Quantum Teleportation over 10-miles

Seen something interesting in the news or on the intertubes? Discuss it here.

Moderators: Zamfir, Hawknc, Moderators General, Prelates

Dark Avorian
Posts: 546
Joined: Mon May 03, 2010 10:48 pm UTC

Quantum Teleportation over 10-miles

Postby Dark Avorian » Thu May 20, 2010 11:04 pm UTC

arstechnica

Spoiler:
Quantum teleportation achieved over ten miles of free space
by Casey Johnston | Last updated May 19, 2010 6:40 AM
Quantum teleportation has achieved a new milestone or, should we say, a new ten-milestone: scientists have recently had success teleporting information between photons over a free space distance of nearly ten miles, an unprecedented length. The researchers who have accomplished this feat note that this brings us closer to communicating information without needing a traditional signal, and that the ten miles they have reached could span the distance between the surface of the earth and space.
As we've explained before, "quantum teleportation" is quite different from how many people imagine teleportation to work. Rather than picking one thing up and placing it somewhere else, quantum teleportation involves entangling two things, like photons or ions, so their states are dependent on one another and each can be affected by the measurement of the other's state.
When one of the items is sent a distance away, entanglement ensures that changing the state of one causes the other to change as well, allowing the teleportation of quantum information, if not matter. However, the distance particles can be from each other has been limited so far to a number of meters.
Teleportation over distances of a few hundred meters has previously only been accomplished with the photons traveling in fiber channels to help preserve their state. In this particular experiment, researchers maximally entangled two photons using both spatial and polarization modes and sent the one with higher energy through a ten-mile-long free space channel. They found that the distant photon was still able to respond to changes in state of the photon they held onto even at this unprecedented distance.
However, the long-distance teleportation of a photon is only a small step towards developing applications for the procedure. While photons are good at transmitting information, they are not as good as ions at allowing manipulation, an advancement we'd need for encryption. Researchers were also able to maintain the fidelity of the long-distance teleportation at 89 percent— decent enough for information, but still dangerous for the whole-body human teleportation that we're all looking forward to.


Wow, 89% of information over 10 miles, I personally find that rather impressive.
The 62-foot tall statue of Jesus constructed out of styrofoam, wood and fiberglass resin caught on fire after the right hand of the statue was struck by lightning.


meatyochre wrote:And yea, verily the forums crowd spake: "Teehee!"

Glass Fractal
Posts: 497
Joined: Thu May 13, 2010 2:53 am UTC

Re: Quantum Teleportation over 10-miles

Postby Glass Fractal » Thu May 20, 2010 11:33 pm UTC

Wait a second, I thought there was some reason you couldn't use entanglement to transmit information.

Dark Avorian
Posts: 546
Joined: Mon May 03, 2010 10:48 pm UTC

Re: Quantum Teleportation over 10-miles

Postby Dark Avorian » Thu May 20, 2010 11:45 pm UTC

Yeah, that confused me too...although when this talks about choosing ions over photons it suggests that we can manipulate it. I'm getting a bit confused...
The 62-foot tall statue of Jesus constructed out of styrofoam, wood and fiberglass resin caught on fire after the right hand of the statue was struck by lightning.


meatyochre wrote:And yea, verily the forums crowd spake: "Teehee!"

Duban
Posts: 352
Joined: Fri May 01, 2009 1:22 pm UTC

Re: Quantum Teleportation over 10-miles

Postby Duban » Thu May 20, 2010 11:45 pm UTC

Glass Fractal wrote:Wait a second, I thought there was some reason you couldn't use entanglement to transmit information.

I think it is possible to read the signal but doing so changes the state of the particles. I think the basic idea is the same as QE. While it's possible to read it's impossible to intercept the single without changing it. It is also physically impossible to listen in on a quantum communication of any sort. Why? because anyone who attempts to listen in will damage the signal and give away their existance.

Of course i must admit i'm not a particle physicist either...
Last edited by Duban on Fri May 21, 2010 1:17 am UTC, edited 2 times in total.
It is not the gods I fear. No, It is those who claim to speak for them that concern me.

