Monopoles, dubbed dowsons, are point singularities of the unitary complex order parameter exp(ij) characterizing the so-called dowser texture in a thin nematic layer with homeotropic boundary conditions. Using setups called dowsons colliders, pairs of dowsons are generated and set into motion on counter-rotating trajectories leading to collisions. In a first approximation, the velocity of dowsons is orthogonal and proportional to the local phase gradient. The outcome of collisions depends on the distance of dowsons’ trajectories in terms of the phase: for dj < p, a collision of a pair of dowsons leads to their annihilation while for dj > p the colliding dowsons are passing by. This rule is valid only for quasi-static stationary wound up phase fields and can be easily broken by application of a Poiseuille flow in an appropriate direction (see Figure).
Pairs of disclinations are generated in a reproducible manner by the isotropic-nematic transition in twisted nematic cells submitted to magnetic fields of appropriate geometries. Their collision, driven by an electric field, leads to a rewiring process that can be fully controlled by means of the magnetic and electric fields.