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Network Science

Physicists Demonstrate Quantum Router 81

Posted by Soulskill
from the but-does-it-run-dd-wrt dept.
Diggester tips news that physicists from Tsinghua University in China have published "the first proof-of-principle demonstration of a genuine quantum router." The group's paper (PDF) is available at the arXiv. MIT's Technology Review describes it thus: "In this new device, the information is encoded in the polarization of photons, either horizontal or vertical. The Chinese group begin by creating a single photon that is in a superposition of both horizontal and vertical polarization states. They then convert this single photon into a pair of lower energy photons that are entangled, a process called parametric down conversion. Both of these photons are also in a superposition of polarization states. The router works by using the polarization of one of these photons as the control signal to determine the route of the other, the data signal. The device is simple, little more than a collection of half mirrors for guiding photons and waveplates for rotating their polarization."
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Physicists Demonstrate Quantum Router

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  • by sycodon (149926) on Friday August 03, 2012 @03:08PM (#40871483)

    ...I'll start getting at least half of the advertised speed from my AT&T DSL connection?

  • by Anonymous Coward

    But what about the quantum backdoors implanted for the Chinese government?

    • But what about the quantum backdoors implanted for the Chinese government?

      Quick, somebody lock down quantumbackdoors.com for use as a porn site.
      When the Chinese government tries to use their secret backdoor they will encounter a black hole!

    • Even not specified in the article, one of the photons of the entangled pair belongs to the Chinese government. That's what we call an entangled backdoor.
  • It should be obvious to anyone with an advanced degree in polygonal quantum mechanics that you can encode information "in the polarization of photons, either horizontal or vertical" and using a Chinese group that began by "creating a single photon that is in a superposition of both horizontal and vertical polarization states. They then convert this single photon into a pair of lower energy photons that are entangled, a process called parametric down conversion. Both of these photons are also in a superposit

    • by P-niiice (1703362)
      well, you take one Chinese group that began by "creating a single photon that is in a superposition of both horizontal and vertical polarization states. They then convert this single photon into a pair of lower energy photons that are entangled, a process called parametric down conversion. Both of these photons are also in a superposition of polarization states. The router works by using the polarization of one of these photons as the control signal to determine the route of the other, the data signal. The
      • by Shavano (2541114)
        All except the control part. What they can apparently do is MEASURE which way the photon WENT using the entangled partner.
    • by mooingyak (720677)

      Can anybody explain this using something simple, like stuffed bunnies?

      You got this stuffed bunny, right? Then you rip him in half, but the halves still remember being part of the whole bunny, so they're half-bunnies, but they're still part of the whole bunny. And then you transmit info between the bunny pieces.

      • by P-niiice (1703362)
        If you can understand how sanrda lee bakes a cake, you can understand this.

        SANDRA LEE [occasion] CAKE
        1. Get one (1) cake
        2. Add icing and cookies and decorations for [occasion] all over the cake.
        3. Done.
        • by mooingyak (720677)

          But to comply with the OP's request, it would need to be a bunny cake.

          • by Ichijo (607641)

            Since every piece of matter in the Universe is in some way affected by every other piece of matter in the Universe, it is in theory possible to extrapolate the whole of creation - every Galaxy, every sun, every planet, their orbits, their composition, and their economic and social history from, say, one small piece of bunny cake. (Paraphrased from HHGTTG)

            • by EdIII (1114411)

              I like that.

              Since "one small piece of bunny cake" is quite arbitrary, it could just as easily be anything else. Also consider the axiom that knowledge is power.

              This leads to the inescapable conclusion, according to your theory, that my penis is all-knowing and all-powerful.

    • Certainly.

      Take two stuffed bunnies. Lay one on its side, and stand the other on its head. These are two "polarizations".

      But with QUANTUM stuffed bunnies, it is possible to create a pair of stuffed bunnies that are actually in both positions at the same time... "superposition"... and "entangled", meaning the the positions of both are linked. (This has also led to the creation of a new illustrated book, the Quanta Sutra... but that's another story.)

