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Researchers measured quasiparticles in a fractional quantum Hall state with a charge consistent with one quarter of an electron’s charge. They did not split an electron: the result concerns collective excitations in a quantum system, inferred from electrical noise in two separate experiments.
What the experiment measured
The team studied the ν = 1/2 fractional quantum Hall state in a 70-nanometre-wide gallium arsenide (GaAs) layer, as described by EPFL in its 2026 account. In this state, the relevant carriers are quasiparticles—excitations of the collective quantum system—not pieces of an individual electron.
To ask “what charge do its quasiparticles carry?”, researchers used an etched quantum point contact: a narrow constriction where quasiparticles can be partially scattered. They inferred charge from shot noise, the electrical fluctuations produced as carriers pass through the constriction. The team first checked the method against quantum Hall states with known charges of one electron and two-thirds of an electron. EPFL’s report describes the experimental setup and measurements.
Two experiments produced estimates consistent with e/4
EPFL and Weizmann researchers measured two nearly identical devices in separate laboratory setups. EPFL’s 2026 account reports the following fitted quasiparticle charges:
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| Device and measurement site | Fitted charge estimate | How to read it |
|---|---|---|
| First device, EPFL | 0.250 ± 0.013 times the electron charge | Consistent with e/4 |
| Second device, Weizmann | 0.249 ± 0.018 times the electron charge | Consistent with e/4 |
The uncertainties matter: these are experimental estimates, not exact values. Their agreement across the two devices is consistent with quasiparticles carrying one quarter of the electron charge. The account identifies two devices; it does not establish a larger sample or a population-wide statistic.
Why fractional charge does not mean a split electron
In a fractional quantum Hall system, many electrons in a strong magnetic field form a collective state. Its excitations can behave as if they carry a fraction of the electron’s charge. The measured fraction characterizes those excitations in that state; it does not mean an electron was physically cut into smaller, free-standing pieces.
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What the result says—and does not say—about anyons
Even-denominator quantum Hall states such as ν = 1/2 have drawn interest because some theories predict that they may host non-Abelian anyons. Such particles are of interest partly because their exchange behavior could, in principle, support approaches to topological quantum computing.
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This experiment measured quasiparticle charge. That measurement alone does not establish non-Abelian exchange statistics, demonstrate a working quantum computer, or show fault-tolerant computation. The link to quantum computing is a potential motivation for studying the state, not an outcome of this charge measurement.
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The results are reported in Tomer Alkalai et al., “Observation of e/4 charge at ν = 1/2 in GaAs,” published in Physical Review Letters on 22 September 2026, according to EPFL’s listing. View the paper’s DOI record.
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