You can create an index, however, there are a lot of conditions that need to be satisfied before you can do that. Some of them are:
1. Underlying table and view must both be created with ANSI_NULLS and ANSI_PADDING on.
2. View has to be created with schemabinding.
3. You cannot use the keyword "distinct" in the view definition. You can use a group by clause with a Count_big operator(Wont accept a count operator).
4. The first index on the view has to be a clustered, unique index so it can materialize the view.