (2013) Qubit

Cavity response to a probe tone VNA S 21 probe 1 2 Measure transmission, S 21 at T ∽ 100 mK Susceptibility of the system frequency & power dependence High power – bare cavity Low power – excitation spectrum of “singly dressed” qubit+cavity cavity Qubit-cavity excitations High power Low power

Model with Jaynes-Cummings Hamiltonian Excitation spectrum TransitionFrequency (GHz)

Line identification TransitionFrequency (GHz) cavity Use low power probe tone to measure the system Add high power drive (i.e. pump) for susceptibilty

Susceptibility measurement VNA S 21 probe 1 2 drive Drive tone, D (GHz)