Hi all! I'm one of the co-authors. Honestly it's a dream to end up on HN with my research. As mentioned in the video we made, it has been a long road (6-7 years) to achieve this absolute moonshot of a project. I think we'll look back on this demonstration as the first experiment that truly made a distributed and real-world deployed quantum network. Not only did we use a (quantum) hardware platform capable of quantum processing, we also generated the entanglement in a way that it can be used in further quantum computations. In order for all this to work on a distributed network, we had to fully design and build the architecture to support that, both hard- and software. And we did it successfully!
Besides hard-working PhD students, another key ingredient that our research institute QuTech facilitated, was the collaboration with expert hardware and software engineers, allowing us to quickly transform new ideas into (deployable) products. A great show of what's possible when academia mixes with professional engineering.
But of course there was enough hacking and tinkering going on that it warrants to be on HN ;)
You can reply here if you have any questions, I'll be checking throughout the day. Thanks!
Layman here! I have no idea what's going on but I have many questions!
- Are the photons themselves carrying quantum information?
- Does the photon link result in entangled particles in Delft and Den Haag?
- Can these entangled particles be used for communication without the optical link?
Also, I tried looking this stuff up and ran into something about quantum "repeaters" and a plans for a whole quantum network. Is this research part of working towards that? How far are we now, and what steps are still missing? Thanks!
Edit: Looks like you guys built a multi-node quantum network 2 years ago! I will have to do some more reading.
- Yes and no. The photons emitted and sent through the fiber are entangled with their electron counterparts. So we send simultaneously a photon state (entangled with electron) from Delft, and a photon state (entangled with electron) from Den Haag. Those states interfere in the midpoint (Rijswijk), and upon measurement of one photon (photon now is absorbed/measured/gone) we know that the _electrons_ of the nodes in Delft and Den Haag are entangled.
- The above also answers this question: yes!
- No. They can be used to transfer a quantum state from one place to the other, for example, which _consumes_ the entanglement (one-time use only, per pair of entangled particles). However, still classical feedback signals need to propagate for that to happen, so we still need _a_ link, preferably optical (for speed and distance). Wiki has actually a great page on teleportation: https://en.wikipedia.org/wiki/Quantum_teleportation
I'll answer to a different question on repeaters later in another comment, so check back :) Indeed, multi-node quantum network was an awesome experiment. This takes it to the next level of being able to distribute entanglement over large distances and between quantum nodes that are self-sufficient (no sharing of hardware resources between nodes).
it's mostly used for crypto if I measure X here then I know the other guy will measure Y, and that is instant. But I can't force a measurement of 0 or 1 for X so as to force the Y (i.e communication).
So this means there is common knowledge of some random vector 01101010101 but nature decides the vector randomly, not humans, not communication.
You might get clever and say "aha! if I measured or not can be the communication" and that's true. The way you measure that is to see if your particle is in a superposition state or no. You shoot the entangled photon through a double slit and see if a wave-like pattern occurs, in which case we're still in a superposition and our communicator has not measured, or if it's two lines they have measured. "measured or not" thus is our "bit" that has been communicated instantly.
So the answer is kind of yes and know. At face value instant communication is not possible. Adding a quantum superposition detection device, then yes, such a device's readout may be used for Ender's game style ansible communication.
> see if your particle is in a superposition state or no. You shoot the entangled photon through a double slit and see if a wave-like pattern occurs ... "measured or not" thus is our "bit" that has been communicated instantly.
IANAQP but I'm pretty sure this is not correct. Basically everyone in the field maintains that any FTL communication is impossible.
The problem is that you almost certainly can't figure whether a given particle is entangled with some faraway particle just by looking at it; you need to look at both. "Quantum networks" rely on knowing beforehand that the particles are entangled. I think you're correct that the key advancement is common knowledge of a random (as far as we know) vector.
I think your "entanglement detector" is a misunderstanding of the double-slit experiment. (You call it a "superposition detector", but really everything is in some sort of superposition all the time.) If you fire one photon through a double slit at a sheet of photo paper, you'll always see one dot on the paper. Even though the single photon is wave-like and even interfering with itself, this is only something that becomes visibly apparent after repeating the experiment many times. So the pattern is not unique to an entangled photon, and you can't test a single photon anyway.
