Bit of an aside, but China are probably the world leaders in quantum cryptography [...snip...]
You are describing something on the other end of the equation, that is something that would serve as a countermeasure to QC cracking encryption.
I don't know if the Chinese scientists came up with this technology/ability on their own, but I do know the Chinese have a long history of stealing technology from the West. If a western company working for a Western government originally created this technology, it may not be publicly known.
I also believe that QC and QC proof encryption are two separate and distinct technologies. I don't believe having the ability to do one does not necessarily make it easier to obtain the technology to have the ability to do the other.
You are absolutely correct that QC and QC-proof encryption are entirely separate areas. QC-proof encryption is
post-quantum cryptography, which aims to devise and employ cryptographic techniques that are secure because they negate any quantum advantage. Approaches like AES256, where the best quantum attack (Grover algorithm) gives QCs only a very minor advantage. P-QC is classical; in this defence there is no dependency on quantum hardware.
You are also correct that in that post I was describing a different countermeasure,
quantum cryptography, which involves employing quantum processes to achieve security. It does irritate me that post-quantum cryptography and quantum cryptography have such similar names, when they are fundamentally different things.
I do think that post-quantum cryptography is what we need in the near future to defend against QC attack. However longer-term I'm not so sure. I believe that post-quantum cryptography can never be as secure as a system that relies on the basic 'unhackability' of an entangled quantum system, such as that being developed by China's QUESS and Micius.
As for whether China stole the technology, I'm not so sure. It's difficult to deny that they are ahead of the rest of the world in quantum cryptography, so whatever base they started from they have advanced by themselves. All new tech, all new science, is built on the successes of predecessors.
Last year the US
downed an Iranian drone near one of it's warships with technology that disabled the drone. I don't know the specifics of what the US ship did, nor the underlying technology. Imagine a country could prevent another country's war planes from taking off (or from continuing to fly), or could send a signal to change the course of another country's missiles that have been launched.
That's obviously impressive and potentially concerning. We do need to remember though that the advantages of quantum computers are limited to very specific areas, such as prime factorisation. In other areas they are no better than normal classical computers. Certainly the ability of QCs to break asymmetric cryptography could wreak havoc, but P-QC does offer solid defences, so - and I may be being naive - I think that the abilities of QCs are sometimes overstated, and critical systems can be protected, it's just a case of getting that protection implemented in time.