Scientists Achieve Direct Counterfactual Quantum Communication For The First Time (sciencealert.com) 117
schwit1 shares an article from ScienceAlert:
Quantum communication is a strange beast, but one of the weirdest proposed forms of it is called counterfactual communication -- a type of quantum communication where no particles travel between two recipients. Theoretical physicists have long proposed that such a form of communication would be possible, but now, for the first time, researchers have been able to experimentally achieve it -- transferring a black and white bitmap image from one location to another without sending any physical particles... 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.
It's different than quantum entanglement (which Einstein described as "spooky action at a distance.") The article describes it as "a pretty cool demonstration of just how bizarre and unexplored the quantum world is."
It's different than quantum entanglement (which Einstein described as "spooky action at a distance.") The article describes it as "a pretty cool demonstration of just how bizarre and unexplored the quantum world is."
counterfactual communication (Score:1)
Oh please! We've been doing that since the invention of marriage, no wait, I mean politics...
Re: (Score:3)
Only if you don't open it.
So... (Score:5, Insightful)
How is this different than radio?
If I'm 11000 miles from someone's radio transmitter, waves of magnetism induce electron movement in my local loop antenna (this description applies only to loop antennas.) The only particles -- electrons -- I'm dealing with are local. The particle movement is not induced by electrons that travelled from the source to my antenna. Magnetism isn't carried by particles. Right? Because it goes right through non-ferrous solid objects.
Light is just radio at a really high frequency, as far I understand it. Which may not be all that far. :)
Anyway, shine a light, induce particle movement at the receiver by detecting the waves...
Sounds like radio. What am I missing? There must be something, or this wouldn't be news.
--[not a physicist]
Re: (Score:2)
> I am pretty sure the summary left out the most important bit, which would make it all make sense.
Are we still waiting for that bit... or did my ADHD kick in mid sentence?
Re:So... (Score:5, Interesting)
"How is this different than radio?"
Signal strength. If implemented in the real world it would be harder to jam or disrupt. We already have used tight beam laser communications but they are line of sight and susceptible to interference by any particles between the source and target. It seems this new attempt at something else would provide better performance without the line of sight or environmental obstructions getting in the way. If any of this type of technology becomes practical look for it to show up in the military technology basket. This new technology also opens the door for advancements in encryption making interception and deciphering the content much more difficult if not impossible at this time.
Re: (Score:2)
This does not jive with the explanation of the quantum bomb detector [wikipedia.org]. Your whole communication apparatus would need to be in a sensitive interferometer, built so that certain photons only have two possible paths. The entire counterfactual finding relies on the premise that if a photon lands on a certain detector (D), both the following are true: it could have been received at another "B", and was not.
Re: So... (Score:1)
Re:So... (Score:5, Interesting)
Radio waves are photons too. Light is just photons that happen to have the right frequency for our eyes to pick up. Whenever electrons are changing magnetic fields that act on other electrons, deep down at the quantum mechanical level it turns out to actually be an interchange of photons.
In this latest experiment, no photons or any other kind of particles were exchanged between emitter and receiver. So it really is quite different.
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Photons are simply particles. However, just like any other particle, they travel as waves. Whenever a photon (or any other kind of particle) is emitted, it travels through space as a wave function until it is measured somewhere (or some other event causes the wave function to collapse). Then, the particle will be detected or not, depending on the probability given by the wave function at that point in spacetime.
So saying that no particles are involved, only waves, does not make much sense. Waves are not som
Re:So... (Score:5, Interesting)
In this latest experiment, no photons or any other kind of particles were exchanged between emitter and receiver. So it really is quite different.
That's not actually quite true. Photons are sent (and in fact photon counters are used to detect the signal). However, the information itself isn't encoded in the photons, it's encoded in the phase of the photons. The abstract uses the comparison to holography: in normal photography, only the amplitude of the light is relevant. In holography, the phase of a laser is used to encode information as well (specifically, the 3D depth of the target) in addition to the amplitude. This technique encodes all of the information into the phase alone, and none of it stays in the amplitude.
TFA is, to put in bluntly, wrong. It claims
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.
But light is photons, and photons are light. You can't encode information in light without sending photons: it's like saying you talk to someone over the phone using words, but without using sound. It's just absurd. Of course, you can communicate over the phone using sound without using words, which is roughly analogous to what the scientists actually did.
Re: So... (Score:1)
Re: So... (Score:1)
Re:So... (Score:5, Informative)
You are misunderstanding quantum counterfactual communications.
Quantum counterfactual communications uses the principle of interaction-free measurement. Although the information was phase encoded in photons, the information is transmitted in photons that are not actually sent to the receiver. Strangely (and this is hard to understand) photons are sent with some probability to the receiver, so it's possible that the receiver receives some photons, but those photons actually sent don't actually encode the information, but the information is conveyed by the photons that don't actually get sent. That way any photons that incidentally get sent can be "observed" without consequence of wave function collapse of the information.
