TUNNELING OF A QUANTUM BREATHER IN A ONE-DIMENSIONAL CHAIN

We investigate a chain of particles (bonds) with harmonic interbond an d anharmonic intrabond interactions. In the classical limit we conside r a breather solution that is strongly localized (essentially a single -site excitation). For the quantum case we study tunneling of this exc itation to epsilon. neighboring site. In that case we neglect the anha rmonicity except for the two sites between which the tunneling occurs. Within this model the breather tunneling reduces to the tunneling in a dimer coupled to two adjacent harmonic chains. Application of Feynma n's path instanton technique yields the tunneling splitting Delta E.Fo r the isolated dimer we reproduce the exponential factor for the split ting Delta E-(0), obtained earlier by a perturbative approach. Assumin g the frequency omega of the breather to be much larger than the inver se instanton width we use an adiabatic approximation to derive Delta E for the dimer coupled to the harmonic chains. We find that Delta E ca n be obtained from Delta E-(0) just by scaling the Planck constant. We argue that independent of the density of states tunneling can never b e suppressed, if omega is large enough.