A good QC owner would use it as follows:


The aim is to generate a win-win situation for the QC owner and the Bitcoin community. Satoshi knew that one day QC will move the "lost" coins otherwise he could transfer them to QC resistant unused P2PKH addresses. And his early mined "lost" coins have the most volume, but they are distributed on thousands of addresses that nobody can get them at once (number of transactions and block size). We will know that someone owns a QC if these "lost" coins start to being moved and can change to QC resistant addresses.


That would end the Bitcoin project.


Btw.: Satoshi has enough other Bitcoins than the known "lost" coins. He mined on several machines but we only know his "lost" coins.  (our opinion)

1+ million Bitcoins, the other "lost" coins are QC resistant



We want to make Bitcoin better and stronger.



We don't think that QC development will happen step by step. Our expectation is that someone will find a QC technology, that allows "far beyond expectations" numbers of qubits, that will allow this QC to get all private keys immediately.
We think that such a QC will surprise the Bitcoin community and only thereafter we will upgrade to a quantum resistant Bitcoin network. We hope that the user of such a QC to get the private keys, knows exactly how Bitcoin works and allows the owners to transfer their coins to the new QC resistant addresses. It would be a win-win game: the QC user would get the "lost" coins, the Bitcoin owners could transfer their coins to QC resistant addresses, the Bitcoin ecosystem wouldn't be affected, we would have a stronger Bitcoin network. How would a QC user act: starting with the oldest "lost" coins and moving them, so that the Bitcoin community can realize that someone is moving the "lost" coins (e.g. a special posting board here on bitcointalk) but gives the owners the possibility to transfer their coins to other addresses. In the meantime we will have a very quick "quantum resistance upgrade". And it will continue like DannyHamilton described it:
but stronger

The legacy P2PK addresses, even unspent with no outgoing transactions, are not quantum resistant. Satoshi knows it, but he has more than 1 million Bitcoins on P2PK addresses.
That's the reason why one should transfer the Bitcoins from old P2PK addresses or used addresses to new unused addresses to make them quantum resistant.

https://www.digicert.com/resources/industry-report/2019-Post-Quantum-Crypto-Survey.pdf
Slightly more than half (55 percent) say quantum computing is a “somewhat” to “extremely” large threat today,
with 71 percent saying it will be a “somewhat” to “extremely” large threat in the future.

Yes, not predictable. It could even happen tomorrow.

We are getting closer:

The boss of Google has warned that quantum computers will be able to break encryption within as little as five years, signalling the growing threat to privacy such technological advances.
https://www.telegraph.co.uk/technology/2020/01/22/googles-sundar-pichai-quantum-computing-could-end-encryption/
"In a five to ten year time frame, quantum computing will break encryption as we know it today."

@ satoshi: Thank you for that amazing and incredible way of distribution of Bitcoins. You support and reward the best technology.

How the Crypto World Is Preparing for Quantum Computing, Explained
https://cointelegraph.com/explained/how-the-crypto-world-is-preparing-for-quantum-computing-explained

"While present-day quantum computers cannot break blockchains and their underlying cryptography, larger ones on the horizon are a threat, indeed, and need to be prepared for."

@ developers: When will we implement quantum computer resistant addresses?
@ satoshi: You filled the blockchain with your early mined coins and the quantum transformation will be very interesting. Who will get the most coins?

Quantum computing boost for IBM but Bitcoin stays safe https://decrypt.co/16211/quantum-computing-boost-for-ibm-but-bitcoin-stays-safe
IBM has doubled the power of its quantum computer but Bitcoin's encryption is still far from being broken.
"IBM has doubled the power of its quantum computer. At yesterday's CES 2020 conference, the company announced it had successfully achieved a Quantum Volume of 32 using its 28-qubit quantum computer known as Raleigh."
"As a network built entirely around cryptographically secured transactions, it stands to reason that a sufficiently powerful quantum computer could eventually crack the encryption used to generate Bitcoin private keys. However, according to a June 2017 paper by Martin Roetteler and several co-authors, such as a machine would need to command approximately 2,500 qubits of processing power to break the 256-bit encryption used by Bitcoin."

A Quantum Computing Future Is Unlikely https://www.govtech.com/products/A-Quantum-Computing-Future-Is-Unlikely-Due-to-Random-Hardware-Errors.html
Google claims quantum supremacy – IBM says not so fast. One researcher explains why he doesn't see quantum computers outpacing classical computers any time soon ... and maybe not ever.
"As someone who has worked on quantum computing for many years, I believe that due to the inevitability of random errors in the hardware, useful quantum computers are unlikely to ever be built."