Persistent Currents in Mesoscopic Loops and Networks

Authors: IGOR O. KULIK

Abstract: The paper describes persistent (also termed ``permanent", or ``non-decaying") currents in mesoscopic metallic and macromolecular rings, cylinders and networks. The current arises as a response of system to Aharonov-Bohm flux threading the conducting loop and does not require external voltage to support the current. Magnitude of the current is periodic function of magnetic flux with a period of normal-metal flux quantum \Phi_0 = hc/e. Spontaneous persistent currents arise in regular macromolecular structure without the Aharonov-Bohm flux provided the azimuthal periodicity of the ring is insured by strong coupling to periodic background (a ``substrate"), otherwise the system will undergo the Peierls transition arrested at certain flux value smaller than \Phi_0. Extremely small (nanoscopic, macromolecular) loop with three localization sites at flux \Phi = \Phi_0/2 develops a \Lambda-shaped energy configuration suitable to serve as a qubit, as well as at the same time as a ``qugate" (quantum logic gate) supporting full set of quantum transitions required for universal quantum computation. The difference of the Aharonov-Bohm qubit from another suggested condensed-matter quantum computational tools is in the radiation free couplings in a qubit supporting the scalable, long-lived quantum computation.

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