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Scientists achieve reliable quantum teleportation for first time (1 Viewer)
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matuski
Footballguy
St. Louis Bob
Footballguy
Dang, I was really close to figuring this out myself.
bostonfred
Footballguy
What color is a mirror? Let's assume you didn't know the answer. Now look at the mirror and tell me what color it is. Well, it's the color of whatever is reflected in it. OK, so move everything away, and let's look again. Well, now I just see the sky. OK, let's try this again, but this time we'll turn off the lights. Nope, still doesn't work, because now I can't see it. If there's light, I see a reflection. If there's no light, I can't see it. That's the observer problem, and it basically means that there are some things that you can't look at the way you look at other things. It's hard to picture, but light is actually a bunch of little particles moving really fast and bouncing off stuff, and when you look at things, you're actually sensing those particles as they reflect back at you, and you use the wavelength to figure out color. Of course, light particles, or photons, aren't like other particles. But that's not the point - they're still particles. And if you want to observe something, the easiest way is to use light.
Unfortunately, just like the mirror problem above, turning the light on screws everything up. Because we're talking about the tiniest imaginable particles, just the act of throwing a bunch of photons at something could screw things up. Which isn't really a problem - there's light bouncing off stuff all the time. But we aren't usually trying to find anything out about those particles. If we want to know what they're up to when nobody's throwing photons at them, we need some way to measure them without seeing them. And there's the rub.
But there's a second problem, and that's the one that cooks your noodle. The second issue is the uncertainty principle, which is why, even if we could figure out how to see particles without messing with them, we still wouldn't be able to do much with the information, because particles don't stop moving. If you don't believe me, take a piece of light and put it on the table. They're constantly moving, and they're almost impossible to pin down.
What Heisenberg said was that while we know there are a lot of particles moving fast, it's hard to narrow down where they are at any given moment in time. We can narrow it down pretty good - like if I point to an ocean and say that there's a drop of water in there somewhere, you'd say, ok, where. But if I showed you a drop of water on your windshield, you could look at it and say, ok, there's my rain drop.
So now let's say you want to find one drop of water in an ocean. Maybe it's way out in the middle of the ocean, or maybe it's right up on the shore - but somehow, I manage to find your drop of water. At the moment I find it, that drop of water might be bobbing up and down peacefully on relatively calm waters, or it might be a little warmer than the other water around it and rising to the surface, or it might be a little cooler and sinking, or it might be lapping up onto the shoreline, or it might be caught in the undertow moving away from the shore. I don't know which way it's going. I can get a general idea, but your specific drop of water? That's going to be tough.
What I could do is I could put some dye in it. But now we're not really looking at a drop of water anymore, we're looking at a drop of dyed water, and that's not very useful when I'm trying to learn how water drops work. Or I could try to narrow things down by looking at something smaller than an ocean, maybe put a box around it so I'm only looking at a little bit of water at a time. But if I make the box too small, my little water droplet is going to be bouncing off the walls, and that screws up all the measurements. I know just where the water drop is, but I have no idea which way it was going when I found it, because it splashed off the wall. And the bigger I make the box, the less precisely I know where my drop is, but the better idea I have of which way it's going.
And that's the issue. You can't really know where a particle is AND where's it's going. You can have a vague idea of each - I know my water drop was up near the surface the last time I saw it, and maybe bobbing up and down with the waves. Or you can try to get a specific idea of one or the other. But you can't get both its position and its momentum. And as far as we can tell, that's not something that's going to change as we get better technology, either.
But even then, it's pretty amazing what we do know, and what we can figure out. I mean, think about splitting an atom. I can split a log with an axe, or a peanut butter sandwich with a knife, but how the #### do you split an atom? And yet they had figured out how to do that 75 years ago (the first uranium atom was split in 1939). They obviously didn't use a knife. They had to smash #### together. It's not splitting the atom in the classic sense. It's a trick they used to make it split.
We use tricks with particles, too. Like the double slit experiment. If you shine a beam of light down on a table that has two slits in it, you'd expect it to work the same way as if you poured water on the table - you'd have two streams of water falling to the floor, one through each slit. But that's not what actually happens, because light particles aren't actually falling. They're moving in waves. And so when they reach the slit, they might be going this way, or that way, or really any which way. So you'd just see that the floor got lit up. But if you make those slits really, really narrow, you start to see something really cool. Instead of dispersing everywhere, it starts to disperse to very specific places, as each photon is either going a little left, or a little right, at the time it passes through the slit. So what you actually see looks like this and this and this. (each picture gets a little more granular as to what's really going on, but what's really going on is counterintuitive enough that a single picture really doesn't do it justice i like the last picture, if you can imagine each one of those little particles moving in a wave pattern instead of a straight line.).
