  In this paper we study electron interference in nanotube loops. The
conductance as a function of the applied voltage is shown to oscillate due to
interference between electron beams traversing the loop in two opposite
directions, with slightly different velocities. The period of these
oscillations with respect to the gate voltage, as well as the temperatures
required for the effect to appear, are shown to be much larger than those of
the related Fabry-Perot interference. This effect is analogous to the Sagnac
effect in light interferometers. We calculate the effect of interactions on the
period of the oscillations, and show that even though interactions destroy much
of the near-degeneracy of velocities in the symmetric spin channel, the slow
interference effects survive.
