In a $d$ dimensional vector space defined over $\mathbb{C}$, how do I calculate the largest number $N(\epsilon, d)$ of vectors $\{V_i\}$ which satisfies the following properties. Here $\epsilon$ is smaller but finite compared to 1.

$$\langle V_i, V_i\rangle = 1$$

$$|\langle V_i, V_j\rangle| \leq \epsilon, i \neq j$$

Some examples are as follows.

$N(0, d)$ = d

$N\left(\frac{1}{2}, 2\right)$ = 3

$N\left(\frac{1}{\sqrt{2}}, 2\right) = 6$

How do I obtain any general formula for $N(\epsilon, d)$. Even an approximate form for $N(\epsilon, d)$ in the large $d$ and small $\epsilon$ ($\epsilon \ll 1$) limit works fine for me.