A mechanism is provided for ratcheting a double strand molecule. The double strand molecule is driven into a Y-channel of a membrane by a first voltage pulse. The Y-channel includes a stem and branches, and the branches are connected to the stem at a junction. The double strand molecule is slowed at the junction of the Y-channel based on the first voltage pulse being weaker than a force required to break a base pair of the double strand molecule. The double strand molecule is split into a first single strand and a second single strand by driving the double strand molecule into the junction of the Y-channel at a second voltage pulse.