  We present a simple way to quantize the well-known Margulis expander map. The
result is a quantum expander which acts on discrete Wigner functions in the
same way the classical Margulis expander acts on probability distributions. The
quantum version shares all essential properties of the classical counterpart,
e.g., it has the same degree and spectrum. Unlike previous constructions of
quantum expanders, our method does not rely on non-Abelian harmonic analysis.
Analogues for continuous variable systems are mentioned. Indeed, the
construction seems one of the few instances where applications based on
discrete and continuous phase space methods can be developed in complete
analogy.