That's not correct; you cannot use a double-slit test to check for entanglement. Running a photon through a double-slit setup always just produces a single dot, not a any sort of pattern. To get a pattern, you need to run a bunch of photons through it and see if a fringe pattern appears [1].
(BTW, you never get a two-line pattern in a decent setup. This is an incredibly common mistake, but it's simply wrong. The interference (which produces fringes) only happens where the separate patterns from the two slits overlap, so if you want a lot of interference, you need them to overlap a lot. So in the no-interference case, you won't get two separate lines with a gap between, you'll get a single merged wash (with probably some fine structure due to diffraction within each of the slits, but that'll also be there when there is interference, on top of the two-slit interference fringes).)
You might think "ok, I'll do this with a bunch of photons, measure/not measure all of their twins, and see if the bunch of them show fringes." This is more-or-less what's done in the delayed-choice quantum eraser experiment, but it doesn't work out in a way that allows communication. What happens is that you always get the no-interference pattern. In order to see interference fringes, you need to split the individual photons' dots up based on the result of the measurement you made on their twins. Based on those measurements (if you made them), you can split the photons up into two groups, which'll have fringes with equal-and-opposite patterns (i.e. each will have bands where the other has gaps [2]).
If you didn't measure the twin photons (or made some other measurement on them instead), you can't split them up, so you won't see the fringes. But that's not because the measurements were different, it's just that you can't split them up afterward to see the fringes. And even if you did measure the twins, you can't split them up until you get a list of which twin got which result -- which can't be sent faster-than-light.
Net result: no, you can't send information via entanglement, you can only get correlation.
> You shoot the entangled photon through a double slit and see if a wave-like pattern occurs, in which case we're still in a superposition and our communicator has not measured
Wait, does this work? Are superposition detection devices theoretically possible? Got any reference with more on this?
How hard do you expect it would be to improve the heralded infidelity from 45% to 10%?
In figure 3 of the paper [1] the heralded infidelity of entanglement is reported to be around 45%. That's not good enough for computation, but it's less than 50% which means it makes purification to arbitrarily low infidelity possible. However, the conversion rates would be pretty brutal for such a high infidelity start (e.g. millions of physical pairs consumed per logical pair good enough for use in a fault tolerant computation e.g. a target logical infidelity of 1e-6 or 1e-9).
Amplification would absorb one photon and replace it with one or more new photons. Definitely not quantum.
Personally, I always wonder why point-to-point connections are called "networks". The information is not quantum at any node, even if there are multiple nodes in a system.
Then there's "quantum internet", which makes no sense at all. What are we going to do, run direct fiber from every computer to every other computer directly? You can't hop safely or anything. Don't get me started on the total bullshit that is the "quantum repeater", now we need "quantum switch" too?
We call serial port connections things like "link", "connection", etc. We typically don't call them networks until we start linking them all together with simple routing logic that doesn't inherently require access to all the unencrypted information the packets contain and such.
To me these are all just signs that the whole scheme is/was and will forever be mostly crankery.
Quantum networking is an oxymoron. It doesn't allow end-to-end encryption and in exchange gives back extremely fragile single link security properties.
I don't think it's completely clear (to me) that quantum networking is an oxymoron. I would enthusiastically agree that its very complicated and the real world use cases are incredibly limited.
As far as your routing/switching qualms go I think they are mostly addressed by entanglement swapping? Person A and person B can each make an entangled pair and send me half, and I can (locally) do stuff which leads to the halves they keep at home becoming entangled. Then they can use teleportation or whatever to do whatever they want between themselves without me knowing anything about it.
The I can locally do stuff is completely understood theoretically/mathematically. I hand waved because this isn't a forum where those technicalities are particuarly relevant.
> What are we going to do, run direct fiber from every computer to every other computer directly?
No, you don't have to do that. A quantum network would be a web of point-to-point quantum links, with paths formed by routers choosing links. Same as a classical network.
To be a bit more concrete what an operating quantum network would look like is a bunch of routers using links to build up entanglement with their neighbors. When an endpoint wants to send a message across the network, a path from source to destination would be determined and entanglement across the links of that path would be consumed to move the message across the network [1][2]. The reason it's done this way, instead of directly sending the message, is that entanglement can be cross-checked before using it [3] and quantum networks really don't like dropping packets due to the no-cloning theorem.
> We typically don't call them networks until we start linking them all together with simple routing logic
Yeah I agree that it would be more accurate for this press release to say they made a quantum link.
