The flow of matter, from macroscopic water currents to the microscopic flow of electric charge, underpins much of the infrastructure of modern times. In the search for breakthroughs in energy efficiency, data storage capacity, and processing speed, scientists search for ways in which to control the flow of quantum aspects of matter such as the "spin" of an electron—its magnetic moment—or its "valley state," a novel quantum aspect of matter found in many two dimensional materials.