Flip-Flopping Fractional Flux Quanta

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Science  09 Jun 2006:
Vol. 312, Issue 5779, pp. 1495-1497
DOI: 10.1126/science.1126041

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The d-wave pairing symmetry in high–critical temperature superconductors makes it possible to realize superconducting rings with built-in π phase shifts. Such rings have a twofold degenerate ground state that is characterized by the spontaneous generation of fractional magnetic flux quanta with either up or down polarity. We have incorporated π phase–biased superconducting rings in a logic circuit, a flip-flop, in which the fractional flux polarity is controllably toggled by applying single flux quantum pulses at the input channel. The integration of p rings into conventional rapid single flux quantum logic as natural two-state devices should alleviate the need for bias current lines, improve device symmetry, and enhance the operation margins.

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