> To me these are all just signs that the whole scheme is/was and will forever be mostly crankery.
Don't confuse difficulty with crankery. It'll be awhile before anyone reports an experimental realization of a true quantum network, because it'll be awhile because anyone can make a quantum router. The issue is that a quantum router is for all intents and purposes a fault tolerant quantum computer, and that is its own hard challenge being worked on separately. In particular, a quantum router needs to be able to store qubits reliably for non-trivial amounts of time, and to perform reliable operations on those qubits in order to cross-check stored entanglement.
I've worked in quantum nonlinear optics during my first postdoc 12 years ago, and back then we could only dream of the efficiency of frequency conversions that are used here. So many advances in just a decade, and most of them don't even make the news.
All those incremental changes is what made my research work indeed. As we described in the paper, the margin we had on amount of signal (dependent also on the conversion efficiency!) was small, so every % of loss anywhere in this chain of photon from emission to detection mattered.
> “The distance over which we create quantum entanglement in this project, via 25 km of deployed underground fiber, is a record for quantum processors,” says Hanson. “This is the first time such quantum processors in different cities are connected.”
I know very little about quantum networking. I assume you are going beyond what they did here? How so? [1]
> Recently, as a sort of proof of potential and a first step toward functional quantum networks, a team of researchers with the Illinois‐Express Quantum Network (IEQNET) successfully deployed a long-distance quantum network between two U.S. Department of Energy (DOE) laboratories using local fiber optics.
> The experiment marked the first time that quantum-encoded photons — the particle through which quantum information is delivered — and classical signals were simultaneously delivered across a metropolitan-scale distance with an unprecedented level of synchronization.
> “To have two national labs that are 50 kilometers apart, working on quantum networks with this shared range of technical capability and expertise, is not a trivial thing,” said Panagiotis Spentzouris, head of the Quantum Science Program at Fermilab and lead researcher on the project. “You need a diverse team to attack this very difficult and complex problem.”
What is actually the usecase for "quantum internet"?
Like at most i hear about quantum key distribution, but quite frankly the classical equivalents to that are just as good if not better, so what is the actual benefit?
A quantum internet is absolutely necessary for creating a useful quantum computer, the same way the internet (LAN) is needed to create a supercomputer. A supercomputer is essentially many computers connected together. A quantum computer that solves problems we care about will be similar: https://arxiv.org/abs/2212.10609.
Still, it seems like what is needed here is more a quantum LAN, or possibly even just an on board interconnect between quantum processors. The focus on wide area quantum networks feels a bit odd.
One application we care about is using quantum computers to build high resolution telescopes https://arxiv.org/abs/1107.2939. A wide area network is required because the telescopes need to be far apart.
(1) distributed computation. If you can network two quantum computers, you essentially have one quantum computer with twice the storage. Quantum networks avoid the need to build one enormous quantum computer.
(2) easier experiments. Currently, doing a loophole free Bell inequality test is hard enough that people get PhDs for it. With a quantum network that experiment is way easier, because the network solves the hard part (distributing the entanglement). You could probably also use quantum networks for other experimental tasks, like coherently linking telescopes on separate continents, though the bandwidth and computational requirements for that would probably be a bit insane.
There are also some more out there ideas, like if stock markets contain Bell inequalities then you could use a quantum network to build up entanglement that is then consumed to win those games more often which equals $$$. But it's hard to imagine concrete scenarios that would create such an inequality, nevermind one where the expected dollars gained from the quantum strategy exceeded the cost of operating the network.
I don't know about use case but in various distributed computing models there are problems that are provably easier for quantum computers. Unlike the classical setting where the best we have is factoring where we don't know an efficient deterministic algorithm and various problems which experimentally seem to be faster for QC (and those results often don't last long as we get better at simulating quantum algorithms classically)
Well I don't really agree that quantum computers are useful! Not yet anyway.
But in (most) distributed models of computing, networks of computers share bits back and forth. The quantum distributed models have computers sharing qubits. So this seems to be a practical implementation of a system that could solve certain problems (specifically some graph labelling problems) more efficiently (specifically, in fewer message-passing rounds).
Perhaps you're confusing "internet" (a network of computers) with "world wide web" (a set of linked documents)
I could see the usecase of a local network between quantum computers in the same room. The part where i get lost is why a wide area quantum network would be useful.