      So, you send these superposed stuffed bunnies down
    • by Darinbob (1142669)

      You shine a light through some half mirrors, the beam of lights split and one is polarized one way and the other beam is polarized the other way. It's just like all that stuff you saw in undergrad physics labs except that you use words like quantum entanglement and superposition.

      (ya it's more complex than this but that was my mental image when I read the summary and before I read the article)

  • by liquidpele (663430) on Friday August 03, 2012 @03:16PM (#40871557) Journal
    Yes.... I understand some of these words...
  • This router is very ...... enlightening..... I wonder how light it is... Is it going to be light on the pocket book too when it comes out?
    • by rts008 (812749)

      Is it going to be light on the pocket book too when it comes out?

      No.

      It will create a black hole in your wallet that won't stop until you have lost your ass.

      It's just simple consumerism, but you were mistaken that you are the consumer, instead of the consumed....

      • It will create a black hole in your wallet that won't stop until you have lost your ass.

        That just leaves one question: how did a photograph of this phenomenon slip backwards in time to become the Goatse guy?

  • by Dins (2538550) on Friday August 03, 2012 @03:19PM (#40871595)
    How long until we have a working Ansible [wikipedia.org]?
    • by Jamu (852752)
      Never or yesterday.
    • Actually I was thinking more of something like that, but with store/drain, depending on how far entanglement goes and how long you can maintain it.

      Think about 1 meter entanglement range. You entangle two particles, shift one a meter away. It takes time to move that particle, of course; but once it's entangled, flipping one flips the other instantly.

      Bandwidth like this is infinite. If you have 1Gbit/s real bandwidth and can store 3000Gbit of entangled particles stably. and they're stable for 3000 second

      • by Anonymous Coward

        but once it's entangled, flipping one flips the other instantly.

        No it won't, that's not how entanglement works. It's more like you have two quarters, and if you flip both they will always land with the same face up. Mucking with the flipping (forcing it one way or the other) will break the pattern; the pattern only shows up when you flip them both and let them do their thing.

      • by Lithdren (605362)
        I'm no expert in this, but I dont think you understand whats going on here at all. Flipping one doesn't instantly flip the other. You cant communicate information via entanglement.

        Please, someone correct me if im wrong, but my understanding is its like having a red, and blue ball in seperate bags. You throw one ball (in its bag) across the room, then open the other bag. The open bag is blue, you now know the red one is across the room.

        You've gained information but you haven't actually transfered any
        • Re:So... (Score:4, Interesting)

          by ByteSlicer (735276) on Friday August 03, 2012 @04:43PM (#40872629)

          Please, someone correct me if im wrong, but my understanding is its like having a red, and blue ball in seperate bags. You throw one ball (in its bag) across the room, then open the other bag. The open bag is blue, you now know the red one is across the room.

          It's more like having two balls, both half-red half-blue, in separate bags. The balls contain a magnet that causes them to align: when one is red-up, the other is blue-up.

          Then you shake the bags, open one, and pick out the ball. If it's red-up, you'll know the other ball will be blue-up, and vice versa.

          At first glance this may look the same as your model with the full red or blue ball (a so called hidden variable model), but the statistics differ from real entanglement (which includes superposition of states).

          In the first (classical) model FTL information transfer is impossible because nothing is actually transferred. The ball was blue or red to begin with, and opening the bag doesn't change that.

          In the second (quantum) model FTL information transfer actually does occur (with entanglement, the magnet alignment in the model occurs slower than light obviously). But the observer can't choose what this information will be: picking a ball out of a bag will result in a random color. And the other bag will then contain a ball in the opposite but equally random color. You can't pick the color, so you can't choose the message/information.

          Statistics from experiments have shown that the second model is the correct one, and that entanglement and the FTL state transfer are real.

        • by TexVex (669445)

          I'm no expert in this, but I dont think you understand whats going on here at all. Flipping one doesn't instantly flip the other. You cant communicate information via entanglement.

