Cavity optomechanics allows the control of mechanical motion through the radiation-pressure interaction and has contributed to the quantum control of engineered mechanical systems ranging from kilogram-scale laser interferometer Gravitational-wave Observatory (LIGO) mirrors to nanomechanical systems. Still, almost all previous schemes have used single- or single-mode optomechanical systems.
Leading theoretical research has projected that optomechanical gratings can access significantly more complex physics and unique dynamics, such as quantum collective dynamics and topological phenomena. However, it has proven difficult to create optomechanical gratings that can support numerous coupled optical and mechanical degrees of freedom and to experimentally duplicate such devices under strict control.
The first large-scale and reconfigurable optomechanical lattice of superconducting circuits that can solve the scaling problems of quantum optomechanical systems has been created by scientists in Tobias J. Kippenberg’s lab at EPFL’s School of Basic Sciences. The team realized an optomechanically strained graphene lattice and used advanced measurement methods to investigate non-trivial topological edge states.
A “vacuum-gap drum-head capacitor,” also a critical part of the grid’s single site, consists of a thin aluminum film suspended over a slot in a silicon substrate. This forms the vibrating component of the device and at the same time creates a resonant microwave circuit with a helical inductor.
Amir Youssefi, who led the project, said: “We have developed a new nanofabrication technique for optomechanical systems of superconducting circuits with high reproducibility and extremely tight tolerances for the parameters of the individual devices. This allows us to make the different locations almost identical, as in a natural lattice.”
The graphene lattice is known to exhibit non-trivial topological features and localized edge states. These states were seen in what the scientists call an “optomechanical graphene flake,” made up of twenty-four spots.
Andrea Bancora, who contributed to the research, said: “Thanks to the built-in optomechanical toolkit, we were able to visualize the collective electromagnetic mode shapes in such gratings directly and non-distortively. That is unique to this platform.”
Their new platform provides a reliable testbed for topological physics research in one- and two-dimensional grids, as evidenced by the team’s results, which closely match theoretical predictions.
Shingo Kono, another member of the research team, said: “By accessing both the energy levels and mode shapes of these collective excitations, we were able to reconstruct the full underlying Hamiltonian of the system, allowing for the first time the full extraction of disorder and coupling strengths in a superconducting lattice. “
- Youssefi, A., Kono, S., Bancora, A. et al. Topological lattices realized in optomechanics of superconducting circuits. Nature 612, 666-672 (2022). DOI: 10.1038/s41586-022-05367-9