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Quantum Plasmomechanics with THz Phonons and Molecular Nano-junctions

Periodic Reporting for period 3 - QTONE (Quantum Plasmomechanics with THz Phonons and Molecular Nano-junctions)

Reporting period: 2022-08-01 to 2024-01-31

This project address the issue of whether vibrational modes of molecules and 2D materials can be amplified and driven into the nonlinear regime by weak optical excitation, using the high field enhancement and sharp resonances provided by optimised plasmonic nanocavities.
The importance for society lies in the development of nanoscale devices for nonlinear optics, as well as the control of chemical reaction using light.
The overall objectives are to improve our understanding of light-matter interaction inside plasmonic nanocavities, with the specific aim to amplify molecular vibration by optical driving of a plasmonic cavity.
In the TecQ sub-project, we achieved the first demonstration of photon-phonon Bell correlations at ambient conditions and measured the dynamics of photon-phonon decoherence with 200 fs time resolution (work published in Dec. 2020 in Science Advances, gold open access). In addition, we are about to submit a manuscript in which we observe quantum beats in the Stokes – anti-Stokes correlations measured on the molecular liquid CS2 that reveal the presence of entanglement between two vibrational modes with shifted eigenfrequencies (see Fig. 2 from part B2 of the proposal).
In the sub-project DyBa, our efforts focused on developing a deeper understanding of nanoparticle-on-mirror (NPoM) plasmonic cavities. In the process, we discovered an unexpected fluctuation in the gold-induced luminescence, which we called intrinsic luminescence blinking. This work was spearheaded by a postdoc from my group working on a different EU-funded project (THOR, FET Open), but also significantly involved two PhD students working on the QTONE ERC project: Sachin Verlekar and Aqeel Ahmed. The manuscript will be published soon in Nature Communication (gold open access). Ongoing manuscript are investigating the subtle interplay between molecular layer morphology and nanocavity stability, as well as the dynamics and origin of so-called “pico-cavities” in which optomechanical gain was first reported (Science 2016). We are also finalising a study on Raman sideband thermometry in NPoM cavities (PhD student Valeria Vento)
In the sub-project SMol, involving PhD student Sakthi Pryia Amirtharaj and a close collaboration with Emanuel Loertscher at IBM Research Switzerland, we are approaching the first experimental results. We have so far built the optical and transport measurement setup around the mechanical break-junction device leased to us by Dr. Loertscher. The fabrication of a first batch of mechanically actuated nano-antennas with contacts should be completed soon at IBM. In the meanwhile, we are developing a different approach based on directed assembly of nanoparticle inside nanogaps, whose fabrication is done fully at EPFL.
Until the end of the project, we expect to have understood and controlled the vibrational and electronic dynamics occurring in plasmonic nanocavities on time scales ranging from 100 fs to hours. It will be achieved using a combination of ultrafast and continuous wave optical techniques and transport measurements.
Intrinsic luminescence blinking discovered in plasmonic nanocavities