Multi-mode ultra-strong coupling in circuit quantum electrodynamics
Sal J. Bosman (Kavli institute of nanoscience Delft, TU Delft - QN/Steele Lab)
M. F. Gely (Kavli institute of nanoscience Delft, TU Delft - QN/Steele Lab)
Vibhor Singh (Indian Institute of Science)
A Bruno (TU Delft - QuTech Advanced Research Centre, TU Delft - QCD/DiCarlo Lab)
Daniel Bothner (TU Delft - QN/Steele Lab, Kavli institute of nanoscience Delft)
Gary Steele (TU Delft - QN/Steele Lab, Kavli institute of nanoscience Delft)
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Abstract
With the introduction of superconducting circuits into the field of quantum optics, many experimental demonstrations of the quantum physics of an artificial atom coupled to a single-mode light field have been realized. Engineering such quantum systems offers the opportunity to explore extreme regimes of light-matter interaction that are inaccessible with natural systems. For instance the coupling strength g can be increased until it is comparable with the atomic or mode frequency ωa,m and the atom can be coupled to multiple modes which has always challenged our understanding of light-matter interaction. Here, we experimentally realize a transmon qubit in the ultra-strong coupling regime, reaching coupling ratios of g/ωm = 0.19 and we measure multi-mode interactions through a hybridization of the qubit up to the fifth mode of the resonator. This is enabled by a qubit with 88% of its capacitance formed by a vacuum-gap capacitance with the center conductor of a coplanar waveguide resonator. In addition to potential applications in quantum information technologies due to its small size, this architecture offers the potential to further explore the regime of multi-mode ultra-strong coupling.
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