Glass Fractal
Posts: 497
Joined: Thu May 13, 2010 2:53 am UTC

Re: Quantum Teleportation over 10-miles

Postby Glass Fractal » Fri May 21, 2010 12:00 am UTC

Duban wrote:
Glass Fractal wrote:Wait a second, I thought there was some reason you couldn't use entanglement to transmit information.

No not really, it is possible to read the signal but doing so changes the state of the particles. So while it's possible to read it's impossible to intercept the single without changing it. One of the biggest advantages is it's physically impossible to listen in on a quantum communication. Why? because anyone listening in will damage the signal and give away their existance.

Of course i must admit i'm not a particle physicist either...


That sounds like quantum encryption rather than quantum teleportation.

Duban
Posts: 352
Joined: Fri May 01, 2009 1:22 pm UTC

Re: Quantum Teleportation over 10-miles

Postby Duban » Fri May 21, 2010 12:52 am UTC

Glass Fractal wrote:
Duban wrote:
Glass Fractal wrote:Wait a second, I thought there was some reason you couldn't use entanglement to transmit information.

No not really, it is possible to read the signal but doing so changes the state of the particles. So while it's possible to read it's impossible to intercept the single without changing it. One of the biggest advantages is it's physically impossible to listen in on a quantum communication. Why? because anyone listening in will damage the signal and give away their existance.

Of course i must admit i'm not a particle physicist either...


That sounds like quantum encryption rather than quantum teleportation.

Ok, I could be entirely wrong, but I thought the basic idea of sending and measuring the information stayed the same. The main difference was how the information was transfered "this time it was sent through quantum entanglement". I guess it would somewhat impossible to intercept in the first place, but you still need to send the photon. I don't know, maybe i'm entirely wrong.
It is not the gods I fear. No, It is those who claim to speak for them that concern me.

User avatar
big boss
Posts: 589
Joined: Tue Mar 23, 2010 7:59 am UTC

Re: Quantum Teleportation over 10-miles

Postby big boss » Fri May 21, 2010 1:03 am UTC

Glass Fractal wrote:Wait a second, I thought there was some reason you couldn't use entanglement to transmit information.


You are correct. Imagine a simple situation. A particle at rest with 0 spin decays decays into one electron and one positron traveling in the opposite directions at the same speed (conservation of momentum, energy). To conserve spin one must have spin up and one must have spin down, but according to quantum mechanics both particles have indeterminate spin until they are measured (one cannot say that one particle has spin up and the other down, the actual state is a "smear" of the spin up and down state). Now image these particles are allowed to travel so that they are across the galaxy to two different points, A and B. A person at point A makes a measurement and finds the particle there with spin up, this instantaneously collapses the entangled wave functions and the other particle at B instantaneously knows to take a "stand" and have a down spin (without being constrained by the speed of light). Now relativistically this should be impossible, however you cannot transmit information this way (because the observers have no way to pick what spin the particle they measure will have, its "random", therefore they cannot transmit any kind of information) and therefore it does not go against relativity.
"Starbuck, what do you hear?"
"Nothing but the Rain."

User avatar
frezik
Posts: 1336
Joined: Wed Jan 10, 2007 7:52 pm UTC
Location: Schrödinger's Box

Re: Quantum Teleportation over 10-miles

Postby frezik » Fri May 21, 2010 3:39 am UTC

Glass Fractal wrote:Wait a second, I thought there was some reason you couldn't use entanglement to transmit information.


To add to what big boss said, you can never transmit information faster than light. You can use quantum effects to transmit information, as long as you're obeying the Universal Speed Limit while you do it.
I do not agree with the beer you drink, but will defend to the death your right to drink it

User avatar
Gelsamel
Lame and emo
Posts: 8237
Joined: Thu Oct 05, 2006 10:49 am UTC
Location: Melbourne, Victoria, Australia

Re: Quantum Teleportation over 10-miles

Postby Gelsamel » Fri May 21, 2010 3:50 am UTC

Which, unless you're sending out entangled particles faster than the speed of light, you are.
"Give up here?"
- > No
"Do you accept defeat?"
- > No
"Do you think games are silly little things?"
- > No
"Is it all pointless?"
- > No
"Do you admit there is no meaning to this world?"
- > No

User avatar
big boss
Posts: 589
Joined: Tue Mar 23, 2010 7:59 am UTC

Re: Quantum Teleportation over 10-miles

Postby big boss » Fri May 21, 2010 4:44 am UTC

Gelsamel wrote:Which, unless you're sending out entangled particles faster than the speed of light, you are.


