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Scientists Achieve Direct Counterfactual Quantum Communication (sciencealert.com)
88 points by mido22 191 days ago | hide | past | web | 26 comments | favorite

Does it require entanglement? No.

> Direct counterfactual quantum communication on the other hands relies on something other than quantum entanglement. Instead, it uses a phenomenon called the quantum Zeno effect.

Does it violate the speed of light? No.

> It works based on the fact that, in the quantum world, all light particles can be fully described by wave functions, rather than as particles. So by embedding messages in light the researchers were able to transmit this message without ever directly sending a particle.

Is this a sleight of hand? I don't know... ("New system of angular motion doesn't require radians! Uses 'degrees' instead.")

> ...all light particles can be fully described by wave functions, rather than as particles...

Wow, I remember reading a paper on this as a theory about 10 years ago in Scientific American. At the time I don't recall the paper actually having a way to do the experiment, it was in the category of 'look what the math says is possible'.

from the abstract

> Intuition from our everyday lives gives rise to the belief that information exchanged between remote parties is carried by physical particles. Surprisingly, in a recent theoretical study .. quantum mechanics was found to allow for communication, even without the actual transmission of physical particles.

ok, does this also mean that communication is free from restraints that particles suffer.. as in would this allow faster than light communication?

The speed of light isn't a property inherent to physical particles. It is far more fundamental than that.

Check out the PBS Space Time channel. They have a number of excellent episodes on the speed of light, causality, etc...

yeah, i'm sorry i should have been more clear

what i am interested in is:

i understand that solely utilising quantum entanglement, a ftl phenomenon, one is unable to communicate classical information but does this method utilise the zeno effect to afford this communication by controlling when to cease and reinstate the systems evolution?

two parties with entangled particles within quantum systems agree on a baud rate and the transmitter alters the systems evolution until it takes on a desirable state then arrest the evolution until the next scheduled modulation, then evolve the state to the next desired expression, wait for the next modulation, and on and on

effectively the information transfer would adhere to causality, the observer would be subject to the baud rate, but the distance traveled between the parties could be greater than one that light could travel within that baud rate

Er. Quantum entanglement is not a faster than light phenomenon. Or, at least, describing it as such is rather pointless. It's no more 'faster than light' than 'realizing something about a faraway place' is.

Isn't collapse of the probability wave instantaneous across the arbitrary distance between entangled particles, from the frame of the measurement, in violation of relativity, and isn't that what Einstein disliked?

The wave function isn't really this thing that physically exists but is really a data structure which exists only in your head that captures the information you have about a quantum system. So yeah collapse is instantaneous, but that's just because you can update something in your head instantly because you learned something about something that happened far away.

I don't know that that's true. I'm by no means, even remotely, an expert. But it sounds like you've got a "hidden variables" take on it; that you're suggesting the probability wave is our statistical prediction of a systems state limited by our ignorance, which is what Einstein believed, and has been since contradicted by physical experiment showing violation of Bell's inequality? Am I mistaken? Feel free to correct me.

Ah that's not what I'm saying but it's subtle. Access to hidden variables, if they existed, would allow you to predict a measurement outcome. I'm not saying that. I'm saying the wave function is a tool that allows you to write down all the correlations. In other words, the wave function is a tool that allows you to reproduce all the probability distributions

It has to have been possible for the information to have traveled between the parties normally. In this case, it has to have been possible that a photon would have traveled between the two. Since the information couldn't have arrived FTL normally due to the everyday causality problems, it also couldn't have passed through this channel FTL.

They still transmitted light, they just called it a wave instead of a particle.

Am I missing something?

I have no idea if this is relevant to this experiment, but it illustrates how a path that had no light sent down it can affect light that went down another path: https://en.wikipedia.org/wiki/Elitzur%E2%80%93Vaidman_bomb_t...

Yes, you're missing whatever's hidden behind the journal paywall.

It's been way to long since my one quantum physics class, but looking at the pretty pictures I think they got their photon to interfere destructively with itself over the entire length of the transmission channel between a pair of beam splitters.

Which I don't think is possible with ordinary waves (say in water), which I suppose is probably what the big deal is.

If you go Full Copenhagen and start thinking about QM as a calculus of probability densities in physical systems it begins to make a lot more sense than trying to think about it as an impossibly weird version of Newtonian mechanics for waves+particles+wtf.

It means you can stop playing "Where's the photon?" and accept that these experiments are doing spatially distributed probabilistic computing.

In this view there is no photon - there's only a map of possible photon-like event positions distributed in spacetime, and one or more end-points tuned to pick up photon-like events by sampling the map at specific spacetime locations.

The weird part is the way that interactions between the map distributions and the end-points are completely unintuitive, and you can do neat tricks like constraining probabilities by repeatedly connecting to an end-point, and creating dead areas where the probability of an event is zero but which don't "block" events around them.

That just emphasises that the Newtonian-ish view is the wrong model. The right view is still TBD, but it seems to be some kind of holistic summary view that somehow - no one can even begin to guess how - creates a map by integrating over all possible interactions.

This is not what we're used to, but discovering that reality doesn't do what we expect is the point of science, so that's not a bad thing.

Please stop waving your hands. I prefer the deBroglie-Bohm interpretation where you have both a particle and a wave. Changing the shape of the wave by changing site B setup changes where the particle ends up, even if the particle does not leave site A. (However, for this experiment to work, there should be a chance for the particle to travel from A to B, otherwise the pilot wave won't travel either)

Abstract for paywalled PNAS paper:


The image transmitted was a monochrome bitmap graphic of a Chinese knot:


...no resolution noted in the abstract, but probably small and pixelated, since it was serialized as photomultiplier clicks.

If you want to read the paper, type in your address bar sci-hub.cc and a slash, and then paste the DOI after the slash.

We are receiving a wireless telegraph! It is from Marconi. He wants us to get off his lawn.

We detached this comment from https://news.ycombinator.com/item?id=14346911 and marked it off-topic.

We upvoted this comment, because it made us laugh.

Title: Scientists Achieve Direct Counterfactual Quantum Communication For The First Time.

Article: "The results will now need to be verified by external researchers to make sure what the researchers saw was a true example of counterfactual quantum communication."

Okay then

This is usual. I don't know why they explained it here. [1]

This result was published in a peer review journal. It means that two or three experts read the article and found no evident flaw and think that it has enough details to make the experiment in another laboratory [2]. They didn't go to the laboratory and unbolted every piece to double check the setup, or make a copy in their own laboratory to check the experiment. So until two or three more laboratories try this and a few variations, this is still doubtful, but there is a good chance that this is true.

[2] Usually the papers don't have enough information. You have to guess and email the authors and cross your fingers to reproduce the result.

[1] My guess is that they explained this because the result is very unintuitive.

As you sort of imply in your second footnote, "has enough details to make the experiment in another laboratory" often _isn't_ a requirement to pass peer review, sadly.

It's frequently a loose requirement; trouble is to know how much information is necessary to replicate, you typically have to do the actual replication (and iterate with authors over details). Not to mention that journals tend to dislike overly long papers.

That's probably why it's included in "fakenews" category on https://github.com/StevenBlack/hosts

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