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back to article Australian unis to test quantum-comms-over-fibre

The University of New South Wales, one of the world's leaders in quantum computing research, will get the chance to put its work to the test in Australia's capital city, Canberra. Within a few months, two nodes on Canberra's ICON network – one at the Australian National University, the other at the Australian Defence Force …

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Silver badge

Hmmm....

Should a third party intercept or observe the key, the loss of entanglement should be measurable to the recipient since the entanglement is destroyed.

What if the third party uses a system similar to that described in http://www.theregister.co.uk/2013/06/03/quantum_boffins_get_spooky_with_time/ ?

If that could work, they would be able to measure the transmitted photon but still end up with a photon entangled with the original photon which they could resend...

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Joke

Re: Hmmm....

A third party, somewhere between Campbell and Acton, intercepting communications ... now, who would do a thing like that? Maybe that's another reason they chose those locations ...

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Joke

Re: Hmmm....

I can just see it now....

*Phone rings* Hullo?

Hey George, it's Frank. Did you see my reply to your email?

WTF? I'm still writing that email and haven't sent it yet.

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Please explain

Whenever anyone criticises research into 'quantum communication' or 'quantum computing', or the fact that it is never clear how they work, he gets panned. Would somebody please explain, simply, how these things can be brought about - how the theory can be made to work in practical applications? And what the benefits are likely to be? That would be very cool - thanks in advance!

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Anonymous Coward

Re: Please explain

"Would somebody please explain, simply, how these things can be brought about - how the theory can be made to work in practical applications? And what the benefits are likely to be? That would be very cool - thanks in advance!"

It's quite simple, using analogies:

Telegraph is like a very very long cat. You pull his tail in New York and he meows in Los Angeles.

Radio operates exactly the same way, only there is no cat.

Quantum communication operates the same way again, only you have two cats, one at each end. Oh, and they're really the same cat... but at the same time they're not really the same cat. And only when you make them be the same cat (but not really the same cat). And only until they're not the same cat anymore.

See, simples!

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Re: Please explain

See, simples!

Ah, but that's no mere cat you have there!

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Idle Question

Will a quantum computer be able to decrypt a message encrypted using a quantum-entangled key by simultaneously trying all possible entangled key values?

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Silver badge

Re: Idle Question

Yes, but all you'll get from that is every possible result -- you'll still have to sift through them and test each one contextually to determine if its the correct result.

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Alien

Of course it is the correct result!

And an incorrect result!

and all the somewhat correct results!

All at once, unless they are entangled in time too... which will give all those results before you ask the question.

My head hurts now, time for my nap.

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Anonymous Coward

I thought I understood the article

Then I read the comments. Now my head hurts.

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Pishtosh

When two states become entangled, a complete account of the properties of one of the systems is not possible if it does not include the other system; and this will be true no matter how far apart the two systems may be spatially. Therefore, you cannot KNOW entanglement has happened. You must ASSUME it has on the basis of a similar diffraction pattern. Nobody, no matter how they spin it has not communicated through entangled particles. Entanglement does transmit "classical information", and therefore cannot be used for communication at faster than light speed. It's Hokum.

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re: Pishtosh

Wow... chill. Nobody's saying that entanglement allows instantaneous information transfer. The way this works is (roughly) that we send some photons using a recorded polarisation, the receiver sets up some polarising filters at random and then both parties communicate the results using standard (non-FTL) communication channels. The quantum magic happens because an eavesdropper can't know both the initial polarisation and the polarisation setting at the detector and any attempt to "copy" the photon in flight has at least a 50/50 chance of getting the polarisation wrong (assuming only two polarisation settings), thus alerting Alice and Bob to Eve's presence.

The whole system (from emitter to detector) is the quantum entanglement "experiment", so it's easy to see how an eavesdropper will prematurely collapse the probability waveform, ruining the values that Bob sees. But again, even though in normal operation, without an eavesdropper, the collapse is instantaneous with the measurement at the detector end, Alice and Bob still need to communicate their results before they actually know what that measurement means, so there's no FTL information transfer... so it's actually not Hokum.

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Anonymous Coward

Someone should do an "Anonymous PhD" feature

just so people can see how many highly educated supergeniuses we have on here.

Add a special icon for:- BSc, MSc, MEng, PhD, postgrad, etc.

AC

and where the hell is my quantum broadband already?

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