But the whole idea of quantum entanglement relies on an instantaneous collapse of the particle's wavefunction which travels faster than the speed of light no matter what the distance the two particles are separated by.
"Starbuck, what do you hear?"
"Nothing but the Rain."

User avatar
Gelsamel
Lame and emo
Posts: 8237
Joined: Thu Oct 05, 2006 10:49 am UTC
Location: Melbourne, Victoria, Australia

Re: Quantum Teleportation over 10-miles

Postby Gelsamel » Fri May 21, 2010 4:58 am UTC

big boss wrote:
Gelsamel wrote:Which, unless you're sending out entangled particles faster than the speed of light, you are.


But the whole idea of quantum entanglement relies on an instantaneous collapse of the particle's wavefunction which travels faster than the speed of light no matter what the distance the two particles are separated by.


Except you have to seperate the particles to begin with...

If I entangle 2 sets of particles and attempt to send the message "Hello World!" to you I have to actually send the second set of particles to you so I can measure and collapse your particles so you can read it. To send you those particles would take some amount of time under or equal to that of the speed of light.

Also, wave function collapse is not necessarily instantaneous.
"Give up here?"
- > No
"Do you accept defeat?"
- > No
"Do you think games are silly little things?"
- > No
"Is it all pointless?"
- > No
"Do you admit there is no meaning to this world?"
- > No

User avatar
big boss
Posts: 589
Joined: Tue Mar 23, 2010 7:59 am UTC

Re: Quantum Teleportation over 10-miles

Postby big boss » Fri May 21, 2010 6:03 am UTC

Gelsamel wrote:Except you have to seperate the particles to begin with...

If I entangle 2 sets of particles and attempt to send the message "Hello World!" to you I have to actually send the second set of particles to you so I can measure and collapse your particles so you can read it. To send you those particles would take some amount of time under or equal to that of the speed of light.


Not disagreeing with you there, sorry if i made it sound that way

Gelsamel wrote:Also, wave function collapse is not necessarily instantaneous.


Both textbooks that I have in front of me right now claim the collapse is instantaneous, do you have any proof of this, or can provide a certain example when its not instantaneous?
"Starbuck, what do you hear?"
"Nothing but the Rain."

User avatar
LuNatic
Posts: 973
Joined: Thu Nov 20, 2008 4:21 am UTC
Location: The land of Aus

Re: Quantum Teleportation over 10-miles

Postby LuNatic » Fri May 21, 2010 6:54 am UTC

Why do they insist on calling it teleportation when it isn't?

To add to what big boss said, you can never transmit information faster than light. You can use quantum effects to transmit information, as long as you're obeying the Universal Speed Limit while you do it.


I thought the whole point of quantum entanglement communication was that no signal travel is involved, therefore the speed of light is irrelevant?

Duban wrote:
Glass Fractal wrote:Wait a second, I thought there was some reason you couldn't use entanglement to transmit information.

I think it is possible to read the signal but doing so changes the state of the particles.


Schrodinger's lolcat?
Cynical Idealist wrote:
Velict wrote:Good Jehova, there are cheesegraters on the blagotube!

This is, for some reason, one of the funniest things I've read today.

User avatar
Malice
Posts: 3894
Joined: Sat Jul 21, 2007 5:37 am UTC
Location: Los Angeles, CA
Contact:

Re: Quantum Teleportation over 10-miles

Postby Malice » Fri May 21, 2010 7:58 am UTC

LuNatic wrote:Why do they insist on calling it teleportation when it isn't?


Because there's no real word for what they're doing, and the word teleportation makes me feel (a) like I'm in the future and (b) like buying the newspaper whose headline I'm currently reading.
Image

User avatar
Sizik
Posts: 1260
Joined: Wed Aug 27, 2008 3:48 am UTC

Re: Quantum Teleportation over 10-miles

Postby Sizik » Fri May 21, 2010 8:36 am UTC

big boss wrote:
Glass Fractal wrote:Wait a second, I thought there was some reason you couldn't use entanglement to transmit information.


