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Date & Time: March 17 at 3:30 PM
Location: Laboratory for Physical Sciences, Seminar Room, Lower Level
Speaker: Per Delsing
Institution: Chalmers University of Technology
Title: "Fast tuning of a high-Q microwave cavity for qubit coupling and demonstration of dressed states in a superconducting qubit."
Abstract: In 2004 Wallraff et al. [1] demonstrated that an artificial atom in form of a superconducting qubit can exhibit coherent interaction with a superconducting high Q microwave transmission-line resonator. In recent experiments [2,3] similar resonators have been used for coupling and reading out qubits. In these experiments the resonance frequency of the resonator is fixed and the qubit frequency is tuned.
Here we present measurements on a superconducting transmission line resonator with a tunable resonance frequency that could be used for qubit coupling [4]. With such a device, qubit gates can be performed while the qubits stay at their optimal points during operation. We demonstrate a tunability of 700 MHz for a 4.8 GHz resonator with a line width of 500 kHz and that we can tune the resonance frequency by 330 MHz in a few ns. We show that if the resonator is detuned faster than its decay time the photons inside the resonator will shift their frequency with the resonator.
We also show how dressed states can be created in a Cooper pair box [5] and how these can be studied using a quantum capacitance read-out.
[1] A. Wallraff, D. I. Schuster, A. Blais, L. Frunzlo, R. S. Huang, J. Majer, S. Kumar, S. M. Girvin, and R. J. Schoelkopf, Nature 431, 162 (2004).
[2] J. Majer, J. M. Chow, J. M. Gambetta, J. Koch, B. R. Johnson, J. A. Schreier, L. Frunzio, D. I. Schuster, A. A. Houck, A. Wallraff, et al., Nature 449, 443 (2007).
[3] M. A. Sillanpaa, J. I. Park, and R. W. Simmonds, Nature 449, 438 (2007).
[4] M. Wallquist, V. S. Shumeiko, and G. Wendin, Physical Review B 74, 224506 (2006).
[5] C. M. Wilson, T. Duty, F. Persson, M. Sandberg, G. Johansson, and P. Delsing, Physical Review Letters 98, 257003 (2007).
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