Experimental Demonstration of Engineered Dipole-Dipole Interactions in Nanophotonic Environments

Ward D Newman, Purdue University

Abstract

Zero point fluctuations of the electromagnetic radiation field have profound effects on the electronic states of atoms and molecules. For example, vacuum fluctuations of the photonic radiation field stimulate the spontaneous decay of excited states of atoms (spontaneous emission), shift atomic energy levels (Lamb Shift), and allow nearby atoms and molecules to couple via dipole-dipole interactions (van der Waals interactions, Casimir effect, super radiance, F"{o}rster resonance energy transfer). The control and modification of vacuum fluctuations has been a long-standing theme in quantum engineering as one can then truly control single photon emission and alter dipole-dipole interactions spatial scaling with distance. The ability to do so would have far reaching impacts in physics (quantum computing and cryptography), engineering (harnessing van der Waals forces), and bio-imaging. In this thesis we leverage the emerging new technology of metamaterials to design and fabricate devices that facilitate strong light matter interactions and allow for long-range dipole-dipole interactions among quantum emitters. Our approach utilizes the unique photonic modes and intrinsically broadband nature of hyperbolic metamaterials, uniaxial media with extreme anisotropy. We show experimentally that hyperbolic media fundamentally extend the non-radiative near-fields of dipole-dipole interactions. In conventional media, these non-radiative near-fields decay dramatically with distance curtailing interactions to only a few nanometers. This first experimental demonstration was achieved through synergistic advances in theory, ultrafast optics, low-light level detection and nanofabrication. We find that dipole-dipole interactions are not directly related to the photonic density of states, but instead are quantified by the two-point spectral density function, a physical quantity distinct from the photonic density of states. We engineer this quantity and construct a metamaterial device that displays dipole-dipole interactions far beyond the range of the conventional Coulombic near-field, achieving Super-Coulombic Dipole Interactions. Our approach is distinct from existing techniques which generally rely on narrow band resonant cavities or band edge photonic crystals to engineer the radiative far-field interactions. We also design a hyperbolic metamaterial device to enhance and direct the spontaneous emission from isolated fluorescent emitters. Stimulating experimental evidence demonstrates that hyperbolic metamaterials are viable candidates for enhancing single photon emission into well defined spatial modes. This thesis also describes rigorous metamaterial fabrication and design principles, and presents experimental isolation of unique Ferrel-Berreman modes in epsilon-near-zero media which are radiative collective charge oscillations in ultrathin films. Finally, we make advancements in nanofabrication of disordered plasmonic media that achieves localized plasmonic resonances to demonstrate giant enhancement in many-body dipole-dipole interactions. From experiments, we infer that the normally spherically symmetric near-field Coulombic potential is anisotropic above disordered gold nano-particle substrates. We envision that controlled dipole-dipole interactions can impact deterministic entanglement creation between remote emitters, quantum coherence in metamaterial mediated photosynthetic energy transfer, lead to many-dipole interactive states in metamaterials, increase the range of biomolecular FRET rulers as well as FRET imaging systems, and accelerate progress towards the long-standing goal of strongly coupled quantum systems at room temperature (Vdd > kBT room).

Degree

Ph.D.

Advisors

Jacob, Purdue University.

Subject Area

Nanoscience|Nanotechnology|Optics

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