The Quantum Future of Sharing Secrets Might Be a Bit Underwhelming

The quantum internet is way more exciting than most anything at the front edge of communications. At the same time, it’s highly underwhelming.

That is, on the one hand, quantum encryption is the promise of totally secure, unhackable-by-definition transmission. But on the other, it’s just a different way of doing a variety of secret-sharing that’s been around as an idea since the 1800s. And it's the same sort of secret-sharing that internet privacy is currently based around: passing a secret code through a public place.

In fact, the quantum internet should be more or less indistinguishable from the internet you’re on at this very moment, at least once it reaches your personal day-to-day internet. And the odds are that you don’t give two shits about the specifics of present-day secrecy methods like hashing and the RSA algorithm, or possibly even the difference between “http” and “https” (though you should). The future won’t be much different as far as your personal internetting is concerned.

However, the back-end of the quantum internet will look quite a bit different. That will involve lasers, a brand new satellite network, and the utilization of some of the more baffling properties of the universe, e.g. quantum mechanics. A very quick refresher: using the properties of quantum entanglement or quantum superposition, it’s possible for two parties to be coupled in such a way that they’re part of the same system, and any change to one is reflected in the other, hence communication. The neat thing is that the fragility of a quantum system makes it so that any attempt at eavesdropping on the system will be immediately detected and the message can be trashed. Perfect security (with some asterisks).

A popular idea is that a quantum internet or general quantum communication implies instantaneous/faster-than-light communication. Technology Review has a post up right now detailing a preliminary quantum internet that’s been running at Los Alamos for two years already (or detailing a paper detailing it). It’s perfectly underwhelming in that the network is, a) really just a series of one-to-one communications sharing a central, conventionally hackable node (A to B, A to C, A to D, etc.) and, b) that the actual messages are being transmitted classically with only the secret keys being transmitted via quantum means (as expected).

A comment on the TR post sums up the popular notion of FTL communication, and the assumed popular disappointment:

If my understanding of quantum science is correct, transmission speed should be unaffected by distance, making radio for space communications effectively obsolete, and making current fiber and copper transcontinental connections obsolete as soon as fast, expensive, reliable quantum routers are available.

This is a common pop-sci misreading of quantum entanglement, the property of two things being coupled in a system over a long distance such that a change in one effects a change in the other at the same instant. It’s a very neat and real property, but it has the inconvenient catch that while there is an actual communication that happens in an instant, it’s not useful. The state-change is meaningful if and only if you have some other information about the system transmitted via the usual, relativity-obeying methods. The “message” you get is always in relation to some other information, sadly. You’re only receiving one part of a conditional “if A than B,” where A is totally useless without B. So, if you get A absent the entire conditional, whatever.

An answer on Cornell's "Ask an Astronomer" page has a useful example:

Say you agree to send out two beams of light to your two friends who live on opposite sides of the galaxy (you live in the middle). Ahead of time you tell them that if one of the beams of light is red the other will be blue. So you send the blue beam to your friend on one side and immediately she knows that your other friend is recieving a red beam at the same time. Aha! You say, my friends have now communicated at a speed faster than the speed of light and violated relativity, but no real information has been passed between them. You have told both of them at a normal sub-luminal speed about what you just did and that's all. (A way of proving there's no faster than light communication is that you could lie and send them both the same coloured beam of light and they would never know!).

While the quantum internet of the future might feel more mundane in reality, at the same time it's interesting to consider the good that quantum hype might do. It is, after all, hardly a good thing that most of us (including myself) take our security wholly for granted. If notion of quantum "spookiness" gets people to pay attention to how their stuff is protected, good thing. Just understand that all that stuff isn't being quantum teleported to your laptop.

Reach this writer at michaelb@motherboard.tv.