Tunable Single-Photon Nonlinearities at Room Temperature: Polaronic Optical Gunn Effect in Individual Carbon Nanotubes

This dissertation presents a breakthrough in single-molecule spectroscopy: we successfully advanced fluorescence-detected two-dimensional electronic spectroscopy (F-2DES) to the single-molecule level, opening unprecedented opportunities for studying quantum phenomena at room temperature. We developed three complementary techniques for single-emitter validation—streamlined g²(τ) analysis, Mandel Q-parameter time-gating, and Buffon's needle stochastic modeling—enabling reliable identification of individual quantum emitters. Our central discovery is the polaronic optical Gunn effect, a novel room-temperature quantum phenomenon with transformative implications for optical computing and quantum technologies. This effect manifests when light interacts with individual carbon nanotubes, creating tunable single-photon nonlinearities that achieve amplification up to 60 dB—a crucial step toward photonic transistors operating at the quantum limit. We comprehensively explored both facets of this phenomenon: First, through nonlinear kinetic rate equations, we revealed incoherent intervalley coupling mechanisms governing electron transport in the phonon sideband. Second, using single-molecule F-2DES and our newly developed PPI2D (polaron-polaron interaction two-dimensional spectroscopy), we uncovered coherent coupling between polaron states with J=38 meV, mediated by specific phonons and leading to bipolaron formation with binding energy E_B=39 meV. The power of our approach lies in its universal applicability—while demonstrated on carbon nanotubes, these methods can probe quantum objects across diverse material systems. By elucidating the coupling phenomena that drive nonlinear amplification and Gunn behavior at the single-molecule level, this work establishes the foundation for next-generation quantum devices operating at room temperature, bridging fundamental physics with practical applications in computing with light. The results have profound implications for THz optoelectronics, high-temperature superconductivity, 6G and space communications, initiating a transformative synergy between photonics and polaronic phenomena in electron transport.