Quantum theory of photon emission in current-driven single-molecule tunnel junctions

PhD Program

Speaker

Andrés Bejarano

When

2025/12/12
14:00

Place

CFM Auditorium, Donostia / San Sebastián

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PhD Thesis defense by Andrés Bejarano

Supervisor: Thomas Frederiksen (DIPC, Ikerbasque Research Professor)

Quantum / Quantum Systems and Technologies

Current driven light emission from individual molecules has attracted increasing attention in recent years, as it provides a unique platform to explore quantum processes at the nanoscale. Among the different types of tunnel junctions, the Scanning Tunneling Microscope (STM) stands out for its ability to inject electrons with atomic precision, enabling the observation of current-induced molecular electroluminescence. Remarkably, these STM-based system scan emit photons with distinct statistical properties, ranging from antibunching—where photons are emitted one by one—to superbunching—where they appear in correlated bursts.

This thesis develops a theoretical framework to understand such phenomena by describing the coupled dynamics of electrons, molecular excitations, and localized plasmons within an open quantum-system approach. In the first part, we analyze a two-level molecular model coupled to a single plasmonic mode and identify three emission regimes determined by the interplay between plasmon damping, coupling strength, and cooperativity. In the second part, we revisit a single-level model where tunneling electrons interact with a damped plasmon. By relaxing previous assumptions, we uncover a variety of photon statistics—from antibunching to superbunching—controlled by the bias voltage and tunneling asymmetry.

Overall, the results show how quantum-optical behavior naturally emerges from electronic transport at the molecular scale, offering new perspectives for the design of electrically driven nanoscale light sources.