SPONTANEOUS AND PERSISTENT CURRENTS IN MESOSCOPIC AHARONOV - BOHM LOOPS: STATIC PROPERTIES AND COHERENT DYNAMIC BEHAVIOR IN CROSSED ELECTRIC AND MAGNETIC FIELDS
Kulik I.O.

Received: June 8, 2004

PACS: 73.23.Ra, 73.63.-b, 03.65.Vf, 03.67.Lx

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Mesoscopic or macromolecular conducting rings with a fixed number of electrons are shown to support persistent currents due to the Aharonov - Bohm flux, and the «spontaneous» persistent currents without the flux when structural transformation in the ring is blocked by strong coupling to the externally azimuthal-symmetric environment. In the free-standing macromolecular ring, symmetry breaking removes the azimuthal periodicity, which is further restored at the increasing field, however. The dynamics of the Aharonov - Bohm loop in crossed electric and magnetic fields is investigated within the tight-binding approximation; we show that transitions between discrete quantum states occur when static voltage pulses of prescribed duration are applied to the loop. In particular, the three-site ring with one or three electrons is an interesting quantum system that can serve as a qubit (quantum bit of information) and a qugate (quantum logical gate) because in the presence of an externally applied static electric field perpendicular to a magnetic field, the macromolecular ring switches between degenerate ground states mimicking the NOT and Hadamard gates of quantum computers.