          This is correct.

          Please, someone correct me if im wrong, but my understanding is its like having a red, and blue ball in seperate bags. You throw one ball (in its bag) across the room, then open the other bag. The open bag is blue, you now know the red one is across the room.

          This is not correct. What you are describing is c

        • I'm no expert in this, but I dont think you understand whats going on here at all. Flipping one doesn't instantly flip the other. You cant communicate information via entanglement.

          Well, I'm no expert in this, but you're wrong. You can't transfer information faster than light; what you can do is transfer an entangled particle at the speed of light, and then tap one particle and read the other to see what happened with it. Across 300 light years, if you manipulate particle A[0}, particle A[1] instantly reflects its new state; however it does take 300 years to get particles A[0] and A[1] 300 light years apart. You can't just wake up and decide to transmit 3 gigabytes of information w

      • I think you're confusing bandwidth and latency. Bandwidth will be limited by how many bits/second your hardware can process, latency is the part where transmission times factor in. Since each of your relays would still have to process the information to pass it on you maximum bandwidth wouldn't increase.

        The way I pictured it was, assuming you could figure out how to keep the photons entangled indefinitely, you could send a stream of photons to Alpha Centauri while keeping their entangled pairs in some sor

        • You can only send 1 gigabit across a 1 gigabit link; but if your hardware is fast enough to process 1 terrabit/s, you could send that. We don't have 1Tb links, though there's 10GbE. Also entanglement isn't instant over distance; it's limited by the speed of light, i.e. two particles 1 light year apart take at a minimum a year to entangle. You can do this by entangling two particles together and then moving them apart, or if you find a magic way to entangle two particles that are far apart you can do that

          • by Immerman (2627577)

            You're referring to relativistic quantum field theory, which as far as I'm aware has yet to get supporting evidence - it's simply a reasonable prediction based on the assumption that Special Relativity holds in the quantum domain, which may not be the case. SR is based on an understanding of the universe in which matter possesses locality - i.e. you can point at it an say "this thing is here", whereas one of the underlying principles of QM is that all waveforms exist at all points in the universe, albeit wi

            • It's very hard to switch light on and off quite that fast without the pulses degrading. You have a switch that can run 32 of these ports, it can do 32 times as much bandwidth as 1 port. Simple?

              Instantaneous sub-space communications over infinite distance would be freakishly strange given our current understanding of physics. It would imply that information can travel over great distances with no energy.

              • by Immerman (2627577)

                If we're sending information as single photons then pulse degradation is no longer an issue, as that's a phenomena associated with statistical wavefronts, not individual photons.

                Every time a photon reaches Earth from a distant galaxy information (that the photon was created, if nothing else) travels vast distances with no more energy than it would take to cross the room. Obviously transmitting individual photons would be immensely more efficient than a beam of light, since that pesky inverse-square law wou

                • You can always send more particles by beaming light there. Though outages are amusing. "Alpha-Centauri station? Yeah, our trasnciever is down. In 379 years there's going to be a service interruption from us, guess we'll have to work from the stock of supplied particles you're sending now, so for a little while half as much data. We'll let you know when it's back up so you know how long the outage is gonna last."

                  It takes no more energy to move a photon lightyears, but it takes YEARS to move it. If we

                  • by Immerman (2627577)

                    Who says we can create entanglement over a 10ly distance in an instant? We create the entanglement on Earth, then wait 4.4y for half the pair to reach Alpha Centauri. The information transfer might occur in an instant, but that's a completely separate issue from creating the entanglement. Now if someone can figure out how to convert 1 remotely entangled pair into 2 (or more) that would certainly improve the picture, but I don't see that there should be any assumption that it would require more energy, wha

                    • Damn, it's only 4.4LY? I thought the closest thing out there was 60-ish ... or is that the closest we can get to a nova without our planet being stripped of life?

