A quantum singularity is min-black hole that connects different worlds and parallel dimensions. People in different universes can travel between the universes through a quantum singularity.
There are two known ways to open a quantum singularity. The first is to fire a phased polaron cannon simultaneously from both worlds, from the same location and into the same black hole.
As only a single phased polaron cannon exists in the world, this is generally difficult. The second way is to create a Quantum Singularity Machine, which is designed to duplicate the effects of the first way.