Invited Paper
Quantum Manipulation of Single and Several Plasmons

Harry A. Atwater Applied Physics, California Institute of Technology, Pasadena, California, USA Joint Center for Artificial Photosynthesis, California Institute of Technology, Pasadena, California, USA James Fakonas Applied Physics, California Institute of Technology, Pasadena, California, USA Anya Mitskovets Applied Physics, California Institute of Technology, Pasadena, California, USA Prineha Narang Applied Physics, California Institute of Technology, Pasadena, California, USA Joint Center for Artificial Photosynthesis, California Institute of Technology, Pasadena, California, USA Ravishankar Sundaraman Joint Center for Artificial Photosynthesis, California Institute of Technology, Pasadena, California, USA William Goddard III Joint Center for Artificial Photosynthesis, California Institute of Technology, Pasadena, California, USA Yury Tokpanov Applied Physics, California Institute of Technology, Pasadena, California, USA

Classical models of surface plasma waves usually account for the microscopic scattering effects responsible for loss using a single, semi-empirical Drude damping parameter. However in the quantum mechanical realm, surface plasmon quanta, playing an analogous role to quantum states of photons. Experiments in the last several years have begun to test this analogy, demonstrating single-particle statistics, squeezing, entanglement, and quantum interference in plasmonic circuits. Moreover plasmon decay can produce a variety of excited particle states, partitioning plasmon energy between `hot` electrons and holes.

We report entanglement of plasmons in chip-based integrated structures, via two-photon quantum interference in plasmonic waveguide directional couplers, and path entanglement in photonic circuits using thermo-optic phase shifters for phase tuning. We observed path entanglement between surface plasmons with a visibility of approximately 95%. As a result, we conclude that the plasmons in our experiment did not interact strongly enough with the metal to decohere the path-entangled state. We also discuss further the implications of plasmon coherence for use of plasmonic confinement in quantum information processing.

The decay of surface plasmon resonances is usually a detriment in the field of plasmonics, but the possibility of capturing the energy normally lost to heat has potential to open new directions for photonic and energy conversion devices. In the context of hot-electron devices, the large extinction cross-section at a surface plasmon resonance enables nanostructures to absorb a signi cant fraction of the incident spectrum in very thin fi lms. Despite the signi cant experimental work in this direction,comprehensive theoretical understanding of plasmon-driven hot carrier generation with electronic structure details has been elusive. We have analyzed the quantum decay of surface plasmon polaritons and found that the prompt distribution of generated carriers is extremely sensitive to the energy band structure of the plasmonic material. We present results on partitioning of energy and momentum between excited electrons and holes for Cu, Ag, Al and Au and discuss implications for hot carrier transport in plasmonic nanostructures.

haa@daedalus.caltech.edu









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