Photolithography "printing with light" is an invention of the 20th century in which engineers selectively expose a photo-reactive "photoresist" with patterns of light; wherever the resist is exposed it can be chemically etched away (positive resists), or vice versa (negative resists). Photolithography is what makes it possible for engineers to design tiny planar electronic structures hundreds of times smaller than the width of a human hair, giving rise to computer microchips. Here we observe the state of the art in the design of these tiny electronic structures, which taper a thin layer of metal on silicon into narrow bottlenecks, creating channels for liquid helium to fill. Electrons floating on helium in the channel should pass through each bottleneck one at a time -- much as a subway turnstile allows only one person to pass through at a time.