Coulomb-related symmetry in laser-induced tunneling ionization of atoms and molecules

In tunneling ionization of an atom induced by a strong laser field, the system initially located in its ground state will be excited. The time-dependent wave function of the excited system includes bound- and continuum-eigenstate components of the field-free Hamiltonian. Here, we study the relation between the average kinetic energy and potential energy of the bound wave packet composed of coherent superposition of higher bound eigenstates. Our simulations show that around the peak time of the laser field at which the tunneling effect is strong, the bound wave packet still approximately agrees with the virial theorem, which reflects the Coulomb-related spatial symmetry of the system. Our results indicate that during the laser-induced exciting process, the system tends to keep its symmetry before ionization. This observation also holds for small molecules. It gives suggestions on analytically constructing Coulomb-included strong-field models.