Schwinger pair production via instantons in strong electric fields

In the space-dependent gauge, each mode of the Klein-Gordon equation in a strong electric field takes the form of a time-independent Schroedinger equation with a potential barrier. We propose that the single instanton and multi-instantons of quantum tunneling may be related with the single-pair and multipair production of bosons and the relative probability for the no-pair production is determined by the total tunneling probability via instantons. In the case of a static uniform electric field, the instanton interpretation recovers exactly the well-known pair-production rate for bosons and, when the Pauli blocking is taken into account, it gives the correct fermion production rate. The instanton is used to calculate the pair-production rate even in an inhomogeneous electric field. Furthermore, the instanton interpretation confirms the fact that bosons and fermions cannot be produced by a static magnetic field only