I am currently reading through Computational Quantum Entanglement paper and there is a following statement there in proof of Lemma 4.1
We then use that an $\eta$-net (this is an $\epsilon$-net with different parameter) on $n(\lambda)$-qubit unitaries for the normalized Frobenius norm has size $(\frac{1}{\eta})^{\Omega(2^{2n(\lambda)})}$
This statement is used without any reference, yet it is not clear for me how this lower bound was achieved. Any pointers or reference material would be highly appreciated.