And that makes no sense to us intuitively, because we've observed lots of things going through holes, and it doesn't work that way. Sand in an hourglass? Drops straight down. Air out of a balloon? Sprays straight out. But light is just particles moving in waves, and particles follow their own set of rules. Or maybe a better way of saying it is, particles are the only things that exist, and they follow rules. But we usually don't look at individual particles, we look at bunches of particles clumped together. And while each particle follows those same rules, it's the clumping that makes them act the way we've become accustomed to seeing them act.
So what's happening here in this thread? Well, basically, they figured out another trick. We know that two particles can be paired in such a way that even if you separate them by a really long distance, changing one will cause the other to change instantly. And that's exciting because it means that in theory, information could be passed faster than the speed of light. The problem is, we can't actually know enough about them to make this useful. Because the observer effect means that we can't know what they look like without changing them, and changing them doesn't help us at all if we don't know what they looked like before we changed them.
This is the root of the "no communication" problem - even if we could figure out how to use this trick to share information faster than light, we wouldn't be able to tell when it changed without looking at it, which screws the whole thing up. And that may be an insurmountable problem for communication. But there may be other applications - like the data security one I described on page one of this thread - which would be possible if we could figure out how to observe these things in a scalable way. And this experiment is a relatively big step in the right direction.
PS http://sciencelovelsd.com/uploads/2013/03/double-slit-experiment.png
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joffer
Footballguy
Doctor Detroit
Please remove your headgear
Does this mean the fax machine will someday be irrelevant?
timschochet
Footballguy
Bostonfred, great and fascinating post! 
jamny
Footballguy
You don't disappoint bostonfred. I was hoping you were responding to my question. I only hope to have half the grasp on it that you do.
You've brought me a little closer to understanding as I see how our observation can alter our interpretation of the action. So is the thinking that if we don't observe it, it never happens? Hmmm, if we don't make it happen, it won't happen?
You've brought me a little closer to understanding as I see how our observation can alter our interpretation of the action. So is the thinking that if we don't observe it, it never happens? Hmmm, if we don't make it happen, it won't happen?
bostonfred
Footballguy
This is a really interesting and intuitive question. It's actually at the center of one of the most famous analogies in quantum physics - schroedinger's cat. What schroedinger wanted to show was that an unobserved event was still meaningful and quantifiable. He imagined creating a soundproof, opaque box and putting a cat in it with unlimited food, air and water, but also a trough of poison which had a 50/50 chance of being released. And he said, if you open that box, you might find a dead cat. Or you might find a living cat. But until you open the box, the cat is neither alive nor dead. If anything, its a little of both. So you shouldn't be burying the cat yet, but I wouldn't buy the economy size bag of meow mix, either. And for some reason, that idea blew people's minds.Turns out that a lot of us see that in our day to day lives. If you go all in in a poker game with three of a kind and the other guy has a straight draw and a flush draw, one of you is going to win, and one of you is going to lose, but your odds are pretty close to a coin flip until the cards are flipped. At the moment you see his hand, you're in a kind of limbo where the unobserved turn and river cards already exist in a future where you've won or lost the hand, but the fact that you don't know it yet means that money is neither yours nor his at this time.
See that traffic light up there? Its red right now. But by the time you get there, its about 50/50 to be green. You can either hit the brakes now, and be annoyed if it turns green as you arrive, or coast to it, and have to brake hard if it still hasn't turned green by the time you get there. Based on the best information you have right now it is both red and green for your purposes, even though it will clearly only be one or the other at the time you arrive.
So how do we handle these situations in the real world? We make an educated guess. We bet in poker when we think we have a good chance to win the hand. We don't jam on the brakes when we see a red light up ahead, we kind of coast to it and hope we hit it right. These are normal responses to uncertainty.
Quantum uncertainty is similar. We dont know which way an unobserved particle is spinning right now, but we can estimate the probability and use that in calculations. This idea of using probabilities and expected value calculations instead of actual values led to the famous quote about God playing dice with the universe. It seems wrong to think that a specific particle is either 0 or 1 and assign it an expected value of. 5, when we clearly know that its value is either 0 or 1, and cannot actually be. 5. It seems wrong to say that the light is both green and red - either you should stop, or you should go. But the best decisions are usually made by acknowledging both possibilities, and taking into account how likely each is.
