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Chinese scientists test quantum entanglement over unprecedented distance

scientificamerican.com

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Re: Chinese scientists test quantum entanglement over unprecedented distance

#41

Post by berdon »

novalis78 wrote: post #40
lucozade wrote: post #37

Earlier quoted context omitted.

With quantum entanglement, what happens to one particle prior to measurement affects the other even if the effect occurred after they were parted. That's where it gets really spooky. To belabour the colours and boxes analogy: We have 2 balls, if one is orange the other is always purple and vice versa. Now these balls have an extra property. If you shake them vigorously they may or may not change colour randomly. So,…

Sounds like they never were two separate entities to begin with or never parted location. Which is spooky too, in a different way.

Too build on this thought - is it possible that these quantum properties aren't affected by locality? Which is obviously true given the explanation above... I guess I'm asking if there are other intuitions that can be made if locality is explicitly considered unrelated.

Re: Chinese scientists test quantum entanglement over unprecedented distance

#42

Post by darkerside »

lucozade wrote: post #37
gabrielgoh wrote: post #19

Earlier quoted context omitted.

i fail to see whats mysterious about knowing something without direct proof. You could put a literal orange cube in a box, ship it across the galaxy, and you'd "know" anyone opening the box would be an orange cube. You don't need to be present at the unboxing to know that with certainty. How is this different? Am I missing something?

With quantum entanglement, what happens to one particle prior to measurement affects the other even if the effect occurred after they were parted. That's where it gets really spooky. To belabour the colours and boxes analogy: We have 2 balls, if one is orange the other is always purple and vice versa. Now these balls have an extra property. If you shake them vigorously they may or may not change colour randomly. So,…

What is the equivalent to "shaking" in QM? I'm trying to figure out why it matters whether you shake the box or not (i.e. could the shaking simply not have an effect if you're not looking?)

Re: Chinese scientists test quantum entanglement over unprecedented distance

#43

Post by JPLeRouzic »

fsiefken wrote: post #27

Could you use this for untraceable communication with hidden non-traceable submerged subs? That would be a military advantage.

Thanks to your comment I am now daydreaming of a neutrino radio, with a design inspired from a Fusor!

Re: Chinese scientists test quantum entanglement over unprecedented distance

#45

Post by lucozade »

darkerside wrote: post #42
lucozade wrote: post #37

Earlier quoted context omitted.

With quantum entanglement, what happens to one particle prior to measurement affects the other even if the effect occurred after they were parted. That's where it gets really spooky. To belabour the colours and boxes analogy: We have 2 balls, if one is orange the other is always purple and vice versa. Now these balls have an extra property. If you shake them vigorously they may or may not change colour randomly. So,…

What is the equivalent to "shaking" in QM? I'm trying to figure out why it matters whether you shake the box or not (i.e. could the shaking simply not have an effect if you're not looking?)

The shaking represents any sort of action that doesn't perform a measurement. It was the first thing I thought of that could affect the ball without opening the box.

It could be that the shaking didn't have an effect. But equally, it could have had an effect. The spooky bit is that the other ball 'knows' whether it did or not in a non-local way.

Re: Chinese scientists test quantum entanglement over unprecedented distance

#46

Post by greeneggs »

sliken wrote: post #6

A staple of sci-fi has been a pair of boxes with quantum entangled particles inside allowing FTL communications once the boxes travel (sub-FTL) to their destination. By my understanding that's impossible, although I always wondered if you could coordinate FTL, by detecting when a particle was no longer entangled. Can someone with the background comment?

> A staple of sci-fi has been a pair of boxes with quantum entangled particles inside allowing FTL communications once the boxes travel (sub-FTL) to their destination.

Of course this is complete nonsense. It's useful for plotting stories, but seems to have imprinted on a large fraction of readers a total falsehood. Do you know where the idea started? I think the first time I saw it was in Orson Scott Card's novel "Ender's Game" (1985).

