  In close analogy to quantum electrodynamics, we derive a quantum field theory
of Josephson plasma waves (JPWs) in layered superconductors (LSCs), which
describes two types of interacting JPW bosonic quanta: one massive and the
other almost-massless. We also calculate the amplitude of their decay and
scattering. We propose a mechanism of enhancement of macroscopic quantum
tunneling (MQT) in stacks of intrinsic Josephson-junctions (SIJJs). Due to the
long-range interactions between many junctions in the LSCs, the calculated MQT
escape rate $\Gamma$ has a very nonlinear dependence on the number of junctions
in the stack. This allows to quantitatively describe striking recent
experiments in Bi2212 stacks.
