Electron parity controls charge addition to a superconducting island

What changed

Lafarge, Joyez and colleagues used Coulomb-blockade electrometry to measure how electron-number parity changes the free energy of a small superconducting island. In one device, unequal widths of successive charge steps gave the temperature-dependent cost of an unpaired electron. A later device with a larger superconducting gap relative to its charging energy showed charge steps of two electrons at low temperature and field; increasing either restored intermediate or single-electron steps.

Scientific scope

Lafarge, Joyez and colleagues used Coulomb-blockade electrometry to measure how electron-number parity changes the free energy of a small superconducting island. In one device, unequal widths of successive charge steps gave the temperature-dependent cost of an unpaired electron. A later device with a larger superconducting gap relative to its charging energy showed charge steps of two electrons at low temperature and field; increasing either restored intermediate or single-electron steps. The two experiments used different samples and charging regimes. Two-electron periodicity alone does not establish two-electron charge quantization. The inference relies on calibrated mean-charge measurements, weak tunnelling and equilibrium models; low-temperature deviations and a fitted mean-free-path discrepancy retain their source-level uncertainty. These observations do not demonstrate an operating Cooper-pair pump, a coherent qubit or universal parity protection. The cited manuscripts are reproduced in a 1993 thesis; their wording may differ from the journal versions.

Evidence

The linked original works support the scoped statement and contribution attribution. WRS has not independently replayed experiments or reconstructed a full mathematical proof. The two experiments used different samples and charging regimes. Two-electron periodicity alone does not establish two-electron charge quantization. The inference relies on calibrated mean-charge measurements, weak tunnelling and equilibrium models; low-temperature deviations and a fitted mean-free-path discrepancy retain their source-level uncertainty. These observations do not demonstrate an operating Cooper-pair pump, a coherent qubit or universal parity protection. The cited manuscripts are reproduced in a 1993 thesis; their wording may differ from the journal versions.

Contributors

• The named authors in the research record · SCIENCE: These are the listed authors of the cited contribution sources. Paper authorship does not quantify individual effort. An incomplete list is explicitly marked; same names are not automatically merged.

• Measurement of the even-odd free-energy difference of an isolated superconductor; Two-electron quantization of the charge on a superconductor — complete author manuscripts in Lafarge thesis

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