Accueil du site Séminaires Séminaire QUEST

Séminaire QUEST

Jeudi 07 juillet à 9h30,
Salle Rémy Lemaire, K223

Orateur : Martin P. Weides (Karlsruhe Institute of Technology and Johannes Gutenberg University of Mainz, Germany)
"Experiments with superconducting quantum circuits : multi-photons transitions and transmon qubits with anisotropic magnetic moment"


The experimental realization of quantum simulator and computers requires scalable and well-controllable qubits as building blocks. Superconducting quantum devices are a leading candidate for their implementation. Ideally, these quantum circuits consist of arrays of two-level-systems. Due to the lack of such idealized quantum elements their basic building element is a few-level quantum circuit.

In this talk, we report on the investigation of such a superconducting anharmonic multilevel circuit that is coupled to a harmonic readout resonator [1]. We observe multiphoton transitions via virtual energy levels of our system up to the fifth excited state. Multiphoton dressing within our anharmonic circuit yields emerging higher-order Rabi sidebands and associated Autler-Townes splitting.

Furthermore, we present a planar qubit design based on a superconducting circuit that we call concentric transmon [2]. While employing a straightforward fabrication process using Al evaporation and lift-off lithography, we observe qubit lifetimes and coherence times in the order of 10 μs. We systematically characterize loss channels such as incoherent dielectric loss, Purcell decay and radiative losses. The implementation of a gradiometric SQUID loop allows for a fast tuning of the qubit transition frequency and therefore for full tomographic control of the quantum circuit. Due to the large loop size, the presented qubit architecture features a strongly increased magnetic dipole moment as compared to conventional transmon designs. This renders the concentric transmon a promising candidate to establish a site-selective passive direct z-coupling between neighboring qubits, being a pending quest in the field of quantum simulation.

Finally, we will discuss our measurement schemes for hybrid magnons-superconducting microwave resonators / qubit systems. Exploring spin wave dynamics in thin films by coupling to a superconducting qubit complements conventional measurement techniques based on photon, electron or neutron scattering methods, which require highly populated excitations.

[1] J. Braumueller, J. Cramer, S. Schlör, H. Rotzinger, L. Radtke, O. Lukashenko, P. Yang, Sebastian T. Skacel, Sebastian Probst, M. Marthaler, L. Guo, A. V. Ustinov, and M. Weides, Phys. Rev. B 91, 054523 (2015)

[2] J. Braumueller, M. Sandberg, M. R. Vissers, A. Schneider, S. Schloer, L. Gruenhaupt, H. Rotzinger, M. Marthaler, A. Lukashenko, A. Dieter, A. V. Ustinov, M. Weides, and D. P. Pappas, Appl. Phys. Lett. 108, 032601 (2016)

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