You are correct. Imagine a simple situation. A particle at rest with 0 spin decays decays into one electron and one positron traveling in the opposite directions at the same speed (conservation of momentum, energy). To conserve spin one must have spin up and one must have spin down, but according to quantum mechanics both particles have indeterminate spin until they are measured (one cannot say that one particle has spin up and the other down, the actual state is a "smear" of the spin up and down state). Now image these particles are allowed to travel so that they are across the galaxy to two different points, A and B. A person at point A makes a measurement and finds the particle there with spin up, this instantaneously collapses the entangled wave functions and the other particle at B instantaneously knows to take a "stand" and have a down spin (without being constrained by the speed of light). Now relativistically this should be impossible, however you cannot transmit information this way (because the observers have no way to pick what spin the particle they measure will have, its "random", therefore they cannot transmit any kind of information) and therefore it does not go against relativity.


How would this be different from the two particles having their spins set when they're created? Either way, you won't know the spin of the particle until you measure it, and it would still be a 50% chance of either being up or down.
she/they
gmalivuk wrote:
King Author wrote:If space (rather, distance) is an illusion, it'd be possible for one meta-me to experience both body's sensory inputs.
Yes. And if wishes were horses, wishing wells would fill up very quickly with drowned horses.

User avatar
Gelsamel
Lame and emo
Posts: 8237
Joined: Thu Oct 05, 2006 10:49 am UTC
Location: Melbourne, Victoria, Australia

Re: Quantum Teleportation over 10-miles

Postby Gelsamel » Fri May 21, 2010 9:05 am UTC

big boss wrote:
Gelsamel wrote:Also, wave function collapse is not necessarily instantaneous.


Both textbooks that I have in front of me right now claim the collapse is instantaneous, do you have any proof of this, or can provide a certain example when its not instantaneous?


According to quantum decoherence, as far as I am aware, the wave function collapse is not instantaneous. Also I'm pretty sure it is verified that you can use weak measurements to probe quantum states and then prevent the collapse (see http://arxiv.org/abs/0708.0365 and http://www.science.org.au/nova/newscien ... ns_002.htm).

Your textbooks probably initially discuss at least a few other interpretations of quantum mechanics, then usually they'll say something like they'll only be looking at the Copenhagen interpretation in which I'm pretty sure the wave function collapse is considered instantaneous (not up to scratch on my quantum tbh).
"Give up here?"
- > No
"Do you accept defeat?"
- > No
"Do you think games are silly little things?"
- > No
"Is it all pointless?"
- > No
"Do you admit there is no meaning to this world?"
- > No

User avatar
Aardvarki
Posts: 129
Joined: Tue Jul 17, 2007 3:51 pm UTC

Re: Quantum Teleportation over 10-miles

Postby Aardvarki » Fri May 21, 2010 2:58 pm UTC

Neat. Let me know when Teleportation will let me go to the Bahamas.
-Aa
Weeks wrote:The only Dexter I really know is the one with the lab

User avatar
Zamfir
I built a novelty castle, the irony was lost on some.
Posts: 7604
Joined: Wed Aug 27, 2008 2:43 pm UTC
Location: Nederland

Re: Quantum Teleportation over 10-miles

Postby Zamfir » Fri May 21, 2010 7:08 pm UTC

Sizik wrote:
big boss wrote:
Glass Fractal wrote:Wait a second, I thought there was some reason you couldn't use entanglement to transmit information.


You are correct. Imagine a simple situation. A particle at rest with 0 spin decays decays into one electron and one positron traveling in the opposite directions at the same speed (conservation of momentum, energy). To conserve spin one must have spin up and one must have spin down, but according to quantum mechanics both particles have indeterminate spin until they are measured (one cannot say that one particle has spin up and the other down, the actual state is a "smear" of the spin up and down state). Now image these particles are allowed to travel so that they are across the galaxy to two different points, A and B. A person at point A makes a measurement and finds the particle there with spin up, this instantaneously collapses the entangled wave functions and the other particle at B instantaneously knows to take a "stand" and have a down spin (without being constrained by the speed of light). Now relativistically this should be impossible, however you cannot transmit information this way (because the observers have no way to pick what spin the particle they measure will have, its "random", therefore they cannot transmit any kind of information) and therefore it does not go against relativity.


