Strong Tunneling in the Single-Electron Box

We study strong tunneling (i.e., transmission h/e²RT1) in the single-electron box with many transverse modes at zero temperature. We develop a new renormalization group method which includes all charge states and requires no initial or final energy cutoff. We determine the ground-state energy, the average charge, and the renormalized charging energy. The covered range for the coupling constant and the gate voltage is much increased in comparison to recent perturbative approaches, ``poor-man'' scaling methods, and quantum Monte Carlo simulations. We reach the regime where Coulomb blockade becomes practically unobservable.