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Old 16th June 2017, 10:29 PM   #1
alfster Thread Starter
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Default China Shatters “Spooky Action at a Distance” Record, Preps for Quantum Internet

https://www.google.com.au/url?sa=t&r...zez6ftL3fiNDng


Even Einstein struggled to understand this, so I don't feel bad. The best thing about a quantum internet would be it is unhackable.

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Old 17th June 2017, 12:07 AM   #2
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Unhackable?

Brave word.
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Old 18th June 2017, 8:23 PM   #3
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Unhackable?

Brave word.
Einstein agrees with you. It's one of the few things he's been proven wrong about.
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Old 20th June 2017, 12:34 PM   #4
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Errr what?
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Old 20th June 2017, 1:29 PM   #5
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Unhackable?

Brave word.
Probably poor journalism to be using that word, but in a sense this is technology that has communication that cannot be eavesdropped on without the people communicating knowing about it, which is a product of the laws of physics.

I started writing what I know about quantum entanglement, but I think Wikipedia explains it succinctly enough.

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Quantum entanglement is a physical phenomenon that occurs when pairs or groups of particles are generated or interact in ways such that the quantum state of each particle cannot be described independently of the others, even when the particles are separated by a large distance—instead, a quantum state must be described for the system as a whole.

Measurements of physical properties such as position, momentum, spin, and polarization, performed on entangled particles are found to be appropriately correlated. For example, if a pair of particles are generated in such a way that their total spin is known to be zero, and one particle is found to have clockwise spin on a certain axis, the spin of the other particle, measured on the same axis, will be found to be counterclockwise, as to be expected due to their entanglement. However, this behavior gives rise to paradoxical effects: any measurement of a property of a particle can be seen as acting on that particle (e.g., by collapsing a number of superposed states) and will change the original quantum property by some unknown amount; and in the case of entangled particles, such a measurement will be on the entangled system as a whole. It thus appears that one particle of an entangled pair "knows" what measurement has been performed on the other, and with what outcome, even though there is no known means for such information to be communicated between the particles, which at the time of measurement may be separated by arbitrarily large distances.
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Old 21st June 2017, 6:37 AM   #6
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Errr what?
Einstein and others couldn't accept the spooky action at a distance of quantum entanglement. Instead they proposed that there were hidden variables that would define the entire state of the system.

Hidden variable theory.

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Albert Einstein, the most famous proponent of hidden variables, objected to the fundamentally probabilistic nature of quantum mechanics,[1] and famously declared "I am convinced God does not play dice".[2] Einstein, Podolsky, and Rosen argued that "elements of reality" (hidden variables) must be added to quantum mechanics to explain entanglement without action at a distance.[3][4] Later, Bell's theorem suggested that local hidden variables of certain types are impossible, or that they evolve non-locally. A famous non-local theory is De Broglie–Bohm theory.

The more relevant aspect of entanglement is it gives rise to the "no clone rule". So systems such as PRISM just will not work. Not so say that entangled photons cannot be relayed, they can be so long as they're not "read" i.e. collapsed. This is what China has got to work over several repeaters. It's still not very practical as almost all of the entangled photons sent from the satellite are lost in the atmosphere, data throughput is low.
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Old 23rd June 2017, 8:26 AM   #7
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Major flaw in the 'unhackable' theory; it requires the use of a one-time pad and pre-shared key to ensure both integrity/authenticity and confidentiality of the message sent. This actually applies to present day communications.

The journalist was trying to say that this technology will permit us to know when the message has been intercepted along the way, but this would I think still require a one-time pad or prior knowledge of the message sent. As the latter renders the concept useless, only a one time pad provides a basis for this to work.

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In quantum communications, however, these keys can be encoded in various quantum states of entangled photons—such as their polarization—and these states will be unavoidably altered if a message is intercepted by eavesdroppers.
What I expect is that there would be 'padding' added to either end of the message and only these would be necessary to be known to both the sender and receiver, thereby increasing the efficiency of said one-time-pad. Still, I don't think this is necessarily groundbreaking.

Also, I won't believe it until I see it reproduced entirely independently by European, Japanese or American scientists.