A priori, a quantum network could efficiently solve e.g. leadership election or shortest path type problems. I don't think there's any evidence that they can, but any problem you might want to solve for a wide area network is potentially a use case for quantum. By the way, as I said I'm more or less a QC skeptic in the sense that I don't think we will have scalable QC doing really useful work in our lifetimes. Happy to be wrong though.
As I understand, quantum key distribution cannot be beaten by classical equivalents and they're only good or better because our current quantum computers kinda suck. So the major use case at the moment is proving the tech and developing the infrastructure. The "killer app" of the quantum internet in my mind is as simple as just sending qbits around. Currently every network call involves an observation that collapses the system wavefunction. If you're looking to actually network quantum devices (say, to run distributed quantum computations) then you need quantum infrastructure.
I'm curious too! I'd immediately understand if it allows for speed of light communication wireless, but this is clearly wired, requiring more precision engineering than usual fibre.
I guess, but benefits should be more theoretical. Like i don't think building one will give any insight into ideas for protocols. We already understand how it would work in theory and have for a long time.
Safer mechanisms of distributing and establishing "root" keys for identify verification (so you can then use them easier with normal D-H on normal internet) is one use case I recall from 1990s.
But few years ago I heard of some other interesting uses where quantum properties were used to essentially enable DWDM-like virtual circuit routing with higher capacity - though I would have to look again if it went anywhere or into scrap heap of quantum BS.
The ideas discussed in 1990s suggested a way to ensure that mitm guaranteed deviation from data transmitted. How well it would work in real life I have no idea
QKD is only safe against MITM if you have pre-shared keys between the parties. At that point you might as well use symmetric cryptography which is immune against hypothetical quantum computers and infinitely more efficient than QKD.
- security - if we use quantum entanglement/teleportation to the extent I've read about how it works, then even if you still need a fiber optic cable connecting the two parties, the data is unreadable if you're not looking at physically the same wave/photons, meaning that man in the middle attack (like the ones with bending an optic cable to break it's internal reflection) is literally impossible. The data in the middle would not be readable without the receiving end entangled device, and the other side would immediately know about the attack, because an identical signal would not be readable either, as it's not the same signal anymore.
- I think the ultimate promise is transferring data without a physical link of any kind in-between. Connect two atoms, manipulate one, read the other - like ansibles in LeGuin/O.S.Card fiction. Instant interplanetary communication (which, I think, fucks up the idea of time too?)
The first one helps with physical attacks on the wire. Not a common issue that people worry about, since there are so many boxes in between that are easier to compromise that it's rarely a significant security increase if you know the wire is perfectly secure.
The second is just wrong. It is well known and proven that it's impossible to send information via quantum entanglement. It's true that there are some interpretations of QM where the wave function of the entangled pair collapses instantly the moment one side of the pair is measured. But there is no version of QM where manipulating one side of the pair has any effect whatsoever on the other, except for measurement collapsing the quantum superposition into a random classical state.
The best classical intuition for how entanglement works is that two entangled particles are like two gloves from a pair. If you put them in boxes and separate them, when someone opens a box and finds the left glove, they instantly find out that the other person has the right glove. The difference with quantum entanglement is simply that the universe only decides which glove is which when you open the box, before that they are both in a mix of the states. This makes statistical properties measurably different if you send many pairs of gloves and look at how many times certain things match.
But there really is nothing that you can do with a pair of entangled particles that you couldn't do with the pair of gloves.
I should note for completeness that, because of the different statistical properties, there is a way to send slightly more information using entangled pairs than you can with classical particles. I believe you can send 1.5 bits of information per particle, but I don't remember the exact number. This means that a quantum internet could have higher throughput at the same transmit power, which would have some relevance for very long distance wireless communication, such as communicating with a space probe.
People have dealt with the second one in sibling comments but I somewhat doubt the first one is true when you take into account sidechannel attacks on the encoding and decoding part of the transmission.
Yes I get through quantum magic you can theoretically tell if your secret has been intercepted in the quantum state because it would cause a wave form collapse but the wave form wouldn't collapse if they were listening in to your quantum computer squeaking and buzzing and decoding those noises or timings or reading its heat signature etc, or getting your operator drunk and finding out their dog's name or partner's birthday and using it as their password, or kidnapping them and hitting them with things until they voluntarily give you their password etc. All those types of attacks would still work and still be just as undetectable as they are in classical encryption. ie all the most effective forms of attack are still just as effective in a quantum case.
