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cQED Susceptibility of Superconducting Transmons coupled to a Microstrip Resonator Cavity

cQED Susceptibility of Superconducting Transmons coupled to a Microstrip Resonator Cavity. David Pappas, Martin Sandberg, Jiansong Gao , Michael Vissers NIST, Boulder, CO 80303 Anton Kockum , Goran Johansson Chalmers University of Technology, G ӧ teborg , Sweden.

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cQED Susceptibility of Superconducting Transmons coupled to a Microstrip Resonator Cavity

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  1. cQED Susceptibility of Superconducting Transmons coupled to a Microstrip Resonator Cavity David Pappas, Martin Sandberg, JiansongGao, Michael Vissers NIST, Boulder, CO 80303 Anton Kockum, Goran JohanssonChalmers University of Technology, Gӧteborg, Sweden

  2. OutlineWhat 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

  3. “2½D” - Transmon coupled to microstrip cavity • Standard large-pad transmon, GHz • Measured with microstrip cavity • Measured at 20 mK • Radiation decay suppressed due to proximity of ground plane • T1 2 - 10 s • Coupling strength MHz • = 6.525 Ghz • Lifetime strongly Purcell limited • In resonant regime (not dispersive) Qubit Sandberg, et al., APL 102, 072601 (2013)

  4. Cavity response to a probe tone probe • Measure transmission, S21 at T∽100 mK • Susceptibility of the system • frequency & power dependence • High power – bare cavity • Low power – excitation spectrum of “singly dressed” qubit+cavity VNA S21 2 1 cavity High power Low power Qubit-cavity excitations

  5. Model with Jaynes-Cummings Hamiltonian Excitation spectrum • Include 4 lowest qubit states, ,,, 3 lowest photon numbers in cavity, ,,

  6. Line identification cavity cavity 0-2 3-7 1-4 • Use low power probe tone to measure the system • Add high power drive (i.e. pump) for susceptibilty

  7. Susceptibility measurement drive probe VNA S21 2 1 Drive tone, D (GHz)

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