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Communications Technology

How To Encode 2.05 Bits Per Photon, By Using Twisted Light 91

Thorfinn.au writes Researchers at the University of Rochester and their collaborators have developed a way to transfer 2.05 bits per photon by using "twisted light." [Abstract here.]This remarkable achievement is possible because the researchers used the orbital angular momentum of the photons to encode information, rather than the more commonly used polarization of light. The new approach doubles the 1 bit per photon that is possible with current systems that rely on light polarization and could help increase the efficiency of quantum cryptography systems.
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How To Encode 2.05 Bits Per Photon, By Using Twisted Light

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  • by Anonymous Coward on Saturday March 21, 2015 @07:32PM (#49310435)

    How do you have a fraction of a bit?

    • by Anonymous Coward on Saturday March 21, 2015 @07:36PM (#49310455)
      205 bits per 100 photons.
    • by sribe ( 304414 )

      Well, suppose that with each photon you can transmit 1 of 3 values: 0, 1, or 2. How many bits per photon would that be?

      So, yes, you may well have been the only one wondering ;-)

      • by dwywit ( 1109409 )

        I'm wondering how the conventional logic at either end of the process would manage to cope with three values. Can hardware be designed to work with more than on/off one/zero logic, i.e. perhaps one reaction for zero volts, another reaction for 2 volts, and a third reaction for 4 volts.

        Of course, I am not a hardware designer.

        • by sribe ( 304414 ) on Saturday March 21, 2015 @11:15PM (#49311329)

          I'm wondering how the conventional logic at either end of the process would manage to cope with three values. Can hardware be designed to work with more than on/off one/zero logic, i.e. perhaps one reaction for zero volts, another reaction for 2 volts, and a third reaction for 4 volts.

          Dude, analog modems have been coding multiple bits per transition for DECADES, using both amplitude and phase to encode multiple values per transition. As do cable modems, DSL, and so on. Just about every transmission encoding method for the past 30 years...

          In the example of 3 values, you get 0, 1 or 2. Then on the next transition, multiply by 3 and add 0, 1, or 2. And so on. That's simplified, because in fact there's typically more states than values, and mapping of states -> values involves techniques to mitigate the effects of interference.

        • by sjames ( 1099 )

          The same way a sound card does it. Each sample yields a value (for example) from 0 to 255 encoded in binary.

          Or, for example, an 8 line GPIO can be encoded into a single byte.

          For a less neat example, perhaps a sample can be one of 3 levels, 00, 01, or 10. Those can be packed into a byte and quickly translated, either through a combination of masking adding and multiplying into an accumulator or a table lookup where some table indices would indicate illegal states. You could call it binary coded base 3, analo

        • by colinwb ( 827584 )

          A 1958 Soviet Union computer [wikipedia.org] used ternary logic.

          And according to this [wikipedia.org] and this [computer-museum.ru] Donald Knuth thinks that sometime "flip-flop" will be replaced by "flip-flap-flop". Also this [earltcampbell.com].

    • by Anonymous Coward

      Not all the data is contained within 1 photo. It is spread across many.

      For example in order to understand the words I wrote you had to read the whole sentence. Data is spread out across the whole container in addition to the sub parts.

      • Not all the data is contained within 1 photo. It is spread across many.

        Only when you have more than 1,000 words.

    • Inflation.
    • @Anonymous Coward: "How do you have a fraction of a bit?"

      I dunno, I do know my brain hurts :)

      "Here we describe a proof-of-principle experiment that indicates the feasibility of high-dimensional QKD [iop.org] based on the transverse structure of the light field allowing for the transfer of more than 1 bit per photon."
    • not sure for the first half, but (data >> 0.5) & 0.5 gets the 2nd half
    • Use Imperial bits instead of Metric bits and you're done.

  • Is this something you can shove down a fiber optic line?

    Seems like that would be awesome for telecom stuff if it would work.

    • Re: (Score:2, Informative)

      by Anonymous Coward

      Infinite-capacity wireless vortex beams carry 2.5 terabits per second [extremetech.com]

      American and Israeli researchers have used twisted vortex beams to transmit data at 2.5 terabits per second. As far as we can discern, this is the fastest wireless network ever created — by some margin. This technique is likely to be used in the next few years to vastly increase the throughput of both wireless and fiber-optic networks.

      These twisted signals use orbital angular momentum (OAM) to cram much more data into a single stream

      • by ArcadeMan ( 2766669 ) on Saturday March 21, 2015 @08:55PM (#49310837)

        American and Israeli researchers have used twisted vortex beams to transmit data at 2.5 terabits per second.