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Team leader Jian-Wei Pan—a physicist at the University of Science and Technology of China in Hefei who has pushed and planned for the experiment since 2003—compares the feat with detecting a single photon from a lone match struck by someone standing on the moon. Even so, he says, Micius’s transmission of entangled photon pairs is “a trillion times more efficient than using the best telecommunication fibers. … We have done something that was absolutely impossible without the satellite.”
Bloody hell, imagine the margin for error :| I do hope they don't operate on the presumption that its entirely impossible for their message to have not been reproduced by natural phenomena. If they got one pair for every 6 billion in a second, I suppose a sustained test over a long period of time with a high complex message known at both locations would rule this out?
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Old 23rd June 2017, 3:38 PM   #8
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Unhackable?

Brave word.
A nice side effect of attempting hacking this system will be gaining some knowledge on quantum physics/mechanics :P

Maybe the first hacker of the quantum internet is going to be some quantum physics PhD student doing their thesis :P
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Old 23rd June 2017, 3:48 PM   #9
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For the non quantum savvy, how are the entangled photons "held" both on the ground in China and in the satellite, i assume its more complicated than just putting it in a jar.
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Old 23rd June 2017, 10:47 PM   #10
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For the non quantum savvy, how are the entangled photons "held" both on the ground in China and in the satellite, i assume its more complicated than just putting it in a jar.
You just need the right kind of jar

Cavities Play Catch with Photons.

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Future quantum networks might consist of flying quantum bits made of single photons, captured by nodes that perform computations and send messages. But how easy is it to catch and hold a single photon, for instance, in a small cavity? Researchers in the group of Shengwang Du at the Hong Kong University of Science and Technology have demonstrated that, by shaping its wave function, an individual photon can be loaded into a cavity with near-unity efficiency.
At unity efficiency the cavity would be a perfect "jar".

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Also, I won't believe it until I see it reproduced entirely independently by European, Japanese or American scientists.
They've not done anything others thought impossible or even improbable. They've just succeeded in doing it better.
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Old 18th August 2017, 11:08 PM   #11
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I was watching a video about this kind of particle behavior being part of strong evidence that our perceivable universe is actually a big VR simulation (and likely us also) because the particles act in a easier to process method (wave motion) when not observed, but when you look at them close it gets detailed and changes its behavior.

I know that's old news but its a interesting argument non the less, I mean when you think about it, why should particles care who is watching them and when? but they do....

PS. I know its more complicated then how I explained it. But because physicists still can't explain or agree on what's really happening, it leaves the whole VR universe theory on the table.
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Old 18th August 2017, 11:56 PM   #12
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I saw a show on Foxtel about this Prime2007, the particles behave differently whether anyone is observing them or not, sometimes they are waves & sometimes particles. It seems time can be reversed as well depending on when the scientists decide to look. Spooky action at a distance is literally the weirdest thing I have ever heard of, the scientists haven't got a clue what's going on either.

A big VR simulation you think? Who knows. I lean towards multi universes & multi dimensions myself, but I'm just an average Joe, I didn't even do physics in high school.
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Old 19th August 2017, 8:21 AM   #13
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I was watching a video about this kind of particle behavior being part of strong evidence that our perceivable universe is actually a big VR simulation (and likely us also) because the particles act in a easier to process method (wave motion) when not observed, but when you look at them close it gets detailed and changes its behavior.
What the theory proposes is observation causes the wave function to collapse.
This isn't just something that happens with photons, it can be made to happen with electrons or even atoms and with great care molecules. Truly weird.

I gets weirder. Consider what will happen to my lab rat Alice when I let her fall into a black hole. According to her frame a reference Alice will be just fine, at least just inside the event horizon. According to my frame of reference she's toast.

Logically she cannot be both so how to determine is Alice alive or dead?
It can be done but I'd need a very powerful source of photons, some massive laser. Armed with that I will determine my prediction correct as I toasted poor Alice with my laser. Our universe is a grand conspiracy that we may never fully understand beyond doubt.
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Old 19th August 2017, 2:06 PM   #14
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Either way we seem to be all just play things in this grand scheme (VR).
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