Minimize the following function:

$ f(V) = || V \otimes V - U_1 \otimes U_2 ||$

where $U_1, U_2 \in SU(n)$ are fixed and we minimize over all $V \in SU(n)$. The norm is from the trace inner product.

The minimum value of $f$ and the $V$ which minimizes it are both important.

Cross posted on mse.