That is a new paper by Chiara Franzoni, Giuseppe Scellato and Paula Stephan, and the abstract is this:
Migrant scientists outperform domestic scientists. The result persists after instrumenting migration for reasons of work or study with migration in childhood to minimize the effect of selection. The results are consistent with theories of knowledge recombination and specialty matching.
By the way, over sixty percent of the scientists and engineers of Silicon Valley were born outside of the United States. By the way, here is a new Swiss paper (pdf) on attitudes toward immigrant foreigners.