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Network Science

Chinese Physicists Achieve Quantum Teleportation Over 60 Miles 216

Posted by Soulskill from the just-keep-the-shields-up-and-you're-fine dept.
MrSeb writes "Chinese physicists are reporting that they've successfully teleported photonic qubits (quantum bits) over a distance of 97 kilometers (60mi). This means that quantum data has been transmitted from one point to another, without passing through the intervening space. It's important to note that the Chinese researchers haven't actually made a photon disappear and reappear 97 kilometers away; rather, they've used quantum entanglement to recreate the same qubit in a new location, with the same subatomic properties as the original qubit. The previous record for transmitting entangled qubits was 16 kilometers, performed by another Chinese team back in 2010 — and perhaps most excitingly, the researchers seem confident that their system will scale up from 97km to distances capable of reaching orbital satellites, at which point we'll actually be able to build a global quantum network for all of our cryptographic needs."
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Chinese Physicists Achieve Quantum Teleportation Over 60 Miles More

Chinese Physicists Achieve Quantum Teleportation Over 60 Miles

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  • That's nothing (Score:5, Funny)

    by crazyjj ( 2598719 ) * on Friday May 11, 2012 @03:08PM (#39971097)

    I hear the next step is transporting economic superpower status over 7,000 miles.

  • Lord? (Score:5, Funny)

    by i.r.id10t ( 595143 ) on Friday May 11, 2012 @03:11PM (#39971139)

    Lord... Whats a qubit?

    • Re:Lord? (Score:5, Funny)

      by Jose ( 15075 ) on Friday May 11, 2012 @03:17PM (#39971237) Homepage

      Lord... Whats a qubit?

      it is more of who than a what...Qubit is Q*Bert's Chinese cousin.

    • It's a new method for transmitting spam.

    • Re: (Score:3, Funny)

      by osu-neko ( 2604 )

      Lord... Whats a qubit?

      How long can you tread water? :p

    • Re:Lord? (Score:5, Funny)

      by Qubit ( 100461 ) on Friday May 11, 2012 @03:50PM (#39971761) Homepage Journal

      Lord... Whats a qubit?

      Here! I'm here... finally. I would have gotten here sooner if the Chinese hadn't been, you know, teleporting me around all morning.

      *stretches*

      Hmm... well that sucks. I think they made a mistake and put one of my quarks in upside down -- I feel strange all over now.

    • Re:Lord? (Score:5, Informative)

      by FrootLoops ( 1817694 ) on Friday May 11, 2012 @05:58PM (#39973711)

      Here's a summary of the physics, including what a qubit is.

      Quantum states
      Suppose some process produces two electrons. It happens that a particular measurement of a quantum property named spin always comes out as +1/2 or -1/2 for electrons. Now suppose the process that created the electrons must obey a conservation law which forces the sum of the spins of the two electrons to be 0--say the particles that interacted to make the electrons themselves had 0 spin. One electron must then be spin +1/2 and the other must be -1/2. However, until the measurement is performed, you have no idea which is which. More is true: a fundamental part of quantum mechanics is that particle properties can be in multiple states simultaneously right up until a measurement is performed, at which point the property collapses to a single definite value which is randomly chosen based on the relative fractions (actually amplitudes) of the states it used to be in. Thus you can perform a quantum mechanical experiment exactly the same twice without getting the same outcome both times, though you can at least calculate the outcome probabilities. A qubit is simply the state of an electron's spin property before a measurement is made, which in general can be a mix of +1/2 and -1/2. This generalizes to other particles and other two-state properties. (More technically a qubit is an element of a 2-dimensional Hilbert space acting as the state space of some quantum property.)

      Entanglement
      Right after being produced, the two electrons are each in both the +1/2 and -1/2 states. They are "entagled", because if you measure the spin of one electron, from the conservation law you know what a measurement of the other electron's spin must be. Entanglement is actually a very simple consequence of the fact that quantum properties can be in multiple states simultaneously yet conservation laws still need to hold. It's an interesting exercise to try and get faster-than-light communication from this setup, though you'll be unable to. If you're familiar with the relativity of simultaneity, try to both blow up the earth and not by some set of decisions based on the entangled particles' measurements.