So the answer to your question is no, if you don't observe something, it still happens. But meaningful decisions about how to work with something can be made without actually observing it. We just wont know if they're right until we actually sneak a peek.
Jayrod
Footballguy
heckmanm
Footballguy
Sarnoff
Footballguy
IIRC, in a situation where a quantum particle can behave in multiple ways, it's best though of as a cloud of probability instead of a discrete, individual particle. Until the probability is collapsed into a single result via observation, the Universe generally behaves as if all possibilities do occur simultaneously.Jayrod said:
Brunell4MVP
Footballguy
Quantum physics... This stuff is complex. I will retreat to the who is hottest threads.
CBusAlex
Footballguy
bostonfred
Footballguy
The cat in the box is either alive or dead. It happened before you opened the box. But until the box is open, you don't really know, so in that sense, the cat is neither alive, nor dead. That's what makes it an interesting example. If we had a thousand boxes, it would be pretty reasonable to say that we probably have about five hundred living kitties and five hundred corpses. And if we only have one box, it's reasonable to say that we have half a cat, even though the one thing we know to an absolute certainty is that we don't actually have "half a cat". It's either all the way dead or not dead at all.If you bet $10 on a coin flip, and I flip the coin and catch it in my hand without anyone seeing it, at that moment you still have $10. But the second I open my hand, you either have $20 or $0. One thing's for sure - you won't have $10. So one way of thinking about it is that the action has already occurred, even though it hasn't been observed, and you either have nothing or twenty bucks. The other way of thinking about it is that, as of this moment, the coin is neither heads nor tails, and you have ten bucks.Jayrod said:
We intuitively understand it when they show us looking for a missing airplane and they put a big circle on the TV and say that this is where the plane probably is, so this is our search area. But how do they come up with the circle? Well, we know it had about this much fuel, and last time we saw it, it was going kind of that way, and it was going about so fast, so... I guess it could be anywhere from over here to over there to.. well anywhere in this circle.
The location, spin and momentum of a particle is the same kind of thing. If we want to lock it down to look at any one of those variables, the other ones become impossible to nail down. But based on the probabilities, it ought to be over here in this circle somewhere.
We use probabilities and expected values all the time in our daily lives, often without really realizing it. And at its heart, that's what quantum mechanics is all about. Unlike the missing airplane or the cat in the box or the coin in your hand, in quantum mechanics, you don't get to open up your hand and see whether it was heads or tails. It's not like we are just having a hard time finding particles. It's often more meaningful to refer to their location by their "expected value" than by something more precise. And that's why actually observing it - saying, hey, it's not somewhere in the circle, it's right ####### here - kind of screws up the whole process.
Ignoramus
Footballguy
You mean you can't already?
bostonfred
Footballguy
http://news.stanford.edu/news/2015/november/cryptography-quantum-tangle-112415.html
Researchers from Stanford have advanced a long-standing problem in quantum physics how to send "entangled" particles over long distances.
Their work is described in the online edition of Nature Communications.
Scientists and engineers are interested in the practical application of this technology to make quantum networks that can send highly secure information over long distances a capability that also makes the technology appealing to governments, banks and militaries.
Quantum entanglement is the observed phenomenon of two or more particles that are connected, even over thousands of miles. If it sounds strange, take comfort knowing that Albert Einstein described this behavior as "spooky action."
Consider, for instance, entangled electrons. Electrons spin in one of two characteristic directions, and if they are entangled, those two electrons' spins are linked. It's as if you spun a quarter in New York clockwise, an entangled second coin in Los Angeles would start to spin clockwise. And likewise, if you spun that quarter counter-clockwise, the second coin would shift its spin as well.
Electrons are trapped inside atoms, so entangled electrons can't talk directly at long distance. But photons tiny particles of light can move. Scientists can establish a necessary condition of entanglement, called quantum correlation, to correlate photons to electrons, so that the photons can act as the messengers of an electron's spin.
In his previous work, Stanford physicist Leo Yu has entangled photons with electrons through fiber optic cables over a distance of several feet. Now, he and a team of scientists, including Professor Emeritus Yoshihisa Yamamoto, have correlated photons with electron spin over a record distance of 1.2 miles.
"Electron spin is the basic unit of a quantum computer," Yu said. "This work can pave the way for future quantum networks that can send highly secure data around the world."
