
Quantum 'spooky action at a distance' becoming practical? - dnetesn
https://phys.org/news/2018-01-quantum-spooky-action-distance.html
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TipVFL
Quantum entanglement is such a neat phenomenon, but secure communication feels
like such a boring application. How much extra security would a quantumly
protected communication channel provide over just using some really heavy
encryption sent in a normal manner?

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alex_anglin
That observation of the communication would break the link, versus capture and
(attempt to) decrypt?

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Klathmon
That to me seems like the coolest possibility.

Encryption that breaks if someone other than the authorized parties observes
it. Something which isn't possible with "traditional" encryption.

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nsxwolf
Sounds like a denial of service attack though. Just keep trying to read
messages and render the channel unusable.

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QAPereo
If you have secrets to keep, and your adversaries have that kind of access,
better a DDOS than a leak.

Edit: _This kind of observation would already require physical access to the
communications medium (e.g. a fiber optic cable). So if you could DoS a
quantum encrypted channel by measuring it, you could equally well DoS a
classical channel by just cutting the fiber._

The comment just above mine, which does a better job than me of explaining the
degree of access required.

Besides which, it’s not as though you can _only_ use this. You try your
quantum channel first, and if it’s down you know you’re under attack, and act
accordingly with your Classical backups.

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thaumasiotes
Well, the whole point of encryption is that you can send your message through
despite the fact that your adversary can see it.

Replacing that with a system where your adversary can't see your message, and
neither can your correspondent, is a downgrade, not an upgrade.

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mathw
That depends entirely on your application.

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thaumasiotes
Could you give some examples of applications of encryption where the purpose
is not to send a message that adversaries may see but cannot understand?

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eru
Encrypting data at rest, for example. (Depends on how wide your definition of
'send' is.)

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QAPereo
[http://advances.sciencemag.org/content/4/1/e1701230.full](http://advances.sciencemag.org/content/4/1/e1701230.full)

Original paper, in case you don’t want to slog through Phys.org’s brand of
press release nonsense.

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Roritharr
"This was possible to achieve thanks to state of art photon source and
detection technology"

What's a photon source thats not a lamp/laser?

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deepnotderp
You usually need single photon sources or SPDC.

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comstock
Don’t you need SPDC to get entangled photons anyway?

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albutr
No, it's just one particular method of creating entangled pairs, e.g. there
are integrated semiconductor devices that can be used to generate them using
other physical effects (but AFAIK SPDC is what most people use in practical
situations)

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comstock
Interesting, do you have any search terms I could use to google for the
semiconductor devices (I’ll try myself, but if you have a jumping off point
that would be helpful).

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albutr
Sure, one example that I'm familiar with is frequency entangled photons
produced by parametric scattering of exciton-polaritons (it's scattering of
quasiparticles in a quantum well which are strongly coupled to a photon
field). Although, I actually can't recall if I've seen a convincing
experimental demonstration of this.

I have seen a bunch of experimental results which demonstrated entanglement
using integrated silicon waveguides, where there are two waveguides that
overlap in an effective "beam splitter" section then separate again (this is
analogous to how you can get entanglement from an Hong-Ou-Mandel setup, which
is two (EDIT: identical photons) incident on a 50/50 beam splitter which
produces so-called "path entangled" photons).

Here's a recent short review paper which goes over some additional
semiconductor devices which can produce entangled photon pairs[1].

[1] [https://arxiv.org/abs/1702.08823](https://arxiv.org/abs/1702.08823)

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xbmcuser
Sadly even if we achieve quantum communication it will be only be for military
and governments as we have already seen how government and law enfrocement all
over the world has been against secure communication between people.

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QAPereo
I’m as dystopian and paranoid as the next guy, but come on... we’re using the
results of ARPANET night now. Our devices have GPS. We can use whatever
encryption we like (for now). The governments of most of the world
monopolizing a means of communication for long, is unlikely.