How would this be different from the two particles having their spins set when they're created? Either way, you won't know the spin of the particle until you measure it, and it would still be a 50% chance of either being up or down.


You don't use quantum entanglement to send the message, you use it to send (and generate) a key. If you send 1000 (entangled) particles to a receiver, you can both measure them and you will both have an identical, random 1000-bit key. You can then use that key to encrypt a 1000-bit message and send it through a normal channel. With some careful scheming, you can make sure that eavesdropping gets noticed.

It has absolutely nothing to do with teleporting, I am afraid.

User avatar
Amnesiasoft
Posts: 2573
Joined: Tue May 15, 2007 4:28 am UTC
Location: Colorado
Contact:

Re: Quantum Teleportation over 10-miles

Postby Amnesiasoft » Sat May 22, 2010 7:25 am UTC

Duban wrote:It is also physically impossible to listen in on a quantum communication of any sort. Why? because anyone who attempts to listen in will damage the signal and give away their existance.

I do believe just recently saw an article refuting this. I just don't remember where. But the basic idea was if they don't induce too many errors in the information stream, it doesn't trigger the threshold that is considered "secure."

EDIT: Ha, found it: http://www.technologyreview.com/blog/arxiv/25189/ Obviously, it's not really practical for stealing keys, but it does show you can't necessarily guarantee someone isn't listening.

User avatar
Gelsamel
Lame and emo
Posts: 8237
Joined: Thu Oct 05, 2006 10:49 am UTC
Location: Melbourne, Victoria, Australia

Re: Quantum Teleportation over 10-miles

Postby Gelsamel » Sat May 22, 2010 10:26 am UTC

Amnesiasoft wrote:
Duban wrote:It is also physically impossible to listen in on a quantum communication of any sort. Why? because anyone who attempts to listen in will damage the signal and give away their existance.

I do believe just recently saw an article refuting this. I just don't remember where. But the basic idea was if they don't induce too many errors in the information stream, it doesn't trigger the threshold that is considered "secure."

EDIT: Ha, found it: http://www.technologyreview.com/blog/arxiv/25189/ Obviously, it's not really practical for stealing keys, but it does show you can't necessarily guarantee someone isn't listening.


Actually if you see my article above, it talks about measuring quantum states with weak measurements and then reversing the measurement so that wave function doesn't collapse so QM Cryptography is in a bad spot at the moment...
"Give up here?"
- > No
"Do you accept defeat?"
- > No
"Do you think games are silly little things?"
- > No
"Is it all pointless?"
- > No
"Do you admit there is no meaning to this world?"
- > No

User avatar
Welsh Mullet
Posts: 54
Joined: Wed Jan 27, 2010 9:58 pm UTC
Location: South Wales

Re: Quantum Teleportation over 10-miles

Postby Welsh Mullet » Sat May 22, 2010 11:59 am UTC

So, if nothing can travel faster than light, this means there would be a delay between sending and receiving, right? (otherwise, does it break physics? or does this quantum physics not have to obey normal physics?)

What if you set your end to up, but while it was sending, the one at the other end was found to also be up?

User avatar
Indon
Posts: 4433
Joined: Thu Oct 18, 2007 5:21 pm UTC
Location: Alabama :(
Contact:

Re: Quantum Teleportation over 10-miles

Postby Indon » Sat May 22, 2010 12:21 pm UTC

The article mentions they were able to detect when they tinkered with one of the photons. That in and of itself can be used to send information, I should think, even if you can't actually determine what the particle's spin's supposed to be.

It seems we're close to being able to loophole that speed-of-light limitation in the theory of relativity, if we haven't yet already.
So, I like talking. So if you want to talk about something with me, feel free to send me a PM.

My blog, now rarely updated.

Image

User avatar
lowbart
Posts: 668
Joined: Sun Dec 09, 2007 10:00 pm UTC
Location: northeastern USA
Contact:

Re: Quantum Teleportation over 10-miles

Postby lowbart » Mon May 24, 2010 12:04 pm UTC

Indon wrote:The article mentions they were able to detect when they tinkered with one of the photons. That in and of itself can be used to send information, I should think, even if you can't actually determine what the particle's spin's supposed to be.

