The possible effects of trans-Planckian physics on the Bohm quantum trajectories of scalar field in conformal inflation are investigated in the lattice Schroedinger picture. For the Corley-Jacobson type dispersion relation with quartic or sextic correction, there exists a transition in the evolution of the quantum trajectories from well before horizon exit to well after horizon exit, thus providing a mechanism for generating a small cosmological constant. We also evaluate the vacuum energy density due to fluctuations of the inflaton field and the corresponding cosmological constant. We find that during the inflation at the grand unification phase transition, the cosmological constant is dependent on the dispersion parameters and the cutoff scale, and equal to the square of the Hubble parameter approximately for the usual parameter choice.