Super-Coulombic dipole-dipole interactions in hyperbolic metamaterials

Wednesday, March 15, 2017 - 2:00pm - 2:50pm
Keller 3-180
Ward Newman (Purdue University)
Zero point fluctuations of the electromagnetic radiation field have profound effects on the electronic states of atoms and molecules. 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, Förster resonance energy transfer). The control and modification of vacuum fluctuations to engineer the dipole-dipole interactions' rapid scaling with distance has become a long-standing theme in quantum engineering since dipole-dipole interactions govern a variety of modern applications of physics (quantum computing and cryptography), engineering (harnessing van der Waals forces), and biology (FRET). In this work, our experiments show that nanostructured metamaterials can be used to engineer long-range dipole-dipole interactions.

Our approach utilizes the unique photonic modes and intrinsically broadband nature of hyperbolic metamaterials which fundamentally extend the non-radiative near-fields of dipole-dipole interactions. Dipole-dipole interactions are not directly related to the photonic density of states that govern spontaneous emission, 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 an order of magnitude 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. Measurements of time resolved emission kinetics of Förster Resonance Energy Transfer (FRET) across a 100 nm nano-fabricated hyperbolic metamaterial reveal unique signatures of resonant dipole-dipole interaction strengths four-orders of magnitude larger than any conventional material.