It seems we're close to being able to loophole that speed-of-light limitation in the theory of relativity, if we haven't yet already.


Yeah, if you can notice when it instantaneously changes to match, wouldn't that mean that you could send binary messages through [1= change] [0= no change] ?
...a fish called the Henamo grunter, named because it makes grunting noises from its swim bladder.
v1nsai wrote:Yes, I'm Linux, how can I help you ma'am?

Kain
Posts: 1140
Joined: Wed Aug 27, 2008 4:29 am UTC
Location: At the center of the observable universe.

Re: Quantum Teleportation over 10-miles

Postby Kain » Mon May 24, 2010 5:51 pm UTC

lowbart wrote:
Indon wrote:The article mentions they were able to detect when they tinkered with one of the photons. That in and of itself can be used to send information, I should think, even if you can't actually determine what the particle's spin's supposed to be.

It seems we're close to being able to loophole that speed-of-light limitation in the theory of relativity, if we haven't yet already.


Yeah, if you can notice when it instantaneously changes to match, wouldn't that mean that you could send binary messages through [1= change] [0= no change] ?


Wouldn't that be somewhat impracticle due to completely random perturbations giving false readings? I recall reading something along what you suggested in some science fiction book, and at one point my q mech professor mentioned something about something similar to that being untenable (sorry, I slept through most of q mech, will have to retake it next spring).
Look, you know it's serious when a bunch of people in full armor and gear come charging in to fight a pond of chickens - Steax

User avatar
Zamfir
I built a novelty castle, the irony was lost on some.
Posts: 7604
Joined: Wed Aug 27, 2008 2:43 pm UTC
Location: Nederland

Re: Quantum Teleportation over 10-miles

Postby Zamfir » Mon May 24, 2010 6:27 pm UTC

lowbart wrote:
Indon wrote:The article mentions they were able to detect when they tinkered with one of the photons. That in and of itself can be used to send information, I should think, even if you can't actually determine what the particle's spin's supposed to be.

It seems we're close to being able to loophole that speed-of-light limitation in the theory of relativity, if we haven't yet already.


Yeah, if you can notice when it instantaneously changes to match, wouldn't that mean that you could send binary messages through [1= change] [0= no change] ?

No, you can't measure on your photon that the other side has measured theirs. All you know as that the outcome of your measurement is in a fixed way related to their measurement, independent of who measures first.

For most situations, entanglement works as if you have two boxes, one with a black marble and one with a white marble in it. You send one random box somewhere else, and if you then open your box and find a white marble you know the other side must have the black marble.

The weird thing (which can be experimentally proven) as that in quantum entanglement, the random choice for black or white is only made at the opening of the box, not before. Yet both sides will agree. But the effect is random, so you can't influence the outcome after you send one box away.

User avatar
Goldstein
Posts: 985
Joined: Wed Nov 05, 2008 9:38 pm UTC
Location: Newcastle, UK

Re: Quantum Teleportation over 10-miles

Postby Goldstein » Thu May 27, 2010 8:11 am UTC

Zamfir wrote:The weird thing (which can be experimentally proven) as that in quantum entanglement, the random choice for black or white is only made at the opening of the box, not before.

This is, understandably, the part that I find most counter-intuitive. Could you link me to some sort of explanation? I can't imagine how it might be possible to prove that.
Chuff wrote:I write most of my letters from the bottom

nopacman
Posts: 38
Joined: Fri Nov 27, 2009 11:14 pm UTC

Re: Quantum Teleportation over 10-miles

Postby nopacman » Thu May 27, 2010 3:48 pm UTC

Well, I think the quantum eraser experiment is related to this, and provides quite an example.
http://grad.physics.sunysb.edu/~amarch/

User avatar
gmalivuk
GNU Terry Pratchett
Posts: 26823
Joined: Wed Feb 28, 2007 6:02 pm UTC
Location: Here and There
Contact:

Re: Quantum Teleportation over 10-miles

Postby gmalivuk » Thu May 27, 2010 4:34 pm UTC

lowbart wrote:
Indon wrote:The article mentions they were able to detect when they tinkered with one of the photons. That in and of itself can be used to send information, I should think, even if you can't actually determine what the particle's spin's supposed to be.

