Danish-born computer scientists and software engineers have taken leading roles in some of the world's programming languages: Anders Hejlsberg (Turbo Pascal, Delphi, C#); Rasmus Lerdorf (PHP); Bjarne Stroustrup (C++); David Heinemeier Hansson (Ruby on Rails); Lars Bak, a pioneer in virtual machines (V8, Java VM, Dart). Physicist Lene Vestergaard Hau is the first person to stop light, leading to advances in quantum computing, nanoscale engineering, and linear optics.