Poseidon is a super elegant hash function, part 2:

Even an optimized STARK arithmetization can fit into a single screenshot

While I love to share your optimism most times, Quantum computers can use Grover's algorithm to perform a square root speedup for brute-force attacks on hash functions. This would reduce the effective security of the hash function from \(2^n\) to \(2^{n/2}\). For Poseidon, this means doubling the security parameter to maintain the same level of security. Also construction of Poseidon involves specific arithmetic operations over prime fields. Quantum algorithms that excel at solving problems in these fields could potentially weaken Poseidon's security. While all is theoretically yet, bullet proof tests can only be done as soon we will service fully at the quantum era. - Quantum futura incerta, praesens fortis sit.