      Quantum teleportation
      Using a setup I will not discuss in detail, person A has a qubit encoded in the spin of an electron, and she wants to send the qubit to person B--that is, she wants person B to have an electron with the same spin property in all its mixed-up multiple-states-at-once glory. The setup requires a classical communication channel and some extra entangled particles. Using it, person A can instruct person B to prepare an electron with the same spin state as person A started with. It happens that person A's qubit is destroyed in the process, so the information "teleports", though note that it jumps from one particle to another. The information is all that's teleported, not the particle, and it's not teleported faster-than-light because of the classical communication needed.

  • Ender would be thrilled. (Score:3)

    by rwven ( 663186 ) on Friday May 11, 2012 @03:14PM (#39971195)

    So....how long until we have an Ansible?

    • Just before Jane comes into existence due to the Hive Queen attempt to communicate with the humans.

    • You did notice from the summary how this involves sending photons by laser?

      • If so then the summary of "without crossing the intervening distance" is a lie. The information was encoded and de-encoded for transit,but it still "travelled". No teleportation here, move along, move alone.
        • You're massively oversimplifying. They ARE transmitting information at faster-than-light speed, but only quantum information. Also, in order to verify it, you have to transmit a couple bits of classical information as well, which must cross the intervening distance. No part of quantum teleportation will violate locality or causality, and you should know that by now. It still teleports, its your fault for misunderstanding what that implies.

    • Re:Ender would be thrilled. (Score:5, Informative)

      by Baloroth ( 2370816 ) on Friday May 11, 2012 @03:24PM (#39971363)

      This, and all other quantum "teleportation" and related entanglement phenomenon, do not allow for faster-than-light communication. The important thing to note is that the qubit is "teleported", not the photon itself: the photons are transmitted conventionally via some means (in this case, it looks like they did it through open air). Since the photons are entangled with a photon you retain, measuring one collapses the wave-function of the other and allows both parties to know what the state is simultaneously. The security ramifications are that any eavesdropper will collapse the wave-function before the receiver gets the photon, so he will not receive the photon in the same state as the receiver sent it.

      You cannot, according to what we know of physics, use quantum entanglement to send information faster than light.

      • Re: (Score:3)

        by rwven ( 663186 )

        Grrrr. Foiled again!

      • It's actually worse than that. You could send the photons ahead of time (i.e., you could stock photons and use them to perform teleportation whenever you need it), but teleportation is still not "instantaneous".

        The problem is that, to perform the teleportation, you must first measure the source, and then send the result of the measurement to the destination (that's just 2 bits of classical information). Given this information, the person in the destination chooses one of four measurements to perform in the

      • You cannot, according to what we know of physics, use quantum entanglement to send information faster than light.

        But would it be faster sending information from one side of the Earth to the other than satellites or undersea fiber? If so financial institutions will be all over this.

    • I want Ansibles really badly too, but Quantum Teleportation by definition cannot transmit classical information. Ever. Its a pipedream (and one which would violate causality and locality out the wazoo).

      The only thing you can quantum teleport is quantum information, which is next to useless for anything except a special kind of cryptography
      (which is actually useful. But thats all).

  • Take THAT, Mr Mpaa Riaa! (Score:3)

    by h00manist ( 800926 ) on Friday May 11, 2012 @03:16PM (#39971225) Journal

    Now we won't transfer our warez over any wires or IP numbers at all, and will just teleport the data all over the place.

  • So it's replication (Score:3)

    by HalAtWork ( 926717 ) on Friday May 11, 2012 @03:17PM (#39971235)
    So it's replication, not teleportation?

    • Re: (Score:3, Informative)

      by tstrunk ( 2562139 )

      So it's replication, not teleportation?

      It's not replication, the quantum state of one photon is transfered from one photon to another.
      Here's an easy explanation. http://www.youtube.com/watch?v=_qmSdC7aQpY [youtube.com]

      Replication will never be possible as a quantum state cannot be copied: http://en.wikipedia.org/wiki/No-cloning_theorem [wikipedia.org]

    • Is making an exact copy, I mean EXACT, same quantum properties, same everything, mere replication? I think it goes beyond photocopying. Here's a question; so if its a good (the best) copy of something, does that we might be able to replicate objects ad infinitum? Could some mad asshole make a million Brittany Spears? I quake with fear...
    • No, its quantum teleportation. Quit trying to simplify this, it isn't simple. If you try to simplify it so much, try to find a common metaphor in classical physics, it isn't going to work. You're going to miss a detail and make an assumption. The only thing that this is, is quantum teleportation. It isn't teleportation. It isn't replication.

