Traditionally quantum tunneling in a static SQUID is studied on the basis of
a classical trajectory in imaginary time under a two-dimensional potential
barrier. The trajectory connects a potential well and an outer region crossing
their borders in perpendicular directions. In contrast to that main-path
mechanism, a wide set of trajectories with components tangent to the border of
the well can constitute an alternative mechanism of multi-path tunneling. The
phenomenon is essentially non-one-dimensional. Continuously distributed paths
under the barrier result in enhancement of tunneling probability. A type of
tunneling mechanism (main-path or multi-path) depends on character of a state
in the potential well prior to tunneling.Comment: 9 pages, 8 figure