                      It will always require as much energy to move information across space as it takes to move information across space. If it suddenly takes very little, a lot of interesting stuff happens. It's like how you have to apply a megajoule of energy to a block of steel to make it liquid molten steel; then someone says by a cheap trick of physics they ca

                    • by Immerman (2627577)

                      Yeah, A.C.'s only 4.4ly away, there's quite a few stars within 60ly. That might be the minimum safe nova distance, but seems really close for that - but maybe I'm thinking supernova.

                      Sure, heating a block of steel requires a certain minimum amount of energy, because a pool of molten steel contains considerably more energy than the block, and that energy has to come from somewhere.

                      My understanding though is that the whole energy-versus-information conversion factor is still very much in debate, is there even

                    • Regenerative braking cannot produce 100% of the energy used to accelerate. It's physically impossible. If you have a little angry demon with a molecular gate allowing hot molecules through a little door and closing it to block cold molecules, you don't get a thing with one side very hot with no energy input; the little demon must do work, and so expends energy in the process. Regenerative braking involves doing work, and so will expend energy in the process.
                    • by Immerman (2627577)

                      Maxwell's demon is an unrelated concept - basically he's trying to reverse entropy by converting two equal-temperature reservoirs into a hot and cold reservoir, from which work could then be extracted. And yes - it's not possible to do, manning the gate (or more precisely, measuring the velocity of the particles) generates more entropy than would be reversed, at least using classical physics. There was an article just the other day about some research suggesting that if the particles were entangled so tha

    • by wierd_w (1375923)

      From this? Never.

      An ansible needs to transmit information to outside its light cone.

      You can only do that in a godel spacetime, or similar spacetime. Our universe does not appear to support that.

      Also, if you create an ansible, wave goodbye to both self-determinism as a rational belief, and to causality as you know it.

  • Being from China, this has marginally more credibility than if it came out of North Korea.

    I'd certainly love to see quantum entanglement become a usable means of communication, but all of the better minds than my own I've read say that due to uncertainty principles this would be impossible.

    • Re: (Score:2, Insightful)

      by MobyDisk (75490)

      Wow, that's just plain racist. I'll let MIT's Technology Review tell me if they have reason to think the is not legitimate. Comparing Chinese research to North Korea's research is absurd. China is a modern nation with a top-tier space program.

      • by Targon (17348)

        I think you mistake a distrust of CHINA as a country with racism. The issue isn't that a Chinese person or team may have come up with it, and is more about not having much faith in press releases from certain nations. China(not Chinese people) along with North Korea are known for trying to impress those in other countries with this sort of press release when nothing exciting has happened or been discovered. That is what it all comes down to, and it does remain to be seen if this is REAL, or if it is

    • Sure. No one misleads anyone in science in the US. Please dismiss the report.

      The better minds that you have read claiming to dismiss quantum communications often dismiss *everything* because of uncertainty principles. I have an old, breadboard-based 8080 computer; I can sometimes calculate numbers in my head faster than it can provide the correct answer. Quantum communications is at level approximating the mid-1970s in personal computing. Be patient.

  • Simple really.

  • From the title, I was hoping to be able to do some nano-scale woodworking.

  • What kind of VPN throughput am I looking at here? I need new technology to replace my aging Palo Alto gateway cluster. I've begged the emissary enough already for better throughput and removal of Pah-wraiths from my network. The Cisco has yet to respond.

    Speaking of IPSEC VPN, can we get a portable configuration standard already? It's hard enough getting interoperability from devices from the same vendor (I'm looking vaguely in your direction Juniper)...

  • Quantum communication is supposed to be secure because you cannot read the message without altering it, and you get detected.

    Now if I understand the article well, we can take one photon and make two entangled photons carrying the same information, and altering one of the two photons does not alter the other one. If we have multiple quantum routers, how can a receiver know that one of them was not a man in the middle that intercepted the message?

  • ...Werner Heisenberg commented: your data may have been routed here.

It is much easier to suggest solutions when you know nothing about the problem.

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