I think it's a very interesting area of research but this whole idea of uncrackable codes is a stretch.
As far as In understand it (not very much) you can listen in on the transmitted keys, but the interaction can be statistically(!) measured and suspicious bits can me omitted (the wiki is quite comprehensible: https://en.wikipedia.org/wiki/Quantum_key_distribution?wprov...).
There are different protocols, some more and some less quantum and most rely on classical, encrypted channels and trusted nodes in addition to the quantum channels.
One thing is for sure: you can’t send information faster than light with this or any other kind of quantum communication as two entangled qubits are basically two RNGs that are correlated. You’d just get noise without an additional classical, not FTL, data link (please, somebody with expertise: help!)
As far as I know, they still need classical encryption methods (with something like shared secret key or public key for authentication) to detect active man in the middle attacks where the attacker prevents the parties connecting to each other and then pretending to both parties to be the other party by creating his own "messages" as if they came from the other party. Or at least to have some kind of additional trusted physical medium where it is impossible to prevent the parties communicating directly, capturing their "messages" and then sending your own modified "messages" instead -- perhaps based on some kind of timing etc.
And if you still have to rely to classical encryption methods to make sure you know the identity of the other party (to prevent active man in the middle attack), why not just use classical encryption methods for everything else as well, instead of using quantum key distribution?
You don't need "classical encryption" for quantum key distribution. With QKD you can provably detect if a MITM attack happened. With classical methods you can never be 100% sure, although how much of that matters in practice is another question.
> You don't need "classical encryption" for quantum key distribution. With QKD you can provably detect if a MITM attack happened.
This is incorrect. QKD can detect passive mitm only. It cannot detect an active mitm.
Which is the main reason its overhyped, since as cool as QKD is, you still need active mitm prevention, so you have to rely on classical crypto anyways.
To disperse some of the hype here around using this for "uncrackable" key exchange: QKD has been a product of choice for cybersecurity conmen for decades.
Hi all! I'm one of the co-authors. Honestly it's a dream to end up on HN with my research. As mentioned in the video we made, it has been a long road (6-7 years) to achieve this absolute moonshot of a project. I think we'll look back on this demonstration as the first experiment that truly made a distributed and real-world deployed quantum network. Not only did we use a (quantum) hardware platform capable of quantum processing, we also generated the entanglement in a way that it can be used in further quantum computations. In order for all this to work on a distributed network, we had to fully design and build the architecture to support that, both hard- and software. And we did it successfully!
Besides hard-working PhD students, another key ingredient that our research institute QuTech facilitated, was the collaboration with expert hardware and software engineers, allowing us to quickly transform new ideas into (deployable) products. A great show of what's possible when academia mixes with professional engineering. But of course there was enough hacking and tinkering going on that it warrants to be on HN ;)
You can reply here if you have any questions, I'll be checking throughout the day. Thanks!
Layman here! I have no idea what's going on but I have many questions!
- Are the photons themselves carrying quantum information?
- Does the photon link result in entangled particles in Delft and Den Haag?
- Can these entangled particles be used for communication without the optical link?
Also, I tried looking this stuff up and ran into something about quantum "repeaters" and a plans for a whole quantum network. Is this research part of working towards that? How far are we now, and what steps are still missing? Thanks!
Edit: Looks like you guys built a multi-node quantum network 2 years ago! I will have to do some more reading.
All good! That was me 5 years ago :)
- Yes and no. The photons emitted and sent through the fiber are entangled with their electron counterparts. So we send simultaneously a photon state (entangled with electron) from Delft, and a photon state (entangled with electron) from Den Haag. Those states interfere in the midpoint (Rijswijk), and upon measurement of one photon (photon now is absorbed/measured/gone) we know that the _electrons_ of the nodes in Delft and Den Haag are entangled.
- The above also answers this question: yes!
- No. They can be used to transfer a quantum state from one place to the other, for example, which _consumes_ the entanglement (one-time use only, per pair of entangled particles). However, still classical feedback signals need to propagate for that to happen, so we still need _a_ link, preferably optical (for speed and distance). Wiki has actually a great page on teleportation: https://en.wikipedia.org/wiki/Quantum_teleportation
I'll answer to a different question on repeaters later in another comment, so check back :) Indeed, multi-node quantum network was an awesome experiment. This takes it to the next level of being able to distribute entanglement over large distances and between quantum nodes that are self-sufficient (no sharing of hardware resources between nodes).
