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Complex photon-phonon coupling

Periodic Reporting for period 1 - COPPOLa (Complex photon-phonon coupling)

Reporting period: 2016-06-01 to 2018-05-31

Optomechanical crystals are purposely designed fabricated semiconductor nanostructures to enhance the coupling between the electromagnetic field and the mechanical vibrations of
matter at the nanoscale. The standard approach to do this is by creating a defect in an otherwise periodic structure, it is possible to co-localized both fields, electromagnetic and mechanical displacement, to optimize their coupling. However, in real optomechanical crystals, fabrication imperfections with respect to the ideally design structure open extra leaky channels where the transfer of energy is lost, reducing the optomechanical coupling efficiency.

In this project, we wanted to quantify the role of disorder in a paradigmatic one-dimensional optomechanical crystal with full phononic and photonic bandgaps. By adding imperfections to the ideal structure in a controllable way, we are able to explore the effect of disorder in the optomechanical coupling and the robustness of these structures against disorder. In addition, we want to show how disorder can be exploited as a resource to enhance the optomechanical coupling beyond engineered structures, thus providing a new toolset for optomechanics.
During the first months of the project, we have develope a calculation tool to analyze the role of disorder in optomechanical crystals. The codes developed can be used to explore the statistics of the modes in the regime of Anderson localization, which requires a statistical analyysis. This allows us to present a numerical analysis of Anderson localization in optomechanical crystals with particula attention to phonon localization which opens the possibility to study the role of polarization in Anderson localization. These calculations demonstrate an alternative route to explore optomechanical coupling at the nanoscale well beyond the state-of-the art where imperfections play a central role. In particular, we calculated the vacuum optomechanical coupling rate between disorder-induced modes that overcome the coupling rate of engineered cavity modes.

These calculations have been reported in a manuscript accepted for publication in Phys. Rev. B

Based on these calculations, we have designed the layout for electron beam lithography and the nanostructures have been fabricated. Preliminary characterization of the nanostructures show Photonic Anderson localization. We are focusing now on measuring the optomecahncial coupling.
We have explored the optomechanical coupling in the regime of Anderson localization for the first time. Controlling Anderson localization in these nanostructures can also bring innovative
solutions to open issues in a broad range of scientific disciplines, e.g. slowing down the dephasing time scale of spin qubits or even for thermal insulation at very low temperatures (mK).
An ultrafast optical technique will be used in the project COPPOLA to measure Anderson-localized mo