This is similar effect to the quantum bomb detector [wikipedia.org] thought experiment.
One interesting multi-verse interpretation of the multi-path bomb detectors is that in the universes where the photon took the path where the bomb went off aren't our universe, so we get to experience the consequence of the photon taking the other path. Similarly in this quantum counterfactual communication, we get to experience the consequences of the photons that were not transmitted.
Re: (Score:2)
Yes, and every single detected photon in the universe is a counterfactual to all the other paths the photon could have taken. Normally, these paths are numerous and unknowable, but if you build a machine just right, you can restrict the paths so much that there are just a few, and witnessing one path can eliminate some others as possibilities, and also prove the existence of a separate but coherent path.
Re:So... (Score:4, Interesting)
Yes, and every single detected photon in the universe is a counterfactual to all the other paths the photon could have taken. Normally, these paths are numerous and unknowable, but if you build a machine just right, you can restrict the paths so much that there are just a few, and witnessing one path can eliminate some others as possibilities, and also prove the existence of a separate but coherent path.
Although restricting the paths is one way to do this (with the quantum bomb detector), I believe the proposed quantum counterfactual communicaton technique actually uses the Quantum Zeno Effect [wikipedia.org]. Instead of restricting the paths of a photon, the Quantum Zeno effect restricts the time-evolution of the photon temporarily preventing quantum decoherence.
Basically a watched pot never boils on (quantum) steroids.
This Quantum Zeno effect has also been proposed as the mechanism for long spin coherence lifetimes of radical-ion pairs that birds likely use for Magnetoreception [arxiv.org]
An answer (Score:5, Informative)
You can define a particle as something that has energy - either rest energy as mass, or energy in motion as a photon.
Most of the time you need some sort of transfer of energy to transfer information. A photon is sent from one place to another, it interacts with a sensor, and information is exchanged.
One interpretation of this effect is that the photon itself doesn't travel down the path, it's the *probability* of the photon that travels down the path. When a particle is emitted, the universe takes the particle and puts it on a shelf somewhere (outside the universe) and sends out an instantaneous probability wave. As the wave evolves, the universe checks it for interactions with things along the path, and when the probability indicates an interaction it replaces the probability wave with the particle.
The probability wave takes all possible paths from the source to the destination, including non-straight paths. Most of the time most of the paths cancel out, leaving one path (the straight line) or two (beamsplitter mirror) or a few more, depending on the configuration.
I haven't found a non-paywalled version of the frikkin' paper yet, so I can't comment on what they're doing, but it seems like they are using the probability that the particle might be at the destination to affect particles at the destination without actually sending the particle.
There was an article in Scientific American that talked about taking a picture of Medusa without receiving any photons from Medusa. The presence of a photon in a cavity will alter the resonance frequency of a cavity which can be detected (IIRC - the article was many years ago).
If what the paper claims is true(*), it means that information can be transferred from one location to another without the transfer of energy, which is a very interesting philosophical statement.
(*) Many times in physics, especially QM, experimental outcomes turn out to be different than expected, so it's good to do the experiments. (Viz. Popper's experiment.)
Further answer (Score:5, Informative)
I've found the paper.
Using beamsplitters, Alice sets up one probability path that goes out to Bob and back. Bob can either insert a mirror, reflecting the probability path back to Alice, or not, making the probability path end there. Bob's mirror will change the phase of the Alice's photon in a way that can be detected by Alice, even though the photon doesn't actually go out to Bob.
A good simple example of what they're doing is the quantum bomb detector [wikipedia.org], where you can determine whether a bomb attached to a single-photon detector would explode if given a photon... without actually giving it a photon.
In the bomb example, you are getting information about the bomb without actually transferring energy to or from the bomb.
The experiment in the paper is somewhat similar.
Re: Further answer (Score:1)
Re: (Score:2)
In the bomb example, you are getting information about the bomb without actually transferring energy to or from the bomb.
As I understand it (and I'm not fully confident that I do), you sometimes get information about the bomb without transferring energy to or from the bomb.
link to paper (Score:1)
https://sci-hub.cc/10.1073/pnas.1614560114
i think it's the one, took 1 minute to find its DOI and look that up on scihub
Respect for SciHub (Score:2)
https://sci-hub.cc/10.1073/pnas.1614560114
i think it's the one, took 1 minute to find its DOI and look that up on scihub
1) I took more than 1 minute to look for other versions first, out of respect for SciHub. SciHub is a great resource, and I don't like to use their resources if it can be avoided.
2) I didn't post the SciHub link, out of respect for SciHub. SciHub is a great resource, and I don't want to use up their resources by publicly posting their links.
3) Pointing out things obvious to you in a snarky way is elitist.
4) Nothing is easier and more pathetic than being a critic.
