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> Steinberg, who agrees with the statistical view of the situation, argues that a single tunneled particle can’t convey information. A signal requires detail an

> Steinberg, who agrees with the statistical view of the situation, argues that a single tunneled particle can’t convey information. A signal requires detail and structure, and any attempt to send a detailed signal will always be faster sent through the air than through an unreliable barrier. This argument doesn't make a lot of sense to me. One particle arriving can signal information that some event has occurred at the source. Re: structure/complexity I imagine you could use different elements (and maybe spin too?) to form several bits.

deleted 6y ago
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lisper 6y ago
The devil is in the details. I haven't done the math (I'm probably not capable of actually doing the math) but my bet is that it is not possible to set up a tunneling barrier that does not also effect the spin component of the wave function. My further bet is that it will turn out that the uncertainty introduced into the spin component by the tunneling barrier is just enough to produce a no-communications theorem for tunneling just as there is one for entanglement. I'll even place a third bet that there's a Ph.D. thesis (if not a Nobel prize) at the bottom of that rabbit hole.
h0l0cube 6y ago
I think it's a matter of a low signal-to-noise ratio. So if you send one bit, but there's a low probability the other side will receive it, you'll need so much redundancy and error correction to achieve the same bandwidth as a regular signal, that it ends up being at least the same transmission rate.
lacker 6y ago
I think your intuition is correct and that Steinberg is agreeing with you here. Steinberg is just saying that a single particle alone cannot generate a causality paradox. But it still isn't obvious why you couldn't use this effect with multiple bits and some error correct to send signals faster than light. Looking at the paper being discussed here - https://iopscience.iop.org/article/10.1088/1367-2630/abb515/meta https://iopscience.iop.org/article/10.1088/1367-2630/abb515/... - the authors also don't seem to have an explanation. One final caveat worth noting is that our results do not definitively prove that an ensemble of free particles will always be a preferable method of transmitting a signal to an ensemble of tunneled particles. It is our intention to include a discussion of this in a follow-up paper. This is basically the scenario you're talking about, forming several bits out of different particles and using them in conjunction to send information faster than light. The researchers aren't sure why this wouldn't happen in their model.
- h0l0cube 6y ago
  Given the probabilistic nature of quantum effects I doubt there's a reliable way to tunnel particles. If a tunnelling event happens with low frequency, the receiver would need a side-channel or some redundancy to be sure it had received a signal. But it will be interesting to see what comes up in their follow-up paper.
  - enkid 6y ago
    That's why you use multiple. It doesn't matter how unreliable, if it only works on in a million times, you send two million. Still the same concept.
    - h0l0cube 6y ago
      Of course, but in using multiple I wager we would end up with a transmission rate the same or worse than without tunnelling. Might be wrong, but I'll defer to the actual experts on this one.
    - andrewljohnson 6y ago
      Is there an upper bound on how noisy the signal can be and still work?
  - dogma1138 6y ago
    We exploit quantum tunneling in many applications, you are posting from a device that wouldn’t work if there was no reliable way to exploit quantum tunneling.
    - h0l0cube 6y ago
      I'd like to know more about that. I know transistor design requires mitigating quantum tunnelling as it unpredictably alters the flow of elections. I doubt there's a way to make tunnelling sufficiently reliable enough to permit a higher transfer rate, but willing to stand corrected.
akvadrako 6y ago
Yeah, it does not seem to matter how unreliable it is. If you send some some particles every time event occurs and occasionally they are received, even a single detection now gives the receiver information: that event occurred. If the particles were sent FTL, you can now setup the standard causality paradoxes.
- WJW 6y ago
  All of the usual caveats from information theory apply though. In particular, the noisiness of the channel plays a huge part in Shannons equation for information capacity. In this case in particular, if you receive no particles you know that the event either did not happen _or_ it did happen and you failed to detect the particle. If you do receive a particle you know that either the event happened at least once _or_ it did not happen and you have a false positive from your detector _or_ there was a particle but it was introduced by quantum noise. To make sure what actually happened you would need more signal, more particles per transmitted bit. However, it is entirely possible that this reduction in effective bit rate will slow down actual bit rates back down to "normal" subluminal speeds.
  - drdeca 6y ago
    But isn't whether it is superluminal a question of the latency, not the bandwidth? (Where, the bit rate, bits/second, would, I think, be a measure of bandwidth. I could be wrong.)

