Tonomura's Single-Electron Interference
Watching the interference pattern build, one electron at a time
First published: A. Tonomura et al., "Demonstration of single-electron buildup of an interference pattern", *American Journal of Physics* 57 (1989): 117–120.
Electrons fired one at a time at a biprism build, dot by dot, into an interference pattern over 28 minutes of exposure. Each electron interferes with itself.
Using a Möllenstedt electron biprism — a charged wire that acts as the electron equivalent of Young's double slit — Tonomura and colleagues at Hitachi recorded the arrival of individual electrons on a detector. The early frames show only scattered dots, apparently random. As more electrons accumulate, the dots build into the characteristic interference fringes — *despite* each electron arriving discretely and singly, with no chance of "interfering with" any other electron present at the same time. The result is the most direct visual demonstration that wave-particle duality is a property of single quantum objects, not an artifact of many-particle ensembles. Voted "the most beautiful experiment in physics" in a 2002 *Physics World* poll.
Formulation
Electron source (low intensity, ~10 electrons/sec); biprism (acts as double slit); detector. Each electron arrives as a single dot. Accumulation: dots arrange into interference fringes over ~28 minutes / ~70,000 electrons. Each electron is interfering with itself.
Dimensions Engaged
Matter
Direct visual demonstration that wave-particle duality is intrinsic to individual quanta.
Observer
Engages Observer · Knowledge Extent: the interference pattern is a statistical result accessible only by accumulating many single-particle events.
Responses — How Schools Engage
Affirms / takes the bait 5
A definitive image of wave-particle duality: each electron is irreducibly both a localised arrival and a wavefront whose amplitude determines arrival statistics.
A canonical demonstration of quantum non-classicality in a single-particle regime. The result eliminates classical particle and classical wave readings simultaneously.
Quantum mechanics describes real single particles whose behaviour cannot be captured by classical descriptions. The image is decisive realist evidence.
The interference pattern is structural: a relation between amplitudes from different paths, manifested only statistically. Pure structural physics.
Operationally exemplary: the build-up is directly observable; the wave-particle relation is given empirical content by the experiment, not by metaphysical fiat.
Reframes the question 1
Everettian: each electron lands somewhere on each branch; the build-up pattern reflects the Born-rule weighting of branches. No collapse needed.
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Further reading
- Tonomura et al. (1989), op. cit.
- Tonomura, *Electron Holography* (1999)
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