[shalg]

There are exactly 2 reasons we might want quantum networks.

1. 100% secure communication channels (even better we can detect any attempt at eavesdropping and whatever information is captured will be useless to the eavesdropper)

2. Building larger quantum computers. A high fidelity quantum network would allow you to compute simultaneously with multiple quantum chips by interfacing them.

The thing that makes quantum networking different from regular networking is that you have to be very careful to not disturb the state of the photons you are sending down the fiber optics.

Im currently doing my PhD building quantum networking devices so im a bit biased but I think it’s pretty cool :).

Now does it matter I’m not sure. Reason 1 isn’t really that useful because encryption is very secure. However if quantum computers start to scale up and some encryption methods get obsoleted this could be nice. Also having encryption that is provably secure would be nice regardless.

Reason 2 at the moment seems like the only path to building large scale quantum computing. Think a datacenter with many networked quantum chips.

[nativeit]

> 100% secure communication channels (even better we can detect any attempt at eavesdropping and whatever information is captured will be useless to the eavesdropper) chips. A few follow up questions:

1. What is it about quantum computers that can guarantee 100% secure communication channels?

2. If the communications are 100% secure, why are we worried about eavesdropping?

3. If it can detect eavesdropping, why do we need to concern ourselves with the information they might see/hear? Just respond to the detection.

4. What is it about quantum computing that would make an eavesdroppers’ overheard information useless to them, without also obviating said information to the intended recipients?

This is where the language used to discuss this topic turns into word salad for me. None of the things you said necessarily follow from the things that were said before them, but rather just levied as accepted fact.

[SAI_Peregrinus]

1. Nothing. Quantum Key Distribution is what they're talking about, and it still requires P!=NP because there's a classical cryptographic step involved (several, actually). It just allows you to exchange symmetric keys with a party you've used classical cryptography to authenticate, it's vulnerable to MITM attacks otherwise. So you're dependent on classical signatures and PKI to authenticate the endpoints. And you're exchanging classical symmetric keys, so still dependent on the security of classical encryption like AES-GCM.

2. Because they're not 100% secure. Only the key exchange step with an authenticated endpoint is 100% secure.

3. Eavesdropping acts like a denial of service and breaks all communications on the channel.

4. It makes the information useless to everyone, both the eavesdropper and the recipients. Attempting to eavesdrop on a QKD channel randomizes the transmitted data. It's a DOS attack. The easier DOS attack is to break the fiber-optic cable transmitting the light pulses, since every endpoint needs a dedicated fiber to connect to every other endpoint.

[staunton]

> Only the key exchange step with an authenticated endpoint is 100% secure.

It's 100% secure in theory, assuming a model of the hardware (which is impossible to verify even if you could build it to "perfectly" satisfy all model assumptions, which of course you also can't).

[SAI_Peregrinus]

Yeah, the key exchange portion is secure. The resulting shared secret in RAM, on the other hand, is only as secure as the computer it's on. The moment you're out of the quantum realm by measuring the exchanged quanta, you lose the 100% security guarantee of the quantum portion of the key exchange. The Q part of QKD is actually secure, it's just that it's also useless and QKD as a whole exists mostly to fleece investors. It's a nerdy party trick, not a serious security mechanism.

[staunton]

There is no such thing as a magical "quantum realm". Devices performing quantum state preparation or measurements are just devices. They aren't perfect and can never be made to "100%" satisfy any assumptions.

The Q part is secure in theory, assuming your devices satisfy a specific theoretical model. That's not a 100% guarantee. In fact, it's just the same kind of guarantee as we get for any other security system: "We carefully examined the system and it seems like it satisfies the assumptions of our theoretical model, thus promising security".

Not that this is a bad thing, it's just that "quantum" doesn't make anything "magically 100% secure". There's no such thing as "100% security".

[SAI_Peregrinus]

Yeah, I should have specified "the photon packet in the fiber" instead of generic "quantum", but there isn't always actually a photon packet even when light is the medium, and there isn't always a fiber, and just mashing it all up as "quantum" was faster. Any interference with the actual stuff that's doing the information exchange will cause the communication to fail, so that one part of the system can't be eavesdropped on passively.

[foota]

Sorry, but I think the way you're phrasing this implies a burden on them to explain well understood and widely accepted principles of quantum physics that you seem to be implying are pseudoscience.

This seems like a decent overview if you want to learn more: https://www.chalmers.se/en/centres/wacqt/discover-quantum-te....

[_heimdall]

From the source you linked

> According to the laws of quantum physics, it is impossible to measure or copy an unknown state of a quantum particle without noticeably changing it.

That alone is a very clear description of how quantum mechanics is pseudoscience. Its based entirely on an untestable principle. When the initial state can't be measured because doing so changes the state we are left entirely unable to run a controlled study on it. You must know Tue state before and after an intervention to reliably and accurately deduce what happened or to begin to understand why it happened.

This is the one miracle that we must grant to allow the rest of quantum research to become possible.

[immibis]

No, it's all well-defined science. There's known mathematics for how the operations you do affect the probability distribution of the answer. The initial state can be prepared. It can't be measured after it's been prepared, because that would ruin it. But so what - that happens all the time in science. Your comment is like saying chemistry is a pseudoscience because if we put a pH indicator strip in before doing a certain reaction to prove it's an acid, the contamination by the indicator chemical stops the reaction from working.

We can simulate a quantum computer using a normal computer (in exponential time). Simulations of tiny quantum computers agree with the experiments using tiny quantum computers. We can also simulate less-tiny (but still pretty small because it takes exponential time) quantum computers. But we haven't built an actual one of those yet. It seems they're really hard to build But also no fundamental reason is known why it should be impossible to build one. Shouldn't it just be the same as a tiny one, but bigger? The tiny ones were hard enough to build, so maybe it's just really hard and we need better techniques.

Perhaps it will turn out to be a failed branch of science that leads to no practical applications, but it's certainly real science, studying real things and making testable predictions (which are true so far). I suppose your next objection will be that since we only have tiny quantum computers, non-tiny problems are pseudoscience, but that's like saying particle physics was pseudoscience before we built the Large Hadron Collider.

Recently 3Blue1Brown made a video attempting to explain Grover's algorithm, which is one of the main applications of quantum computing, that also covers basic ideas of quantum computing and some common misconceptions - have you seen it yet? https://www.youtube.com/watch?v=RQWpF2Gb-gU and followup: https://www.youtube.com/watch?v=Dlsa9EBKDGI

[_heimdall]

You're describing a field based on simulations and predictions. That is interesting, but it isn't scientific as you aren't actually testing anything when you only run simulations.

A simulation is an interesting indicator for future scientific research, but it is never scientific research in and of itself.

[immibis]

When your predictions are testable and agree with reality you did science.

[nativeit]

I feel like most of your answer was just re-stating the question. I’m happy to admit that’s almost certainly a mix of my ignorance on the topic at hand, and I have been primed to view the discussions surrounding quantum computing with suspicion, but either way, that’s the way it reads to this layperson.

[thesz]

What is the difference between channel error or distortion and eavesdropping?

[staunton]

For eavesdropping, there is someone there who cares about what you're sending and is successfully learning things about it.

[thesz]

How can one quantumly differentiate between photon lost due to eavesdropping and photon lost due to some other error?

[staunton]

Other than by going around and finding the eavesdropper sitting somewhere, one cannot.

[chatmasta]

If studio execs have their way, Quantum DRM will be the killer use case…

[autoexec]

Jokes on them, we'll just end up creating and using quantum pirating systems or even the dreaded Quantum Analog Hole to evade it.