Dresden 2020 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 55: Superconducting Electronics: SQUIDs, Qubits, Circuit QED, Quantum Coherence and Quantum Information Systems 2 (jointly with MA, HL) (joint session TT/HL)
HL 55.1: Talk
Thursday, March 19, 2020, 09:30–09:45, HSZ 03
Waveguide Bandgap Engineering with an Array of Superconducting Qubits — •Jan David Brehm1, Alexander N. Poddubny2, Alexander Stehli1, Tim Wolz1, Hannes Rotzinger1,3, and Alexey V. Ustinov1,4,5 — 1Physikalisches Institut, Karlsruher Institut für Technologie, Karlsruhe, Germany — 2Ioffe Institute, St. Petersburg, Russia — 3Institut für Festkörperphysik, Karlsruher Institut für Technologie, Karlsruhe, Germany — 4National University of Science and Technology MISIS, Moscow, Russia — 5Russian Quantum Center, Skolkovo, Moscow, Russia
In one dimension the interaction of qubits with free space instead of a cavity gives rise to an effective qubit-qubit coupling which is of infinite range and can be tuned by varying the qubit separation. In this work, we experimentally study an array of eight superconducting transmon qubits with local frequency control, which are all coupled to the mode continuum of a superconducting waveguide. The spacing between adjacent qubits is substantially smaller than the wavelength corresponding to their excitation frequency, eliminating almost completely the coherent exchange type interaction between qubits. By consecutively tuning the qubits to a common resonance frequency we observe the formation of super- and subradiant states as well as the emergence of a bandgap. Furthermore, we study the nonlinear saturation of the collective modes with increasing photon number and electromagnetically induce a transparency window in the bandgap region of the ensemble.