Quantum key exchange (only one of the applications of "quantum internet") is completely orthogonal to post quantum encryption.
Quantum key exchange is a way to distribute keys, which will be used in some symmetric encryption scheme that runs on classical computers. That scheme has security that does not depend on any "difficulty" conjectures. It is "information theoretically perfect" modulo implementation bugs. (Assuming Schroedinger's equation is not wrong).
This does not require the creation of a quantum computer. Actually it is much easier and already done in labs.
Post quantum encryption is just the name for asymmetric encryption algorithms that run on classical computers and are difficult to break on both classical and quantum computers.
Even though quantum key exchange is an exciting application of "quantum internet", way more interesting would be its use for the establishment of globe spanning entangled states. This can be used for the creation of sensors that surpass the diffraction limit and other practical "science stuff".
> Quantum key exchange is a way to distribute keys, which will be used in some symmetric encryption scheme
The largest use of an asymmetrical cryptographic algorithm is key distribution, for use with a symmetric algorithm.
> That scheme has security that does not depend on any "difficulty" conjectures. It is "information theoretically perfect" modulo implementation bugs.
Up to this point, I've never seen any design of quantum encryption that provides any actual security. It's an abstract property of them that there should be one way to get physical security, just like it's a property of computing that there should be some good NP-hard problem one can base a cryptographic algorithm on. AFAIK, both are open problems.
I would argue that nothing in this sector is "production-ready".
For key exchange, SIKE looks promising (especially with the prospect of a non-interactive version).
For signatures, the SPHINCS variants are also promising. Gravity-SPHINCS is more intriguing to me than SPINCS+, but, they're both good forks of an already good design.
I don't like where this is going.
> In stage 1, users will start getting into the quantum game, in which a sender creates quantum states, typically for photons.
Okay, it's going exactly where I thought I was going!
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At the risk of falling victim to the Gell-Mann effect, I'm going to call bullshit on this article.
It's overwhelmingly likely that quantum cryptography will not be the next iteration of network security technology in the real world. Rather, the focus is on what's called post-quantum cryptography. Despite what you might think, these are not two points on a timeline.
Post-quantum cryptography refers to asymmetric cryptography features that are secure even in the presence of practical quantum computers. It's not a stage that exists after quantum cryptography. There's no "intermediate" stage in which we use quantum physics itself for encryption.
There will likely be a transition, wherein today's elliptic curve cryptosystems are used in addition to a post-quantum cryptosystem (e.g. ECDH + RLWE), until industry-wide confidence is gained in the security of the latter. I expect a lot of interesting attacks to be found in PQ algorithms during that time, and eventually we'll settle on constructions that are secure without pre-quantum cryptography.
Note: Symmetric cryptography is largely unaffected by quantum computers. You essentially halve the security levels (nitpick: which is an exponent, so you'll effectively be taking the square root of the possible values rather than just "halving it", which would just shave off one bit).
Quantum key distribution and other entangled photon madness? I doubt we'll see widespread deployment of this.
EDIT: I see this article isn't the author's first inaccurate foray into this topic. They might want to consult a cryptographer before publishing bunk science. https://www.scientificamerican.com/article/the-quantum-inter...