        Egon Spengler: There's something very important I forgot to tell you.
        Peter Venkman: What?
        Spengler: Don't cross the streams.
        Venkman: Why?
        Spengler: It would be bad.
        Venkman: I'm fuzzy on the whole good/bad thing. What do you mean, "bad"?
        Spengler: Try to imagine all life as you know it stopping instantaneously and every molecule in your body exploding at the speed of light.
        Ray Stantz: Total protonic reversal!
        Venkman: Right. That's bad. Okay. All right. Important safety tip. Thanks, Egon.

  • What I'm wondering is whether the limit is 2.71828 or so.
    • What I'm wondering is whether the limit is 2.71828 or so.

      e is just the highest anyone can count, because if you start reciting it you will never get to 3.

  • by Anonymous Coward

    Am I only one who finds the concept of using twisted beams of light to encode information overwhelmingly obvious?

  • by Anonymous Coward on Saturday March 21, 2015 @08:05PM (#49310623)

    An Anonymous Coward at Slashdot have developed a way of transfer 4 bits per photon by using "different colors". This remarkable achievement is possible because the anonymous coward used the wavelength of the photons to encode information, rather than the more commonly used polarization of light. During transmission Alice sends a photon of one of 16 predefined wavelengths (colors) and using a prism Bob detects the color and thus obtains 4 bits of information. The new approach quadruples the 1 bit per photon that is possible with current systems that rely on light polarization and could help increase the efficiency of quantum cryptography systems.

  • Oh Come On! (Score:2, Flamebait)

    Anybody else read this and think, "Oh come on ... the physicists are just getting silly and making up shit now."

    I'm still waiting for somebody to synthesize this whole field and make it halfway possible to visualize.

    • by Kjella ( 173770 )

      I'm still waiting for somebody to synthesize this whole field and make it halfway possible to visualize.

      You'll probably be waiting a very long time. Reality doesn't make the math easy, for example if you want to describe water flowing down a stream good luck on all the non-linearity in the eddies and currents. Or the way turbulence acts in air resistance, it's messy. There's no real reason to think it'll get easier on the particle/wave level, in fact it ends up working in even more messed up ways you wouldn't imagine on the macro scale. But hey you can hope, I'd advise against holding your breath while you wa

      • Fluid turbulence is actually well understood and very easy to visualize. Yes, direct simulation of turbulence is very computationally expensive, but good mathematical models for the effect of turbulence in flows have been around for a while and are used in CFD modeling in many industries.

        I can actually see turbulence; if I just go down to the river or look up at the sky, there it is. It's complex, but it obeys simple rules and you can actually develop a physical intuition about turbulence.

        Not so with quantu

  • I have a small setup on my desktop that encodes 8 bit per photon. It is called a spectrum analyzer together with a laser. It could probably encode a lot more if it was optimized for that, but lacks the sensitivity.

    • by Anonymous Coward

      Err... a spectrum analyzer won't do anything with 1 photon. Nor will a optical power meter...

    • That's great, but totally worthless for quantum cryptography. Quantum cryptography relies on quantum properties of the photons (spin/polarization/orbital angular momentum), so that someone in the middle who makes a measurement will disturb the system. Using spectral encoding or modulation or any one of a dozen other ways of encoding data will result in a much higher data rate than the one given in TFA, but almost all of those are worthless for quantum cryptography.

      • by mysidia ( 191772 )

        Quantum crypto. Isn't of much use to the industry.... compared to say....... getting 100 Terabits of second worth of data down a single fiber optic cable.

        • Quantum crypto. Isn't of much use to the industry.... compared to say....... getting 100 Terabits of second worth of data down a single fiber optic cable.

          Bulk data transmission and quantum crypto have somewhat different target industries (though anyone using quantum cryptography is probably using it to secure high-speed fiber lines). Quantum crypto is used (as in used, right now, today) for quantum key distribution in environments that need/want extremely high security so they can communicate extremely securely over regular (but fast) channels.

  • We've had OAMM encoding and transmission of data for a while, usually coupled with quadrature amplitude modulation.

    I've heard of slashdot being slow, but by at least THREE YEARS? That's got to be a new record.

    Maybe you guys should start reading Nature Photonics.

  • The Deep Space Network has been transmitting 2.5 bits per photon for the past 30+ years. http://what-when-how.com/space... [what-when-how.com]

    How do these researchers not know that already?

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