To do this, Yu and his team had to make sure that the correlation could be preserved over long distances a key challenge given that photons have a tendency to change orientation while traveling in optical fibers.
Photons can have a vertical or horizontal orientation (known as polarization), which can be referenced as a 0 or a 1, as in digital computer programming. But if they change en route, the connection to the correlated electron is lost.
This information can be preserved in another way, Yu said. He created a time-stamp to correlate arrival time of the photon with the electron spin, which provided a sort of reference key for each photon to confirm its correlation to the source electron.
To eventually entangle two electrons that had never met over great distances, two photons, each correlated with a unique source electron, had to be sent through fiber optic cables to meet in the middle at a "beam splitter" and interact. Photons do not normally interact, just two flashlights beams passing through one another, so the researchers had to mediate this interaction called the "two-photon interference."
To ensure the two-photon interference, they had another issue to overcome. Photons from two different sources have different characteristics, like color and wavelength. If they have different wavelengths, they cannot interfere, Yu said. Before traveling along the fiber optic cable, the photons passed through a "quantum down-converter," which matched their wavelengths. The down-converter also shifted both photons to a wavelength that can travel farther within the fiber optic cables designed for telecommunications.
Quantum supercomputers promise to be exponentially faster and more powerful than traditional computers, Yu said, and can communicate with immunity to hacking or spying. With this work, the team has brought the quantum networks one step closer to reality.
The paper is published online in Nature Communications. In addition to Yu and Yamamoto, it was co-authored by Martin Fejer, Tomoyuki Horikiri, Carsten Langrock, Chandra Natarajan, Jason Pelc, Michael G. Tanner, Eisuke Abe, Sebastian Maier, Christian Schneider, Sven Höfling, Martin Kamp, and Robert H. Hadfield.
The work was supported by the Japan Society for the Promotion of Science, the National Science Foundation, the National Institute of Information and Communications Technology, the National Institute of Standards and Technology, Special Coordination Funds for Promoting Science and Technology, and the State of Bavaria. Funding also came from the Air Force Office of Scientific Research, SU2P Entrepreneurial Fellowship and Royal Society University Research Fellowship.
MEDIA CONTACT
Leo Yu, Applied Physics: leoyu@stanford.edu
Researchers from Stanford have advanced a long-standing problem in quantum physics how to send "entangled" particles over long distances.
Their work is described in the online edition of Nature Communications.
Scientists and engineers are interested in the practical application of this technology to make quantum networks that can send highly secure information over long distances a capability that also makes the technology appealing to governments, banks and militaries.
Quantum entanglement is the observed phenomenon of two or more particles that are connected, even over thousands of miles. If it sounds strange, take comfort knowing that Albert Einstein described this behavior as "spooky action."
Consider, for instance, entangled electrons. Electrons spin in one of two characteristic directions, and if they are entangled, those two electrons' spins are linked. It's as if you spun a quarter in New York clockwise, an entangled second coin in Los Angeles would start to spin clockwise. And likewise, if you spun that quarter counter-clockwise, the second coin would shift its spin as well.
Electrons are trapped inside atoms, so entangled electrons can't talk directly at long distance. But photons tiny particles of light can move. Scientists can establish a necessary condition of entanglement, called quantum correlation, to correlate photons to electrons, so that the photons can act as the messengers of an electron's spin.
In his previous work, Stanford physicist Leo Yu has entangled photons with electrons through fiber optic cables over a distance of several feet. Now, he and a team of scientists, including Professor Emeritus Yoshihisa Yamamoto, have correlated photons with electron spin over a record distance of 1.2 miles.
"Electron spin is the basic unit of a quantum computer," Yu said. "This work can pave the way for future quantum networks that can send highly secure data around the world."
To do this, Yu and his team had to make sure that the correlation could be preserved over long distances a key challenge given that photons have a tendency to change orientation while traveling in optical fibers.
Photons can have a vertical or horizontal orientation (known as polarization), which can be referenced as a 0 or a 1, as in digital computer programming. But if they change en route, the connection to the correlated electron is lost.
This information can be preserved in another way, Yu said. He created a time-stamp to correlate arrival time of the photon with the electron spin, which provided a sort of reference key for each photon to confirm its correlation to the source electron.
To eventually entangle two electrons that had never met over great distances, two photons, each correlated with a unique source electron, had to be sent through fiber optic cables to meet in the middle at a "beam splitter" and interact. Photons do not normally interact, just two flashlights beams passing through one another, so the researchers had to mediate this interaction called the "two-photon interference."
