Our group is interested in understanding how light and matter interacts and behaves in extreme local electromagnetic fields, and in harnessing the resulting unprecedented optical properties for transformative technologies. New nanomaterials hold the potential for breakthroughs in a wide range of areas from ultrafast optoelectronics such as modulators, light sources and hyperspectral detectors, to efficient upconversion for energy applications, bio-sensing and on-chip components for quantum information science; they also serve as inspiration for entirely new devices and technologies. An exciting opportunity to realize such new nanomaterials lies in controlling the local electromagnetic environment on the atomic- and molecular-scale, (~1-10 nm) which enables extreme field enhancements, but represents a largely unexplored length scale. Creative nanofabrication techniques at the interface between chemistry and physics are essential to experimentally realize this new regime, together with advanced, ultrafast optical techniques to probe the emerging phenomena. 

Recently, we have shown that designing and assembling composite materials from the bottom-up with molecular-scale resolution allows us to delve into uncharted territories for creating extreme local field enhancements that enable dramatically improved optical properties of embedded emitters or semiconductor materials. In particular, we demonstrated record-high enhancements in the spontaneous emission rate of dye molecules (Purcell factors > 1000) and semiconductor quantum dots coupled to plasmonic nanocavities pointing towards ~100 GHz spontaneous emission sources [Nature Photonics 2014, Nature Communications 2015]. Based on these ideas, we also experimentally realized the long-sought goal of an ultrafast single photon source [Nano Letters 2016], which is an important milestone for the quantum information science and quantum optics communities. In addition to modification of spontaneous emission rates, we showed strongly tailored absorption rates, quantum efficiencies, and radiation patterns leading to four orders of magnitude fluorescence enhancements [Nano Letters 2014], efficient near-IR emitters [ACS Photonics 2016] and tailored emission from monolayer MoS2 [Nano Letters 2015, ACS Photonics 2018]. This reveals that even well-known materials that have been studied for decades can take on entirely new behavior by sculpting their environment, and that control of critical dimensions on a single-nanometer scale is essential. For technology transfer, a patent filed based on this research has already been licensed and industry collaborations and support are on-going (Connectivity Lab, Facebook). 

Leveraging this new insight about the importance of atomic- and molecular-scale control, we used chemical techniques to realize tunable, spectrally selective perfect absorber surfaces [Advanced Materials 2015, Nano Letters 2018], multi-spectral pixels and ~10,000 plasmonic combinatorial colors [Advanced Materials 2017]. These results are promising for transformative breakthroughs of the performance and versatility of e.g., photodetectors, imaging devices, and advanced coatings. 

Future directions

In the future, we see even larger potential breakthroughs by exploiting these ideas to precisely mold the local electromagnetic fields—with single nanometer precision—to control and tailor quantum and nonlinear optical processes and bring new insights into their behavior in such extreme environments. To generate a broader impact, it is vital to understand how such breakthroughs in material response translate to more complex nanostructures, perform in proof-of-concept devices, and impact other scientific fields. Thus, our research is focused on three areas, all exploiting extreme field enhancements: 1) Quantum effects including on-chip indistinguishable entangled photon pairs, on-chip coupling of ultrafast single photon sources, strong coupling, and exciton polariton condensates. 2) Nonlinear plasmonics where the strong field enhancements are well-suited to enhance weak nonlinear processes that depend superlinearly on the local field intensity. Spontaneous parametric down-conversion and ultrafast modulation utilizing Kerr-type nonlinearities are examples of processes that will be studied. 3) Exploration of optoelectronic and sensing applications utilizing the unique material properties revealed in other projects. Examples include hyperspectral imaging, ultrafast transmitters and receivers for free-space optical communications, and plasmonically enhanced point-of-care detection of biomarkers.