  We present numerical and analytical studies of a quantum computer proposed by
the Yamamoto group in Phys. Rev. Lett. 89, 017901 (2002). The stable and
quantum chaos regimes in the quantum computer hardware are identified as a
function of magnetic field gradient and dipole-dipole couplings between qubits
on a square lattice. It is shown that a strong magnetic field gradient leads to
suppression of quantum chaos.