To ensure the two-photon interference, they had another issue to overcome. Photons from two different sources have different characteristics, like color and wavelength. If they have different wavelengths, they cannot interfere, Yu said. Before traveling along the fiber optic cable, the photons passed through a "quantum down-converter," which matched their wavelengths. The down-converter also shifted both photons to a wavelength that can travel farther within the fiber optic cables designed for telecommunications.
Quantum supercomputers promise to be exponentially faster and more powerful than traditional computers, Yu said, and can communicate with immunity to hacking or spying. With this work, the team has brought the quantum networks one step closer to reality.
The paper is published online in Nature Communications. In addition to Yu and Yamamoto, it was co-authored by Martin Fejer, Tomoyuki Horikiri, Carsten Langrock, Chandra Natarajan, Jason Pelc, Michael G. Tanner, Eisuke Abe, Sebastian Maier, Christian Schneider, Sven Höfling, Martin Kamp, and Robert H. Hadfield.
The work was supported by the Japan Society for the Promotion of Science, the National Science Foundation, the National Institute of Information and Communications Technology, the National Institute of Standards and Technology, Special Coordination Funds for Promoting Science and Technology, and the State of Bavaria. Funding also came from the Air Force Office of Scientific Research, SU2P Entrepreneurial Fellowship and Royal Society University Research Fellowship.
MEDIA CONTACT
Leo Yu, Applied Physics: leoyu@stanford.edu
bostonfred
Footballguy
Moore's law says that computing power doubles every two years. Quantum computing would blow that away, and they're making significant gains. Lifi (WiFi using light instead of radio waves) is potentially 1000 times faster than wifi, and is already in significant testing. Quantum teleportation could involve communication over interstellar distances, and importantly, without wires. And they're figuring things out which were thought to be unfigureoutable.
The Internet changed the world in ways we couldn't imagine 25 years ago. Copper wire and land line telephones were still the standard at that time. This stuff is orders of magnitude more powerful than either of those leaps. And we could see those changes start to happen in our lifetime.
Baloney Sandwich
Footballguy
The only I really want to understand about all this stuff is how can I make boatloads of money off of it?
Jayrod
Footballguy
Dinsy Ejotuz
Footballguy
tdoss... once two particles are entangled changes happen to both of them simultaneously -- regardless of how far apart they are. It's like time (and distance) ceased to exist. No electrical impulse running through a wire -- once something happens to one of them it happens in both places at the exact same moment.
If you want to have your mind blown completely apart go read what some super serious scientists are writing about the implications of entanglement (eg the Holographic Universe). I can only follow some of it, but it's more than a little scary.
If you want to have your mind blown completely apart go read what some super serious scientists are writing about the implications of entanglement (eg the Holographic Universe). I can only follow some of it, but it's more than a little scary.
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matttyl
Footballguy
Otis
Footballguy
bostonfred
Footballguy
The idea of entanglement is that two particles are connected without touching. Theoretically it doesn't matter how far apart they are. Changing one results in an instant change to the other. Nobody knows exactly how or why and it's very difficult to observe. If you ever read enders game by Orson Scott Card, he talked about a device called an ansible that was basically a video conference over the Internet in space, which used exactly this principle to instantly communicate from earth to other systems. Not bad considering how old the book is.
bostonfred
Footballguy
There are Internet enabled LEDs which broadcast an Internet signal using imperceptible sub millisecond light flickers that are faster than the fastest WiFi. I know some surfing is best done with the lights off or maybe just a candle or something, but it's an option.
tdoss
Footballguy
Fascinating...I guess what was throwing me is the article that bfred just posted mentions using photons across a good distance...I'm assuming to check the correlation between the two entangled particles?So...it's instantaneous...but we can only prove up to light speed since we're using photons to check that correlation, right?
How are they entangling these particles and then separating them by great distance?
Is there a limit to the distance of this entanglement?
What's "binding" these elements across this great distance?
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captain_amazing
Footballguy
That's literally never happened to me. Have I never been entangled quantumly?smoke monster said:
Brony
Footballguy
nice post, you stupid dunce!
Galileo
Footballguy
The speed of information transfer in quantum entanglement is about 3,000,000,000,000 m/s. Sort of...possibly...maybe...
http://www.physics-astronomy.com/2014/04/chinese-physicists-measure-speed-of_16.html
http://www.physics-astronomy.com/2014/04/chinese-physicists-measure-speed-of_16.html
grateful zed
Footballguy
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