Sensing a Small But Persistent Current

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Science  09 Oct 2009:
Vol. 326, Issue 5950, pp. 244-245
DOI: 10.1126/science.1180577

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The idea that a normal, nonsuperconducting metal ring can sustain a persistent current—one that flows forever without dissipating energy—seems preposterous. Metal wires have an electrical resistance, and currents passing through resistors dissipate energy. Besides, time-reversal symmetry should forbid a current choosing one direction over the other around the ring.