  We describe an ultrafast coherent control of the transient structural
distortion arising from nonlinear phononics in ErFeO$_3$. Using density
functional theory, we calculate the structural properties as input to an
anharmonic phonon model that describes the response of the system to a pulsed
optical excitation. We find that the trilinear coupling of two orthogonal
infrared-active phonons to a Raman-active phonon causes a transient distortion
of the lattice. The direction of the distortion is determined by the
polarization of the exciting light, suggesting a route to nonlinear phononic
lattice control and switching. Since the occurrence of the coupling is
determined by the symmetry of the system we propose that it is a universal
feature of orthorhombic and tetragonal perovskites.
