Anti-coalescence of bosons on a lossy beam splitter

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Science  30 Jun 2017:
Vol. 356, Issue 6345, pp. 1373-1376
DOI: 10.1126/science.aam9353

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To bunch or to antibunch

Particles of matter can be classed as either as bosons or fermions. Their subsequent behavior in terms of their physical properties and interactions depends on which quantum statistics they obey. Photons, for instance, are bosons and tend to bunch. Electrons are fermions and tend to antibunch. Vest et al. show that surface plasmon polaritons, a hybrid excitation of light and electrons, can exhibit both kinds of behavior (see the Perspective by Faccio). By tuning the level of loss in their system, bunching and antibunching of interfering plasmons can be seen.

Science, this issue p. 1373; see also p. 1336


Two-boson interference, a fundamentally quantum effect, has been extensively studied with photons through the Hong-Ou-Mandel effect and observed with guided plasmons. Using two freely propagating surface plasmon polaritons (SPPs) interfering on a lossy beam splitter, we show that the presence of loss enables us to modify the reflection and transmission factors of the beam splitter, thus revealing quantum interference paths that do not exist in a lossless configuration. We investigate the two-plasmon interference on beam splitters with different sets of reflection and transmission factors. Through coincidence-detection measurements, we observe either coalescence or anti-coalescence of SPPs. The results show that losses can be viewed as a degree of freedom to control quantum processes.

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