  We study the Bose-condensed ground states of bosons in a two-dimensional
optical lattice in the presence of frustration due to an effective vector
potential, for example, due to lattice rotation. We use a mapping to a large-S
frustrated magnet to study quantum fluctuations in the condensed state. Quantum
effects are introduced by considering a 1/S expansion around the classical
ground state. The large-S regime should be relevant to systems with many
particles per site. As the system approaches the Mott insulating state, the
hole density becomes small. Our large-S results show that, even when the system
is very dilute, the holes remain a (partially) condensed system. Moreover, the
superfluid density is comparable to the condensate density. In other words, the
large-S regime does not display an instability to noncondensed phases. However,
for cases with fewer than 1/3 flux quantum per lattice plaquette, we find that
the fractional condensate depletion increases as the system approaches the Mott
phase, giving rise to the possibility of a noncondensed state before the Mott
phase is reached for systems with smaller S.