Re: An answer (Score:1)
Re: (Score:1)
Doesn't the radio antenna receive photons as particles though?
I know camera sensors do (thus the noise in low light, not enough photons to override the randomness).
More bewilderment on my part (Score:2)
There are two basic ways to build yourself a radio antenna.
One responds to electrostatics; this, generally speaking, is electron, or photon activation - electrons in the antenna move because the applied charge across the antenna varies. This is ambient electron pressure varying as a function of the radio signal. This results in push-pull down the antenna cable, and it's amplified at the receiver, etc.
The other responds to magnetic fields. Not ambient electron pressure. A loop antenna is a classic example of
Re: (Score:1)
Either one can induce the other. But they are not the same.
Relativity (which is just Lorentz transformers, something inherent to the Maxwell's equations) shows that electric and magnetic fields are interchangeable by simply changing your reference frame. Some graduate level homework problems about particle motion in complicated fields amount to just changing to a frame where the magnetic or electric field disappear, and you have a simpler problem to deal with... but still the same situation.
Unless photons ignore solid objects
Photons don't ignore solid objects, but are quite capable of going through
Some (cough) light at last (Score:2)
Thank you. Although I have no great depth in the areas you're describing, you did provide a coherent framework that gives me some idea what might be happening. And you provided enough touchstones for me to fumble through learning more. Very much appreciated.
I got the idea that electrons = photons from camera sensor descriptions in the popular press. No doubt there was some level of error there, starting with me and possibly extending further. I've parked that idea. :)
Re: So... (Score:1)
This is based on https://en.m.wikipedia.org/wiki/Quantum_Zeno_effect
For someone familiar with computing, you can think of it as a covert channel over a particle entanglement.
Contrary to regular communication channels, there is no contiguous particle movement (e.g: photons for light) from source to destination (for sound, it would be multiple particles transmitting the wave, but there is a contiguous movement).
Re: (Score:1)
Re: (Score:2)
What am I missing? There must be something, or this wouldn't be news.
That something you are missing is their new found grant money. Redefine light as non-particles, profit! This is how quantum theory works.
Re: (Score:2)
You've...entirely misunderstood what they've done. XD
Re: (Score:2)
The waves of magnetism are actually photons, which are considered massless particles.
Re: (Score:2)
Sounds like radio. What am I missing?
It sounds like maybe they didn't actually send an electromagnetic wave. They just set up a device that could send such a wave then didn't turn it on and used quantum magic to determine what would have happened if they had turned it on.
Or maybe they did something else entirely.
In case it's not obvious, I'm not a physicist either.
Re: (Score:2)
Photons are only particles when they interact with something. Here, they're using interaction-free measurement, communicating by modulating the phase of the wave function in a way that's detectable without collapsing it, and thus no energy transfer or 'particle'.
Re: (Score:2)
The problem is that what a quantum physicist refers to as a "wave function" does not directly relate to the EM waves themselves. What's being referred to is that the specific properties of a particle (location, momentum, time, etc) is not deterministic, but rather probabilistic. And when you plot this function, the result looks remarkably "wave-like" in that the probabilities are not continuous, but rather they have highs and lows, or peaks and troughs.
https://en.wikipedia.org/wiki/... [wikipedia.org]
Enter Heisenburg and
No FTL from this (Score:5, Informative)
Re: No FTL from this (Score:1)
Re:No FTL from this (Score:4, Informative)
It's a reasonable cautinary comment to make, obviously based on the observation that some people may assume that FTL limitations are based on the limitations of particle transmission, and lacking any particle transmission, those limits might not come into play. Because not everyone reading this site have taken courses in physics.
Re: (Score:2)
Re: (Score:2)
All hail Shannon.
Re: (Score:2)
All hail Turing, you mean. But the government wasn't going to publish the stuff kept secret during the war under the name of some embarrassing gay guy, even if it was his work, so Shannon gets the glory. Or so I've heard.
Re: No FTL from this (Score:2)
Maybe he is. Maybe he isn't. We won't know unless we measure
Re: (Score:1)
Careful to not crash the universe! (Score:3)
Given the universally observable incompetence, the simulation environment running this universe is probably running on something in the same class as Windows XP. Create too many exceptions like the one in this experiment (ordinary things are clearly not simulated at this detail...) and you may just crash the whole thing. That may be bad.
Re: (Score:2)
The last back up they did was around 65 million years ago (12:00 this morning, laptop time).
Re: (Score:2)
The computer running the simulation we live in will one day soon be infected by ransomware. Will our creators pay the ransom, or just wipe the system and start over? We have to provide enough value to our creators to justify them paying up.
Re: they transmitted... (Score:1)
Re: (Score:2)
It's both hardcore AND softcore, until you measure it.
Classical channel? (Score:2)
Does it require one? Or can I use it to get internet on my submarine?
