  We study quantum tunneling of a composite object, which has a dipole or
quadrupole moment coupled with quantized (photon or gravitational) radiation
field, through a {\delta} potential barrier. The dipole or quadrupole moment is
represented by an oscillator in the relative coordinate of two constituent
particles of the object. The center of mass degrees of freedom of the object is
not directly coupled with the radiation field. However, we show that, for the
object with the oscillator in the excited state, dissipation caused by the
radiation field can suppress its quantum tunneling rate in the center of mass
degrees of freedom. In addition, when the initial energy of its center of mass
motion is similar to that of the excited state of the oscillator, a spatial
superposition state of the object prepared by the barrier can decohere due to
the radiation field. The main purpose of this article is to investigate how two
different interplays (i) among the center of mass, the relative coordinate
degrees of freedom and the potential barrier, and (ii) between the relative
coordinate degrees of freedom and the radiation field, can affect the quantum
tunneling and the creation of the spatial superposition state of the object.
Our toy model can give insight into tests of quantum tunneling and quantum
superposition of atoms or molecules with its dipole or quadrupole moment
coupled with the radiation field.
