I am not a cryptographer myself so maybe here we are just discussing on a normal guy's level. As far I know, quantum computing really has the potential to successfully decrypt the private keys and therefore can be the biggest threat to Bitcoin. In the past few days, this topic got spread around because Google announced that they already have the technology at hand which many of us supposed  should still be years ahead. Now, there is that fear in the Bitcoin community on quantum computing and whether this can really be utilized against Bitcoin which can be its end. Nobody can really be sure if the quantum computing developed by Google can effectively be the one to stop Bitcoin. This can be the one we can only wait and watch. As the technology is on the hands of Google, I don't think they will be irresponsible to just use it indiscriminately as this will have many legal repercussions which the company will not want to go through. On the other hand, we have to remember that if there is a demand someone will eventually fill the shoes therefore we should be expecting developers to come up with ways to counteract the power of quantum computing to balance things out. And this can actually make things exciting.

I've written similar things in another topic before. Why everyone is looking at the negative. We are talking about a computer with a very large processor power. Can you imagine the peak that mining can reach?

Quantum computings biggest rumored ace against bitcoin is its ability to break a blockchain encryption and might expose private keys that could mess up everything in crypto world. But blockchain news keeps on assuring that released versions of quantum computing can't break blockchain. Although existing versions of quantum computing doesn't have the latter ability, crypto space should get ready for one that has the ability to decrypt blockchain. In case that such events occured, that might trigger the official downfall of bitcoin if not a single move to counter the threat will be done.

Quantum Computer that is large enough would be bad for bitcoin, as it could get private key from your public key. But If you use bitcoin as recommended and you do not re-use your addresses, your public key is not visible, and even a big QC cant get your private key.

So if you use bitcoin as you should, your coins would still be safe.

Creating a bigger QC gets exponentially harder as the size increases. That is why building a QC big enough will take a lot of time, if it can ever even be made.
Googles QC was build for single purpose only and it is tiny  compared to what would be needed for cracking bitcoin. And also the calculation it made was quite different. It "proved" that something can't be done. Did it really prove that or were they a little optimistic at google? It is much easier to prove calculation to be correct, when you get a concrete result form it  

Also. QC would be really really bad at mining because SHA256 algorithm is considered quantum safe. Probably your laptop would be faster at mining than a QC

The real threat a large QC poses to bitcoin is the addresses that have their public keys visible. ALL of the big exchanges  keep their coins in addresses that are re-used, with visible public keys. And those addresses have loads of bitcoins. The 4 biggest ones have more than 100000BTC in each of them. That is more than 400000BTC. And lets not forget the 1M coins in Satoshi's addresses.
If someone steals all of them, that would make havoc to the value of bitcoin

Why would everyone have migrated to using something else, if the BIG break comes unexpectedly. Do you really think  NSA or whoever would publish that they can break a popular encryption.
AND that is of course the reason they would not crack bitcoin, because they would want to keep their ability a secret

It could. But that's it. It just could. Theoretically anyway. And even if that time could come, blockchain itself would have improved immensely and would have made precautions regarding quantum computers. Just like in the source you gave, Canada has already made baby steps towards the prevention of such thing from happening.
Also bro, this has made the forum quite a few times now, you should just probably look it up here and check some of the posts out. or i can just post it here, as such
https://bt.irlbtc.com/view/5188910.0
https://bt.irlbtc.com/view/5186831.0

From the article that I went through it looks like a hard thing for quantum computer to kill bitcoin. Quantum Computer performs much faster than other computers that are highly powerful. Also in the article it is mentioned we're far away from breaking the bitcoin for various reasons.

Reference Link of the article : Could Google Be About To Break Bitcoin?

I could say from my knowledge that this is a serious issue and there is no solution that would not harm BTC value. first, BTC upgrades, but the coins on lost addresses don't migrate to quantum resistant addresses and stay vulnerable. Eventually BTC might get hacked. That would cause a market reaction.
second, You create a deadline within people will need to move their BTC to QR addresses. After the deadline the leftovers will be burned. The problem is that in that scenario, you don't know which coins are on lost addresses and which coins are from people who have not migrated yet for whatever kind of reason. Not everybody is part of "the community", some just glance at the price every now and then and don't follow technical development. Investing in BTC doesn't obligate you to have a bitcointalk account. And there is no preset condition that obligates you to keep up with the developments. So developers would not have the right to burn your coins if you don't migrate in time. It's a legal issue inside BTC community.

Theoretically possible, but I think that it's also possible to find a solution. Beyond that it's at the moment and in the nearly future very hard and expensive to get a quantum computer and besides that a quantum computer must be developed for the purpose of destroying bitcoin (to solve SHA256), with a normal quantum computer, you don't have the "instruments" to solve SHA256 you have to develop a special system for the quantum computer. In my opinion the effort is too big for most of the people. Furthermore, quantum computer's can also be used to attack other things like bitcoin nearly everything could be hacked, and there are some big banks for instance, which would be more profitable and easier to attack.