The article says
> which means they share a quantum connection enabling instant correlations, no matter the distance
But per your response this is not true, i.e. information transmission is still limited by the speed of light?
it's mostly used for crypto if I measure X here then I know the other guy will measure Y, and that is instant. But I can't force a measurement of 0 or 1 for X so as to force the Y (i.e communication).
So this means there is common knowledge of some random vector 01101010101 but nature decides the vector randomly, not humans, not communication.
You might get clever and say "aha! if I measured or not can be the communication" and that's true. The way you measure that is to see if your particle is in a superposition state or no. You shoot the entangled photon through a double slit and see if a wave-like pattern occurs, in which case we're still in a superposition and our communicator has not measured, or if it's two lines they have measured. "measured or not" thus is our "bit" that has been communicated instantly.
So the answer is kind of yes and know. At face value instant communication is not possible. Adding a quantum superposition detection device, then yes, such a device's readout may be used for Ender's game style ansible communication.
> see if your particle is in a superposition state or no. You shoot the entangled photon through a double slit and see if a wave-like pattern occurs ... "measured or not" thus is our "bit" that has been communicated instantly.
IANAQP but I'm pretty sure this is not correct. Basically everyone in the field maintains that any FTL communication is impossible.
The problem is that you almost certainly can't figure whether a given particle is entangled with some faraway particle just by looking at it; you need to look at both. "Quantum networks" rely on knowing beforehand that the particles are entangled. I think you're correct that the key advancement is common knowledge of a random (as far as we know) vector.
I think your "entanglement detector" is a misunderstanding of the double-slit experiment. (You call it a "superposition detector", but really everything is in some sort of superposition all the time.) If you fire one photon through a double slit at a sheet of photo paper, you'll always see one dot on the paper. Even though the single photon is wave-like and even interfering with itself, this is only something that becomes visibly apparent after repeating the experiment many times. So the pattern is not unique to an entangled photon, and you can't test a single photon anyway.
That's not correct; you cannot use a double-slit test to check for entanglement. Running a photon through a double-slit setup always just produces a single dot, not a any sort of pattern. To get a pattern, you need to run a bunch of photons through it and see if a fringe pattern appears [1].
(BTW, you never get a two-line pattern in a decent setup. This is an incredibly common mistake, but it's simply wrong. The interference (which produces fringes) only happens where the separate patterns from the two slits overlap, so if you want a lot of interference, you need them to overlap a lot. So in the no-interference case, you won't get two separate lines with a gap between, you'll get a single merged wash (with probably some fine structure due to diffraction within each of the slits, but that'll also be there when there is interference, on top of the two-slit interference fringes).)
You might think "ok, I'll do this with a bunch of photons, measure/not measure all of their twins, and see if the bunch of them show fringes." This is more-or-less what's done in the delayed-choice quantum eraser experiment, but it doesn't work out in a way that allows communication. What happens is that you always get the no-interference pattern. In order to see interference fringes, you need to split the individual photons' dots up based on the result of the measurement you made on their twins. Based on those measurements (if you made them), you can split the photons up into two groups, which'll have fringes with equal-and-opposite patterns (i.e. each will have bands where the other has gaps [2]).
If you didn't measure the twin photons (or made some other measurement on them instead), you can't split them up, so you won't see the fringes. But that's not because the measurements were different, it's just that you can't split them up afterward to see the fringes. And even if you did measure the twins, you can't split them up until you get a list of which twin got which result -- which can't be sent faster-than-light.
Net result: no, you can't send information via entanglement, you can only get correlation.
[1] https://www.researchgate.net/figure/Electron-Fringe-Pattern-...
[2] https://algassert.com/quantum/2016/01/07/Delayed-Choice-Quan...
> You shoot the entangled photon through a double slit and see if a wave-like pattern occurs, in which case we're still in a superposition and our communicator has not measured
Wait, does this work? Are superposition detection devices theoretically possible? Got any reference with more on this?
How hard do you expect it would be to improve the heralded infidelity from 45% to 10%?
