Kirchmair, Gerhard

Date:    Wednesday, November 29, 2023
Time:    11:00
Place:    ETH Campus Hönggerberg, HPF G 6
Host:    Yiwen Chu 

Coherent control of a symmetry-engineered multi-qubit dark state in waveguide quantum electrodynamics

Gerhard Kirchmair - Institute for Experimental Physics, University of Innsbruck, Austria; IQOQI Innsbruck, Austria

Abstract: In this talk I will introduce, how we use a circuit quantum electrodynamics architecture to realize a platform for building small interacting quantum many body systems. Our basic building blocks are transmon qubits, where we use the naturally occurring dipolar interactions to realize interacting spin systems. Additionally, these qubits can be coupled strongly to a microwave waveguide, which allows us to study open system dynamics with interacting spin systems. Using these building blocks, we have engineered a four-qubit system combining a direct dipole-dipole with waveguide-mediated interactions to form collective sub-radiant (dark) and super-radiant (bright) states. The dark state’s protection against decoherence results in a decay time that exceed those of the waveguide limited single qubits by more than two orders of magnitude. The bright state can be used to read out the encoded qubit. We show experimentally that this four-qubit dark-state can be coherently controlled by utilizing a driving scheme relying on the symmetries of the quantum states. Furthermore, this coherent control allows us to perform phase sensitive spectroscopy on the higher excitation manifold revealing bosonic many-body statistics in the transmon array. In the future such a platform can be used to mediate entanglement between remote parts of a superconducting qubit quantum processor and implement quantum information protocols with collective states.