deleted 6y ago

[deleted]

lisper 6y ago

The devil is in the details. I haven't done the math (I'm probably not capable of actually doing the math) but my bet is that it is not possible to set up a tunneling barrier that does not also effect the spin component of the wave function. My further bet is that it will turn out that the uncertainty introduced into the spin component by the tunneling barrier is just enough to produce a no-communications theorem for tunneling just as there is one for entanglement. I'll even place a third bet that there's a Ph.D. thesis (if not a Nobel prize) at the bottom of that rabbit hole.

h0l0cube 6y ago

I think it's a matter of a low signal-to-noise ratio. So if you send one bit, but there's a low probability the other side will receive it, you'll need so much redundancy and error correction to achieve the same bandwidth as a regular signal, that it ends up being at least the same transmission rate.

lacker 6y ago

I think your intuition is correct and that Steinberg is agreeing with you here. Steinberg is just saying that a single particle alone cannot generate a causality paradox. But it still isn't obvious why you couldn't use this effect with multiple bits and some error correct to send signals faster than light. Looking at the paper being discussed here - https://iopscience.iop.org/article/10.1088/1367-2630/abb515/meta https://iopscience.iop.org/article/10.1088/1367-2630/abb515/... - the authors also don't seem to have an explanation. One final caveat worth noting is that our results do not definitively prove that an ensemble of free particles will always be a preferable method of transmitting a signal to an ensemble of tunneled particles. It is our intention to include a discussion of this in a follow-up paper. This is basically the scenario you're talking about, forming several bits out of different particles and using them in conjunction to send information faster than light. The researchers aren't sure why this wouldn't happen in their model.

h0l0cube 6y ago
Given the probabilistic nature of quantum effects I doubt there's a reliable way to tunnel particles. If a tunnelling event happens with low frequency, the receiver would need a side-channel or some redundancy to be sure it had received a signal. But it will be interesting to see what comes up in their follow-up paper.
- enkid 6y ago
  That's why you use multiple. It doesn't matter how unreliable, if it only works on in a million times, you send two million. Still the same concept.
  - h0l0cube 6y ago
    Of course, but in using multiple I wager we would end up with a transmission rate the same or worse than without tunnelling. Might be wrong, but I'll defer to the actual experts on this one.
  - andrewljohnson 6y ago
    Is there an upper bound on how noisy the signal can be and still work?
- dogma1138 6y ago
  We exploit quantum tunneling in many applications, you are posting from a device that wouldn’t work if there was no reliable way to exploit quantum tunneling.
  - h0l0cube 6y ago
    I'd like to know more about that. I know transistor design requires mitigating quantum tunnelling as it unpredictably alters the flow of elections. I doubt there's a way to make tunnelling sufficiently reliable enough to permit a higher transfer rate, but willing to stand corrected.

akvadrako 6y ago

Yeah, it does not seem to matter how unreliable it is. If you send some some particles every time event occurs and occasionally they are received, even a single detection now gives the receiver information: that event occurred. If the particles were sent FTL, you can now setup the standard causality paradoxes.

WJW 6y ago
All of the usual caveats from information theory apply though. In particular, the noisiness of the channel plays a huge part in Shannons equation for information capacity. In this case in particular, if you receive no particles you know that the event either did not happen _or_ it did happen and you failed to detect the particle. If you do receive a particle you know that either the event happened at least once _or_ it did not happen and you have a false positive from your detector _or_ there was a particle but it was introduced by quantum noise. To make sure what actually happened you would need more signal, more particles per transmitted bit. However, it is entirely possible that this reduction in effective bit rate will slow down actual bit rates back down to "normal" subluminal speeds.
- drdeca 6y ago
  But isn't whether it is superluminal a question of the latency, not the bandwidth? (Where, the bit rate, bits/second, would, I think, be a measure of bandwidth. I could be wrong.)