Tip-enhanced Nano-cavity Spectroscopy and Imaging

With support from the Chemical Structure and Dynamics (CSD) program in the Division of Chemistry, Professor Markus Raschke of the University of Colorado Boulder is combining nano-scale imaging and spectroscopy with novel optical nano-cavity concepts to study elementary electronic and vibrational excitations in chemical systems. The interaction of light with a single quantum state in an atom, molecule, or solid is the most elementary step in all light-induced processes from photosynthesis to quantum sensing and information processing.

However, optically prepared quantum states rapidly dissipate into the local chemical environment. Professor Raschke and his students will apply nano-cavity enhanced imaging and spectroscopy to study these relaxations in individual nanostructures. Their discoveries could have implications for understanding non-radiative relaxation and vibrational energy flow in molecules and materials used in future quantum-based technologies.

The project will also provide research opportunities for graduate and undergraduate students and contribute to the development of a quantum-enabled STEM workforce.

Optical cavities can control light-matter interaction in the weak coupling limit and enable new hybrid states in the strong coupling regime. Despite low quality factors, the deep sub-diffraction mode volume of nano-cavities provides for enhanced spectroscopy and quantum state control of even small ensembles and single emitters. Combining scanning probe microscopy with tip-enhanced near-field spectroscopy creates a tunable nano-cavity which allows one to separate the competing dynamics of the cavity-coupled electronic and vibrational excitations.

By spectrally and spatially tuning the tip-cavity interaction, radiative and non-radiative emission can be independently controlled. Through Purcell-enhanced nano-spectroscopy this research aims to increase the quantum yield and to control exciton emission of quantum dots, as well as to resolve intra-molecular vibrational energy redistribution in molecular nano-ensembles.

Further, by combining the tip-enhanced nano-cavity with multi-resonant antenna coupling to achieve vibrational strong coupling, the project will address the nature of dark states and provide new pathways for vibrational quantum coherent control. The work will answer questions of the fundamental limit of quantum coherence and dissipation at the elementary scale of electronic wavefunctions and vibrations in chemical systems, and it has direct applications in quantum chemistry, molecular spectroscopy, and materials science, with industry collaborations, and student workforce training.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.