The bound pairs of electrons, known as Cooper pairs, that are responsible for carrying current in superconductors can unbind if they are hit with high-frequency phonons or photons. This unbinding is detrimental for superconductivity but has been leveraged to make single-particle detectors. Most of these detectors, however, require calibration or modeling for researchers to be able to infer from their signals the exact number of particles that hit the detector. Now, Elsa Mannila of Aalto University, Finland, and her colleagues have demonstrated a detector that can directly measure from an electrical current the number of broken Cooper pairs and thus particles that were absorbed [1].
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