Re: (Score:1)
It doesn't need the classical channel.
But you will be stuck with a bundle including the christian broadcasting, shopping and the "fishing shit"*.
* reference for the British TV comedy geeks
Re: (Score:2)
Never mind your submarine. Maybe now we can get optical broadband to our neighborhood without having to dig up the sidewalks and bury fiber.
If this does in fact work, it's going to be buried so deep by the three letter agencies that we'll never see it. Imagine me having essentially what are a pair of optical modems linked by quantum entanglement. One in my house and one in a rack at an ISP in a country with the power to say "Fuck you!" to the NSA. And nothing they can tap between the two.
Re:a country with the power to say Fuck you NSA (Score:2)
Nothing new here? (Score:2)
How is this any different from modulating the light with e.g. coloured filters to send signals?
It seems to me people have already been doing this for centuries.
Exactly that (Score:3)
How is this any different from modulating the light with e.g. coloured filters to send signals?
It seems to me people have already been doing this for centuries.
it's exactly like modulating light using coloured filters.
Except that there is no light.
Re: (Score:3)
OK, so they're just modulating dark with coloured filters.
From TFA (Score:2)
"artefacts that couldn't surprise direct light shined on them."
Some needs to be severely reprimanded for this.
Re: (Score:2)
Some needs to be severely reprimanded for this.
...eh? ;)
Re:3*10^8 m/s. (Score:5, Informative)
Is there any idea why Lightspeed == Radio speed ?
Yes, it's because radio is light.
Re: (Score:1)
An antenna is not a lantern.
An antenna is the filament of a radio lightbulb.
Re: (Score:2)
Electrons don't move at the speed of light. They have mass (albeit quite a small, but non-zero, amount) therefore they can not move at light speed or they would have infinite mass (and take an infinite amount of energy to get up to speed).
Photons, not electrons, are the carrier of electromagnetic radiation. They move at the speed of light.
Antennas and lanterns both emit photons. Lanterns just happen to emit photons in a range of energy levels that our eyes are sensitive to. Antennas emit photons at a differ
Re: (Score:2)
Electrons don't move at the speed of light.
True, but an electrical signal generally can travel a significant faction of c [wikipedia.org], with ladder line achieving 95-99% of c.
An imperfect model would be the same way sound can travel very quickly in a block of solid steel (~5700 m/s) while an individual atom of steel doesn't really move at all.
Re: (Score:2)
Radio utilizes an electron as the messenger particle.
It's helpful to stop reading the above comment at this point, and start watching out for all the electricity flying through the air into your radio.
Radio is electromagnetic radiation. So is light. Here's a handy chart [wikipedia.org]
.
Re: (Score:2)
I get what you're trying to say, but that's an oversimplification. The word light [wikipedia.org] does not mean "anything in the entire electromagnetic spectrum" by any standard definition.
Lightspeed == radio speed because they are both forms of electromagnetic radiation (which travels at the speed of light).
Re: (Score:2)
There is no standard definition of the term, and if there was, Wikipedia would not be the definitive source for it. In fact, the Wikipedia page says this:
The word usually refers to visible light
In physics, the term light sometimes refers to electromagnetic radiation of any wavelength, whether visible or not
Re: (Score:2)
Yes, that's exactly my point. And any sampling of dictionary definitions will confirm this.
Explain please kthxbye (Score:2)
The article is woefully short on details. What, exactly, do the senders of a message do, in this case?
And what is a "quantum channel"?
Re: Explain please kthxbye (Score:1)
TFA is counterfactual (Score:2)
"The basic idea is this - someone wants to send an image to Alice using only light (which acts as a wave, not a particle, in the quantum realm)."
Nonsense. Photons have properties of both.
https://en.wikipedia.org/wiki/... [wikipedia.org]
"researchers have been able to experimentally achieve it - transferring a black and white bitmap image from one location to another without sending any physical particles."
If you pretend a photon is only a particle which it is not then you can make pretend statements such as the above. And
Re: TFA is counterfactual (Score:1)
Either wrong or just incomprehensible (Score:2)
I can't decide whether the summary is wrong or just incomprehensible. I think it's wrong. Of course, it *may* be accurately reporting on the original article... but skimming the article I think that it's (the linked article) incomprehensible rather than just wrong. (It may also be wrong, but that's not something I can check.)
The article seems to imply that a quantum channel can transmit information without transmitting particles. (paraphrase "If the channel transmits a particle then it is discarded".)
Re: Either wrong or just incomprehensible (Score:1)
Uh, I'm not sure I understand. Is this the same (Score:2)
thing as all the "alternative factual" communications I've been seeing so much of recently?
Yall motherfuckers need some patterns (Score:1)
I've seen this before... (Score:1)
Communication using "pilot wave theory" (Score:1)
Re: someone else said practically the same thing (Score:2)