  For a proton in the infinite momentum frame, its wave function contains a
zero-momentum part (light-front zero-modes) originated from the modification of
the QCD vacuum in the presence of the valence quarks, exhibiting a light-front
long-range order in the quantum state. This ``non-travelling'' component of the
proton contributes to its fundamental properties, including the mass and spin,
as well as the naive-time-reversal-odd correlations between transverse momentum
and spin. The large momentum effective theory (LaMET) provides a theoretical
approach to study the physical properties of the proton's zero-mode
``condensate'' through lattice simulations.
