**math.OA Operator Algebras**

 - (In "Nature") Operator algebras, and, more broadly, operator theory, appear in mathematical models for quantum phenomena. 
 - (In Engineering) Completely positive maps are [used][1] in quantum information theory. There are also many [connections between operator algebras and wavelets][2], which is useful in electrical engineering.


  [1]: https://en.wikipedia.org/wiki/Quantum_channel
  [2]: https://books.google.com/books?id=CKVXzNo6KwwC