It seems we're close to being able to loophole that speed-of-light limitation in the theory of relativity, if we haven't yet already.
Yeah, if you can notice when it instantaneously changes to match, wouldn't that mean that you could send binary messages through [1= change] [0= no change] ?
Yes. If you [magic], then that totally means you could [magic]. Unfortunately, you can't.

The situation Indon is talking about, where you can detect when someone tinkered with one of the photons, is like this:
A------->B------->C
And at C you can detect whether B tampered with the stream of photons being sent from A. The magic would be this:
B<-------A------->C
with C still being able to detect when B had tampered with B's photon. But that isn't something that can happen faster than light, so there's no loophole.
Last edited by gmalivuk on Thu May 27, 2010 4:44 pm UTC, edited 1 time in total.
Unless stated otherwise, I do not care whether a statement, by itself, constitutes a persuasive political argument. I care whether it's true.
---
If this post has math that doesn't work for you, use TeX the World for Firefox or Chrome

(he/him/his)

User avatar
Indon
Posts: 4433
Joined: Thu Oct 18, 2007 5:21 pm UTC
Location: Alabama :(
Contact:

Re: Quantum Teleportation over 10-miles

Postby Indon » Thu May 27, 2010 4:42 pm UTC

Hmm, yeah, it seems I misread that part of the article. They were just saying, "When we measured to see if they were at some point entangled, they probably still were," instead of "We collapsed the waveform and were able to detect when we did so because they were entangled."

nopacman wrote:Well, I think the quantum eraser experiment is related to this, and provides quite an example.
http://grad.physics.sunysb.edu/~amarch/


I knew all of that theoretically, but illustrated in that way it's still hard to wrap my head around.
So, I like talking. So if you want to talk about something with me, feel free to send me a PM.

My blog, now rarely updated.

Image

User avatar
Goldstein
Posts: 985
Joined: Wed Nov 05, 2008 9:38 pm UTC
Location: Newcastle, UK

Re: Quantum Teleportation over 10-miles

Postby Goldstein » Thu May 27, 2010 6:21 pm UTC

Yeah, that's cleared that up for me; at least, I agree with the conclusions - I don't think the goings-on in that experiment will ever be clear to me. Thanks nopacman.
Chuff wrote:I write most of my letters from the bottom

User avatar
tendays
Posts: 957
Joined: Sat Feb 17, 2007 6:21 pm UTC
Location: HCMC

Re: Quantum Teleportation over 10-miles

Postby tendays » Mon May 31, 2010 11:05 am UTC

From my understanding, the point of quantum teleportation is to transmit an *unknown* quantum state from a particle to another that can be arbitrarily far away, which is distinct from quantum cryptography whose point is to construct a shared bit string between two people for use as a one time pad, while detecting eavesdropping.

Quantum teleportation is done in four phases:
1) Physically place two entangled particles at the two locations between which teleportation is to be performed.
2) Have one of those particles interact with the quantum state to be transmitted (at this point the quantum state is lost at the source, and is instantly transported to the destination, but is scrambled and not yet usable)
3) Transmit the results of the measurement done in 2 from the source to the target over a classical channel (this step is limited by the speed of light).
4) At the target, use the information transmitted at 3 to "unscramble" the other entangled particle. The target particle is now in the desired state, (which is still unknown and can't be obtained in any way).

It is interesting because step 1 can be done before the quantum state to be transmitted even exists, so you could send a large number of entangled pairs, for use for later state teleportation. Then you only need a classical communication channel to exchange quantum information.

EDIT: TFA says "without needing a traditional signal". I don't see how that can be right. Both quantum cryptography and quantum teleportation require a traditional signal to be sent between the parties before they do anything useful.
<Will> s/hate/love/
Hammer wrote:We are only mildly modly. :D
Beware of the shrolymerase!

Robstickle
Posts: 326
Joined: Sat Nov 28, 2009 10:07 am UTC

Re: Quantum Teleportation over 10-miles

Postby Robstickle » Mon May 31, 2010 12:45 pm UTC

Guys you're missing what's truly important here.

Spoiler:
Latency free video games!


Return to “News & Articles”

Who is online

Users browsing this forum: iamspen and 15 guests