In figure 3 of the paper [1] the heralded infidelity of entanglement is reported to be around 45%. That's not good enough for computation, but it's less than 50% which means it makes purification to arbitrarily low infidelity possible. However, the conversion rates would be pretty brutal for such a high infidelity start (e.g. millions of physical pairs consumed per logical pair good enough for use in a fault tolerant computation e.g. a target logical infidelity of 1e-6 or 1e-9).
1: https://arxiv.org/pdf/2404.03723#page=4
It says over fiber. I assume that has to be a straight shot point to point non-routed? Or could this deal with repeaters and routers etc
All of the quantum networking stuff is point-to-point. It's not clear to me whether fiber amplifiers are even allowed on these links.
Amplification would absorb one photon and replace it with one or more new photons. Definitely not quantum.
Personally, I always wonder why point-to-point connections are called "networks". The information is not quantum at any node, even if there are multiple nodes in a system.
Then there's "quantum internet", which makes no sense at all. What are we going to do, run direct fiber from every computer to every other computer directly? You can't hop safely or anything. Don't get me started on the total bullshit that is the "quantum repeater", now we need "quantum switch" too?
We call serial port connections things like "link", "connection", etc. We typically don't call them networks until we start linking them all together with simple routing logic that doesn't inherently require access to all the unencrypted information the packets contain and such.
To me these are all just signs that the whole scheme is/was and will forever be mostly crankery.
Quantum networking is an oxymoron. It doesn't allow end-to-end encryption and in exchange gives back extremely fragile single link security properties.
I don't think it's completely clear (to me) that quantum networking is an oxymoron. I would enthusiastically agree that its very complicated and the real world use cases are incredibly limited.
As far as your routing/switching qualms go I think they are mostly addressed by entanglement swapping? Person A and person B can each make an entangled pair and send me half, and I can (locally) do stuff which leads to the halves they keep at home becoming entangled. Then they can use teleportation or whatever to do whatever they want between themselves without me knowing anything about it.
Lots of handwaving there. Particularly with "and I can (locally) do stuff"
Good luck with all of that.
The I can locally do stuff is completely understood theoretically/mathematically. I hand waved because this isn't a forum where those technicalities are particuarly relevant.
Its been well understood since at least 1993
https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.71...
> What are we going to do, run direct fiber from every computer to every other computer directly?
No, you don't have to do that. A quantum network would be a web of point-to-point quantum links, with paths formed by routers choosing links. Same as a classical network.
To be a bit more concrete what an operating quantum network would look like is a bunch of routers using links to build up entanglement with their neighbors. When an endpoint wants to send a message across the network, a path from source to destination would be determined and entanglement across the links of that path would be consumed to move the message across the network [1][2]. The reason it's done this way, instead of directly sending the message, is that entanglement can be cross-checked before using it [3] and quantum networks really don't like dropping packets due to the no-cloning theorem.
> We typically don't call them networks until we start linking them all together with simple routing logic
Yeah I agree that it would be more accurate for this press release to say they made a quantum link.
> To me these are all just signs that the whole scheme is/was and will forever be mostly crankery.
Don't confuse difficulty with crankery. It'll be awhile before anyone reports an experimental realization of a true quantum network, because it'll be awhile because anyone can make a quantum router. The issue is that a quantum router is for all intents and purposes a fault tolerant quantum computer, and that is its own hard challenge being worked on separately. In particular, a quantum router needs to be able to store qubits reliably for non-trivial amounts of time, and to perform reliable operations on those qubits in order to cross-check stored entanglement.
[1]: https://en.wikipedia.org/wiki/Quantum_teleportation
[2]: https://en.wikipedia.org/wiki/Quantum_entanglement_swapping
[3]: https://en.wikipedia.org/wiki/Entanglement_distillation
This is all half-baked and either insecure or unrealizable in the real world we live in.
I've worked in quantum nonlinear optics during my first postdoc 12 years ago, and back then we could only dream of the efficiency of frequency conversions that are used here. So many advances in just a decade, and most of them don't even make the news.
All those incremental changes is what made my research work indeed. As we described in the paper, the margin we had on amount of signal (dependent also on the conversion efficiency!) was small, so every % of loss anywhere in this chain of photon from emission to detection mattered.
> “The distance over which we create quantum entanglement in this project, via 25 km of deployed underground fiber, is a record for quantum processors,” says Hanson. “This is the first time such quantum processors in different cities are connected.”
