
Scientists Achieve Direct Counterfactual Quantum Communication - mido22
http://www.sciencealert.com/scientists-have-achieved-direct-counterfactual-quantum-communication-for-the-first-time
======
politician
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...

------
ChuckMcM
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'.

------
justifier
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?

~~~
JshWright
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...

~~~
justifier
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

~~~
ajkjk
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.

~~~
skygazer
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?

~~~
gaze
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.

~~~
skygazer
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.

~~~
gaze
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

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

Am I missing something?

~~~
tbrownaw
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.

~~~
TheOtherHobbes
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.

~~~
varjack
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)

------
pavement
Abstract for paywalled PNAS paper:

[http://www.pnas.org/content/114/19/4920.abstract](http://www.pnas.org/content/114/19/4920.abstract)

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

[https://upload.wikimedia.org/wikipedia/commons/thumb/f/fb/Ei...](https://upload.wikimedia.org/wikipedia/commons/thumb/f/fb/Eight_chinese_knots.jpg/1200px-
Eight_chinese_knots.jpg)

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

------
jimmies
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.

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

~~~
dang
We detached this comment from
[https://news.ycombinator.com/item?id=14346911](https://news.ycombinator.com/item?id=14346911)
and marked it off-topic.

------
NikolaeVarius
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

~~~
gus_massa
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.

~~~
dflock
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.

~~~
semi-extrinsic
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.

