Not a cryptography expert but did a little digging. My understanding is that quantum computers (QCs) are a different type of computer that can perform new types of computations, not some super computer that does the same types of computations faster.

As discovered by Peter Shor in 1994, quantum computers will be able to calculate our private keys from our public keys. Has to do with the prime numbers we use in the crypto math. But QCs won’t be able to mine blocks quicker or reorg the chain. Hashes are mostly safe.

Bitcoin network will need to fork in a new type of key and signing algorithm so users can protect their funds, with enough time for all existing holders to transfer funds to new keys.

IMO notable concerns include:

1. What do we do with old or lost coins (like satoshi’s). Do we make them unspendable or let the first QC that can crack those keys become super wealthy?

2. Quantum safe crypto signatures are much larger signatures than our current sigs. When we upgrade the signatures we won’t be able to fit as many transactions in a block. Do we increase the block size to fit the same amount of txs or essentially accept a block size reduction?

3. How far away is the threat? When should we act? 5 years? 10? 50? Some argue we have plenty of time to learn more and weigh our options, others feel we should act now. Haven’t seen anyone agree on this one.