Chinese Physicists Smash Distance Record For Teleportation
technologyreview.com
technologyreview.com
Imagine two indistinguishable envelopes. Put a red piece of paper in one of them and a green piece of paper in the other. Shuffle them so you don't know which is which. Have a friend take one of the envelopes a hundred kilometers away. Then open the envelope you still have with you. It contains the green piece of paper. WHOA INSTANT TELEPORTATION OF INFORMATION! You know that the other envelope has the red paper instantly, even though it is a hundred kilometers away! Information transfer faster than the speed of light. Amazing.
Now, instead of using envelopes, imagine Alice generates a pair of entangled photons. Alice send one half to Bob and measures the other half. Since the photons are entangled, Alice knows what Bob must be measuring, just like with the envelopes. So what makes quantum teleportation special? What can we do with quantum teleportation that we cannot do with envelope teleportation?
One interesting thing about the quantum world is that we cannot measure something without disturbing it. You can use that property to make an ultra-secure cryptographic system.
Alice generates an entangled photon pair so that the photons are either 'pointing left' or 'pointing right' or 'pointing up' or 'pointing down'. Now, there is no way to measure directly what direction the photon is pointing in. You can choose among two tests. Test A gives you the correct answer if the photon is pointing left or right, but gives you a random result if it's pointing up or down. Test B gives you the correct result if it's pointing up or down but a random result if it's pointing right or left.
Doing Test A or Test B completely disturbs the photon, giving it a random state.
If Alice chooses a direction to measure randomly, and Bob chooses a direction to measure randomly, Bob's measurements will agree with Alice 75% of the time. Half the time, they'll choose the same method and their measures will agree, and half the time they will choose a different method and both get a random result, but through pure chance, they will still agree half the time.
If Eve tries to do a 'Man in the middle' attack, intercepting Alice's photons and copying the result to send to Bob, Eve will send with only 75% accuracy and Bob's measurements will be only 62.5% accurate. Thus, Eve can be detected. Watch this video for more details: http://www.youtube.com/watch?v=UVzRbU6y7Ks
This result in the link is interesting because the researchers have been able to transport an 'entangled' photon over more than 100 kilometers, maintaining its state. It is quite hard to do since entangled photons are fragile.
However, the photons are not being teleported, just transmitted, and sticking to the speed limit like good space citizens. It is not that Alice can make a change to her half of the entangled pair and have that be reflected in Bob's, it's just that Alice can MEASURE her half and know what Bob must be measuring.
http://en.wikipedia.org/wiki/Quantum_teleportation
An entangled qubit is created and half of it is stored at location A, and half of it is stored at location B. That's the insecure part, but once A and B have two halves of the qubit, the rest of the communication is guaranteed secure.
It's amazing that you can make a change to the half at A, and its reflected in the half at B, because they are quantum entangled. Now B has no idea how to interpret the change since it seems random, but A sends a kind of "public key to unlock the data" over the air to B, and B can use that to measure his half and extract the data.
The data is "teleported", but the public key used to read the data is open. The public key itself tells you nothing about the data. It's brilliant.
Mind = blown.
I just don't think having the most secure quantum cryptographic communication system is the type of technology they would gladly want to share with the rest of world. Sooner or later, the secret service (do they have one?) or military will be involved. Will we see another Cold War-ish information technology race?
You make it sound as if this selfishness and militaristic lean is specifically Chinese in nature and that other freedom-lovin', rainbow-kissin' nations engage in free and open exchange of knowledge with no military aspirations whatsoever. "Oh if only those poor misguided Chinese shared like the rest of us do we wouldn't have another cold-war." I mean I understand why you might be prejudiced to think that way because I presumably live in the same NATO bubble as you do, but this kind of "our values vs. their values" thinking is the exact Hollywood-like narrative that starts wars in the first place (and by that I'm not accusing only westerners of this, I'm pretty sure it happens in China too).
But while technology might be used for purposes of conflict, I think that the digital age also has the potential to break the barriers of distrust and xenophobia between people of different nations. It's sort of happening on a small scale already. You are able to have a conversation with a person in China (when their internet is not being blocked) and realize that they are not a DVD-copying, cat-eating, environment-hating communist that your society might suggest they are. Governments often use the lack of knowledge about different nations to justify going to war or blocking trade. Maybe with the new age of global digital awareness we will not have such an easy time cultivating distrust and hate. Or maybe it's gotten to the point where we all distrust and hate each other on an individual level.. in which case we're all fucked
What world do you live in?
How do you stop Carol from just grabbing the entangled photon herself and reading the information? How can Alice know that Bob received the entangled photon? Even Carol as a MITM seems possible if she just sent Bob new entangled photons
The trick has always been in encrypting the aggregate information. But, I am sure that quantum cryptography will be a completely different ball game compared to what we have now.
You aren't teleporting the photons, you're teleporting via the photons. What's in the way matters only for getting the photons to the destination.
The operator at Station 1 performs a measurement on a particle there that changes the spin of that particle, as well as a measurement on a desired quantum bit that we want to transmit to Station 2. This process produces 2 classical bits of information. This process destroys the correlation between the particle pair, and affects the particle at Station 2 but in a randomized way that is useless without the operator at Station 2 possessing the two classical bits (thus it is not faster-than-light communication).
Once the laser takes the two classical bits to Station 2, at the speed of light, the operator at Station 2 can use them to decide what measurement to perform on the paired particle. Once the correct measurement is performed, the quantum bit that we measured at Station 1 appears.
The security benefit is that by completing one risky journey from Station 1 to Station 2, we can allow many future quick, secure journeys.
The propagation happens at the speed of light because the classical bits are required to understand what has been teleported. Performing the measurements is much slower than the speed of light. The correlation can only be stored for very short periods of time, currently.
It also bothers me that the article specifically says the "information" is teleported, as it seems like the author is going out of his/her way to imply a violation of the No Communication Theorem (http://en.wikipedia.org/wiki/No-communication_theorem), which is not in any way violated by the experiment.
And that is how a scanning-tunneling microscope works.