  In [Phys. Rev. Lett. 95, 080502 (2005)], Zheng proposed a scheme for
implementing a conditional phase shift via adiabatic passages. The author
claims that the gate is "neither of dynamical nor geometric origin" on the
grounds that the Hamiltonian does not follow a cyclic change. He further argues
that "in comparison with the adiabatic geometric gates, the nontrivial cyclic
loop is unnecessary, and thus the errors in obtaining the required solid angle
are avoided, which makes this new kind of phase gates superior to the geometric
gates." In this Comment, we point out that geometric operations, including
adiabatic holonomies, can be induced by noncyclic Hamiltonians, and show that
Zheng's gate is geometric. We also argue that the nontrivial loop responsible
for the phase shift is there, and it requires the same precision as in any
adiabatic geometric gate.