      Quantum Teleportation is very different from Teleportation.
  • In other news, another group of Chinese Scientists have announced that they have developed a method for filtering teleported qubits which contain information or ideas which are detrimental to the keeping of order of the society.

  • This is not just China's Achievement (Score:5, Funny)

    by l0ungeb0y ( 442022 ) on Friday May 11, 2012 @03:19PM (#39971279) Homepage Journal

    This is part of an international research effort, including schools like Carnegie-Mellon in the US. However, due to the lower costs of photonic qubits in China, it only makes sense to have the majority of experiments carried out over there.

  • Queue starry-eyed 500 posts about Ender's game by people whose idea of being a nerd is playing WoW while they wait for "the singularity", FTL communications, and REAL perpetual motion machines.

    • Its sad, how even among /. you find so many people clearly believing lots of blatant misconceptions about quantum physics. :/
      I mean, shit is definitely complicated, took me awhile to wrap my head around. But don't make assumptions or draw conclusions until you understand something, is that so hard?

  • at which point we'll actually be able to build a global quantum network for all of our cryptographic needs."

    If you think things are bad in Europe with the cameras everywhere and in the USA with the Patriot act and whatnot, you'll find out how good you have it when China is in charge of your cryptographic needs.

  • and half a world away, another butterfly does too.

    not nearly as exciting. boo, science!

  • >> ...their system will scale up...to distances capable of reaching orbital satellites, at which point CHINA actually be able to build a global quantum network for all of CHINA'S cryptographic needs.

    There - fixed that for ya'. Human rights - so 20th century.

  • There is a long, long history in cryptography of systems that were provably secure in principle proving not to be so in practice.

    I'll believe any quantum crypto system is secure after attackers have been pounding on it for a decade or so.

    • This is not just another encryption scheme. What it is, is an encrypted stream, that cannot be intercepted without the knowledge of both sender and receiver. It is theoretically impossible for this to broken.

      • Re: (Score:2)

        by jpapon ( 1877296 )

        It is theoretically impossible for this to broken.

        According to current theory, yes. I agree that it is impossible, as far as we understand things. If faster then light communication was found to be possible, then it seems that this would no longer be secure.

  • Why build a plane when you can TELEPORT the bomb?

  • and perhaps most excitingly, the researchers seem confident that their system will scale up from 97km to distances capable of reaching orbital satellites

    Actually, what would be most exciting would be if they could scale up from qubits to about 86.6 kilograms of organized mass...

  • Once you have the know-how and the hardware to do this, how is 97 km different from 16 km different from across the room?

    Part of this is getting photons from point A to point B. But with fibre optics, couldn't they do 1000 or even 10,000 km with the same effort as 97?

    • The photons must remain in quantum entanglement while one photon is transmitted to the destination. A photon traveling through a glass fiber loses its quantum entanglement fairly rapidly.

  • I'm not sure I get why this method is thought to be any more secure than a conventional line-of-sight laser link.

    It seems as though a line of sight laser that had conventionally encoded data in it would be pretty secure. Well, you'd have to get close to the laser light to observe it, and maybe use some super-fancy optics to couple to it and make a copy of the data. Highly unlikely but possible. But if the (assumed full-duplex) beams were obstructed, the link would be assumed compromised and sending could

    • Conventional lasers use a beam consisting of millions of photons, and some percentage of them have to reach the destination. In the quantum version, individual photons are transmitted, and all must reach the destination, or both transmitter and receiver will know that the secure link has been broken. Additionally, it's theoretically impossible to eavesdrop without either breaking the quantum entanglement, or blocking the photon (or both). Either way, both parties will detect it.

      • Re:Security though overlooking the obvious - (Score:5, Insightful)

        by Darth Snowshoe ( 1434515 ) on Friday May 11, 2012 @04:19PM (#39972291)

        Ah, but the abstract of the paper itself says "Over a 35-53 dB high-loss quantum channel, an average fidelity of 80.4(9) % is achieved for six distinct initial states." That sounds like a lossy channel to me. Plus, I simply don't believe it's possible to send a laser beam over X kilometers, including an atmosphere, and have them ALL reach their destination - it's a limitation of the medium.