Re: Chinese scientists test quantum entanglement over unprecedented distance

#47

Post by swashbuck1r »

heimdall wrote: post #17
sliken wrote: post #6

A staple of sci-fi has been a pair of boxes with quantum entangled particles inside allowing FTL communications once the boxes travel (sub-FTL) to their destination. By my understanding that's impossible, although I always wondered if you could coordinate FTL, by detecting when a particle was no longer entangled. Can someone with the background comment?

Caveat: I only have a B.Science degree in Engineering Physics (Colorado, USA) and hobbyist-type research in PhD-level physics. I've always found it easier to explain quantum entanglement thusly: Imagine you have 2 cubes that alternate glowing between purple and orange. And they stay in one color for a random amount of time (100s of milliseconds). Holding both in your hands, you would just have randomly color-shifting…

[I'm not a physicist] I like your analogy for color entanglement. However, it doesn't show the "weirdness" of superposition (the balls don't have a concrete value until one of the boxes are opened, at which point, this triggers the determination of the open box's color value), nor the "spookiness" of action-at-a-distance (opening one box instantly influences the state of the ball in the other box -- which now must be the opposite color when its box is opened).

Intuitively, someone might think: well, the ball colors were "decided" while the two balls were next to each other (ballA will be orange, ballB will be purple), and the information about the color is attached to the balls, so the balls know what color to be when they are separated and later opened (they have "hidden variables" indicating the assigned color)....however, the reality (provable statistically by Bell's Theorem) is that the balls do not carry this color information, and instead the act of opening the box, randomly sets the color of BallA and instantly affects the color that BallB will have.

So if both people synchronize the time to open the box (that has some time relativity problems), so that BoxA is opened a fraction of a second before BoxB, then BoxA's color will influence BoxB's color (seen a fraction of a second later), but that will have happened faster than the speed of light would allow if BoxA was sharing its color information with BoxB.

Re: Chinese scientists test quantum entanglement over unprecedented distance

#48

Post by pacman128 »

Illniyar wrote: post #2

I thought quantum entanglement is the idea that two quantum particles separated by distance will behave the same at the same time regardless od distance. Why is sending photons over distances a verification of quantum entanglement? Can someone elaborate on what this is?

Another factor to consider is that relativity showed that whether two events at different locations are simultaneous depends on the observer's reference frame. See (https://en.wikipedia.org/wiki/Relativity_of_simultaneity). So you can't even say which measurement of the state is the one that collapses the waveform. Observers in different reference frames would disagree.

Re: Chinese scientists test quantum entanglement over unprecedented distance

#49

Post by Strilanc »

EGreg wrote: post #8

Wikipedia says: " If Bohmian Mechanics as an non-local hidden variables interpretation of quantum mechanics is accurate it should allow quantum computers to implement a search of an N-item database at most in O ( N 3 ) {\displaystyle O({\sqrt[{3}]{N}})} steps. This is slightly faster than the O ( N ) O({\sqrt {N}}) steps taken by Grover's algorithm using standard interpretations of quantum mechanics. Neither search m…

It's just a wrong statement. Follow the reference to the paper and see:

> [...] we show that if we could examine the entire history of a hidden variable, then we could efficiently solve [...]

Bohmian mechanics doesn't give you access to the entire history of a hidden variable.

Re: Chinese scientists test quantum entanglement over unprecedented distance

#50

Post by MrZongle2 »

greeneggs wrote: post #46
sliken wrote: post #6

A staple of sci-fi has been a pair of boxes with quantum entangled particles inside allowing FTL communications once the boxes travel (sub-FTL) to their destination. By my understanding that's impossible, although I always wondered if you could coordinate FTL, by detecting when a particle was no longer entangled. Can someone with the background comment?

> A staple of sci-fi has been a pair of boxes with quantum entangled particles inside allowing FTL communications once the boxes travel (sub-FTL) to their destination. Of course this is complete nonsense. It's useful for plotting stories, but seems to have imprinted on a large fraction of readers a total falsehood. Do you know where the idea started? I think the first time I saw it was in Orson Scott Card's novel "En…

Looks like it may have started in 1966 with a story by Ursula K. Le Guin. She called the device an ansible, which is what it was also called in OSC's books.

https://en.wikipedia.org/wiki/Ansible

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