`Flat Phase' Loading of a Bose-Einstein Condensate into an Optical Lattice

It has been proposed that the adiabatic loading of a Bose-Einstein Condensate
(BEC) into an optical lattice via the Mott-insulator transition can be used to
initialize a quantum computer [D. Jaksch, {\it et al.}, Phys. Rev. Lett. {\bf
81}, 3108 (1998)]. The loading of a BEC into the lattice without causing band
excitation is readily achievable; however, unless one switches on an optical
lattice very slowly, the optical lattice causes a phase to accumulate across
the condensate. We show analytically and numerically that a cancellation of
this effect is possible by adjusting the harmonic trap force-constant of the
magnetic trap appropriately, thereby facilitating quick loading of an optical
lattice for quantum computing purposes. A simple analytical theory is developed
for a non-stationary BEC in a harmonic trap.