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Quantum Interference and Entanglement of Surface Plasmons


Fakonas, James Spencer (2015) Quantum Interference and Entanglement of Surface Plasmons. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z9MG7MD3.


Surface plasma waves arise from the collective oscillations of billions of electrons at the surface of a metal in unison. The simplest way to quantize these waves is by direct analogy to electromagnetic fields in free space, with the surface plasmon, the quantum of the surface plasma wave, playing the same role as the photon. It follows that surface plasmons should exhibit all of the same quantum phenomena that photons do, including quantum interference and entanglement.

Unlike photons, however, surface plasmons suffer strong losses that arise from the scattering of free electrons from other electrons, phonons, and surfaces. Under some circumstances, these interactions might also cause “pure dephasing,” which entails a loss of coherence without absorption. Quantum descriptions of plasmons usually do not account for these effects explicitly, and sometimes ignore them altogether. In light of this extra microscopic complexity, it is necessary for experiments to test quantum models of surface plasmons.

In this thesis, I describe two such tests that my collaborators and I performed. The first was a plasmonic version of the Hong-Ou-Mandel experiment, in which we observed two-particle quantum interference between plasmons with a visibility of 93 ± 1%. This measurement confirms that surface plasmons faithfully reproduce this effect with the same visibility and mutual coherence time, to within measurement error, as in the photonic case.

The second experiment demonstrated path entanglement between surface plasmons with a visibility of 95 ± 2%, confirming that a path-entangled state can indeed survive without measurable decoherence. This measurement suggests that elastic scattering mechanisms of the type that might cause pure dephasing must have been weak enough not to significantly perturb the state of the metal under the experimental conditions we investigated.

These two experiments add quantum interference and path entanglement to a growing list of quantum phenomena that surface plasmons appear to exhibit just as clearly as photons, confirming the predictions of the simplest quantum models.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:quantum plasmonics, surface plasmon, quantum interference, path entanglement
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Applied Physics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Atwater, Harry Albert
Group:Kavli Nanoscience Institute
Thesis Committee:
  • Atwater, Harry Albert (chair)
  • Fultz, Brent T.
  • Johnson, William Lewis
  • Faraon, Andrei
Defense Date:20 November 2014
Record Number:CaltechTHESIS:12052014-101005469
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:8736
Deposited By: James Fakonas
Deposited On:09 Jan 2015 16:56
Last Modified:08 Nov 2023 00:12

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