What you've illustrated is not a sparse table, its an Entity-Attribute-Value (EAV) table. Entity Framework does not support EAV modeling, and it's probably just as well as it can lead to major performance issues.
If your attributes are not dynamic then you can model your data in a more conventional manner and use Sparse Columns, though they have their own pros and cons.
Given the way that Entity Framework works, for anything but the most trivial of applications you can kiss 3rd Normal Form goodbye.