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Published January 30, 2015 | Published
Journal Article Open

Path entanglement of surface plasmons


Metals can sustain traveling electromagnetic waves at their surfaces supported by the collective oscillations of their free electrons in unison. Remarkably, classical electromagnetism captures the essential physics of these 'surface plasma' waves using simple models with only macroscopic features, accounting for microscopic electron–electron and electron–phonon interactions with a single, semi-empirical damping parameter. Nevertheless, in quantum theory these microscopic interactions could be important, as any substantial environmental interactions could decohere quantum superpositions of surface plasmons, the quanta of these waves. Here we report a measurement of path entanglement between surface plasmons with 95% contrast, confirming that a path-entangled state can indeed survive without measurable decoherence. Our measurement suggests that elastic scattering mechanisms of the type that might cause pure dephasing in plasmonic systems must be weak enough not to significantly perturb the state of the metal under the experimental conditions we investigated.

Additional Information

© 2015 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author (s) and the title of the work, journal citation and DOI. Received 22 October 2014. Revised 16 December 2014. Accepted for Publication 22 December 2014. Published 30 January 2015. This work was supported by the Air Force Office of Scientific Research under MURI Awards FA9550-12-1-0488 (JSF) and FA9550-12-1-0024 (AM). Additionally, we gratefully acknowledge the Kavli Nanoscience Institute at Caltech for access to and maintenance of fabrication equipment.

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