QUROPE Quantum Information Processing and Communication in Europe

The inclusion of charging and spin-exchange interactions within the Universal Hamiltonian description of
quantum dots is challenging as it leads to a non-Abelian action. Here we present an exact analytical solution
of the probem, in particular, in the vicinity of the Stoner instabilty point. We calculate several observables,
including the tunneling density of states (TDOS) and the spin susceptibility. Near the instability point the
TDOS exhibits a non-monotonous behavior as function of the tunneling energy, even at temperatures higher
than the exchange energy. Our approach is generalizable to a broad set of observables, including the a.c. sus-
ceptibility and the absorption spectrum for anisotropic spin interaction. Our results could be tested in nearly
ferromagnetic materials.