Nexus claims to be
http://www.nexusearth.com/In addition to checks and balances in consensus and Trust Keys with Network recognized Reputation providing greater security and network stability, Nexus also has Quantum Computer Resistant Private Keys with 571-bit encryption (much more secure than Bitcoin). Meaning, Nexus serves the WORLD as the most secure cryptocurrency to date.
I also thought I heard someone from Heat talking about this but I'm not sure if Heat is (maybe)
it's false, that quantum can break sha 256, they are spreading misinformation in fct it's not sha256 which is in danger of quantum when they will be available, but it's a round of hash to have the private key, i think it was called ECDSA but i maybe wrong, this is vulnerable, and if nexus is using this for their private key they will be vulnerable also
Nexus is using 571bit priv keys, still as i believe it is using elliptic curve cryptography but having a greater bit length means it would require much more qbits to crack than bitcoin for example. Theres no such thing as quantum proof only quantum resistant cryptography.
Also regarding the argument that bitcoin can simply fork to a new algo, no one can even agree on how to solve the scaling issue with bitcoin i wouldn't bet on a hard fork to change anything in bitcoin being adopted in a short span of time. The time in which it took to reach consensus would leave any priv key used more than once vulnerable.