        Also, the Physics ArXiv blog post for this paper includes this;
        "Inevitably photons get lost and entanglement is destroyed in such a process. Imperfections in the optics and air turbulence account for some of these losses but the biggest problem is beam widening (they did the experiment at an altitude of about 4000 metres). Since the beam spreads out as it travels, many of the photons simply miss the target altogether. "

        and

        "That's interesting because it's the same channel attenuation that you'd have to cope with when beaming photons to a satellite with, say, 20 centimetre optics orbiting at about 500 kilometres. "The successful quantum teleportation over such channel losses in combination with our high-frequency and high-accuracy [aiming] technique show the feasibility of satellite-based ultra-long-distance quantum teleportation," say Juan and co."

        So it looks to me as though even the paper's author is admitting some "channel losses". The question I still have is, how is it possible to distinguish channel losses from adversarial interception of photons?

        • Well, I went ahead and downloaded the PDF (surprisingly not paywalled).

          It describes it as (paraphrasing slightly):

          Alice has a photon of unknown quantum state and wishes to transfer it to Bob, who is at a distant location. Charlie first distributes an entangled photon pair to Alice and Bob, respectively. Alice now has two photons, and performs a joint Bell-state measurement (BSM) on them. The state of Bob's entangled photon is instantaneously altered by Alice's measurement. Alice then transmits the BSM resul

          • Geez I'm sincerely sorry, I don't mean to pepper you with questions, I should just go ahead and hire on optical physicist to explain this to me, but here goes -

            Is there a way for Alice to discern that a specific entangled photon, sent from Alice (or Charlie) was received by Bob? Alice gets an entangled photon, assumes that Bob has the entangled twin for it, and does her joint Bell-state measurement. Now, Bob's entangle photon is instantaneously altered, right? But Alice doesn't really know whether tha

            • It's not really known whether or not Bob's photon actually changes, or whether it's simply been in the same state as Alice's photon all along. If it changes that would imply that the information moved faster than the speed of light, which poses problems under current models. If it's been that way all along, the only thing that changes is that Alice now knows what state it's in.

              In either case, Alice can tell Bob which quantum operation to perform on the entangled photon to determine the state of Alice's orig

          • So it sounds like the information is not teleported until Bob and Alice have successfully received a pair of entangled photons. Losses simply interfere with Bob's ability to receive entangled photons (Charlie and Alice are in the same physical location).

            ^^^ This.

        • This has been done before. TFA notes that there was a previous record of doing the EXACT SAME THING but over a shorter distance of 16 km.
          The only story here is managing to do it over a long distance.

          Doesn't that inherently imply that there ARE problems? There's difficulty in doing it over larger and larger distances, related to the beams. It just seems obvious, like, DUH they're having problems doing it over longer and longer distances. That is the WHOLE POINT. That's what they're getting better at.

          A

          • Not the exact same thing - quoting from the paper,

            Most recently, following a modified scheme, quantum teleportation over 16 km free-space links was demonstrated with a single pair of entangled photons. However, in this experiment, the unknown quantum state must be prepared on one of the resource entangled qubits and therefore cannot be presented independently. In our experiment, we demonstrate quantum teleportation of an independent unknown state...

            • That's true, but I don't think it changes enough to make a difference for this point. They're sending entangled photons and then sending quantum information about how to read them after, rather than preparing them ahead of time. But both ways they're having to transfer entangled photons over a distance, and I think they're doing it the same way in both.

  • Who is this 'we' you refer to? (Score:3)

    by PPH ( 736903 ) on Friday May 11, 2012 @04:17PM (#39972243)

    at which point we'll actually be able to build a global quantum network for all of our cryptographic needs.

    Are you a member of the Chinese Army?

  • Don't add significant figures (Score:3, Insightful)

    by nedlohs ( 1335013 ) on Friday May 11, 2012 @04:25PM (#39972387)

    It shows a complete lack of understanding of science.

    And of course the actual distance will have been 100km which someone who does understand significant figures converted to 60 miles for Americans. Followed by a moron deciding to convert it to 97 km because they are scientifically illiterate.

    • Re: (Score:3)

      by DerCed ( 155038 )

      No, not at all. It was 97 km. The article is titled "Teleporting independent qubits through a 97 km free-space channel".

  • I still don't really understand entanglement. Any time I hear it explained it sounds like it's really nothing like instantaneous anything. It seems like it's no different than putting two numbers in a hat, pulling one out at random, and then sending the hat to someone and say . . . when I look at mine and send you that info, we both know what yours is!

    • Except that 'when I look at mine', I don't have to 'send you that info', it happens instantaneously. Sending the hat is the only thing that takes time. That's a pretty big difference.

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