I know very little about quantum networking. I assume you are going beyond what they did here? How so? [1]
> Recently, as a sort of proof of potential and a first step toward functional quantum networks, a team of researchers with the Illinois‐Express Quantum Network (IEQNET) successfully deployed a long-distance quantum network between two U.S. Department of Energy (DOE) laboratories using local fiber optics.
> The experiment marked the first time that quantum-encoded photons — the particle through which quantum information is delivered — and classical signals were simultaneously delivered across a metropolitan-scale distance with an unprecedented level of synchronization.
> “To have two national labs that are 50 kilometers apart, working on quantum networks with this shared range of technical capability and expertise, is not a trivial thing,” said Panagiotis Spentzouris, head of the Quantum Science Program at Fermilab and lead researcher on the project. “You need a diverse team to attack this very difficult and complex problem.”
[1] https://www.anl.gov/article/quantum-network-between-two-nati...
the article: https://www.science.org/doi/10.1126/sciadv.adp6442
What is actually the usecase for "quantum internet"?
Like at most i hear about quantum key distribution, but quite frankly the classical equivalents to that are just as good if not better, so what is the actual benefit?
A quantum internet is absolutely necessary for creating a useful quantum computer, the same way the internet (LAN) is needed to create a supercomputer. A supercomputer is essentially many computers connected together. A quantum computer that solves problems we care about will be similar: https://arxiv.org/abs/2212.10609.
Thanks, that was really intrresting.
Still, it seems like what is needed here is more a quantum LAN, or possibly even just an on board interconnect between quantum processors. The focus on wide area quantum networks feels a bit odd.
One application we care about is using quantum computers to build high resolution telescopes https://arxiv.org/abs/1107.2939. A wide area network is required because the telescopes need to be far apart.
Cool thanks
You're welcome.
(1) distributed computation. If you can network two quantum computers, you essentially have one quantum computer with twice the storage. Quantum networks avoid the need to build one enormous quantum computer.
(2) easier experiments. Currently, doing a loophole free Bell inequality test is hard enough that people get PhDs for it. With a quantum network that experiment is way easier, because the network solves the hard part (distributing the entanglement). You could probably also use quantum networks for other experimental tasks, like coherently linking telescopes on separate continents, though the bandwidth and computational requirements for that would probably be a bit insane.
There are also some more out there ideas, like if stock markets contain Bell inequalities then you could use a quantum network to build up entanglement that is then consumed to win those games more often which equals $$$. But it's hard to imagine concrete scenarios that would create such an inequality, nevermind one where the expected dollars gained from the quantum strategy exceeded the cost of operating the network.
I don't know about use case but in various distributed computing models there are problems that are provably easier for quantum computers. Unlike the classical setting where the best we have is factoring where we don't know an efficient deterministic algorithm and various problems which experimentally seem to be faster for QC (and those results often don't last long as we get better at simulating quantum algorithms classically)
I agree that quantum computers are useful. Its quantum internet that seems pointless.
As far as i am aware, none of the problems faster on a QC are helped in anyway by quantum internet.
Well I don't really agree that quantum computers are useful! Not yet anyway.
But in (most) distributed models of computing, networks of computers share bits back and forth. The quantum distributed models have computers sharing qubits. So this seems to be a practical implementation of a system that could solve certain problems (specifically some graph labelling problems) more efficiently (specifically, in fewer message-passing rounds).
Perhaps you're confusing "internet" (a network of computers) with "world wide web" (a set of linked documents)
I could see the usecase of a local network between quantum computers in the same room. The part where i get lost is why a wide area quantum network would be useful.
A priori, a quantum network could efficiently solve e.g. leadership election or shortest path type problems. I don't think there's any evidence that they can, but any problem you might want to solve for a wide area network is potentially a use case for quantum. By the way, as I said I'm more or less a QC skeptic in the sense that I don't think we will have scalable QC doing really useful work in our lifetimes. Happy to be wrong though.
As I understand, quantum key distribution cannot be beaten by classical equivalents and they're only good or better because our current quantum computers kinda suck. So the major use case at the moment is proving the tech and developing the infrastructure. The "killer app" of the quantum internet in my mind is as simple as just sending qbits around. Currently every network call involves an observation that collapses the system wavefunction. If you're looking to actually network quantum devices (say, to run distributed quantum computations) then you need quantum infrastructure.
I'm curious too! I'd immediately understand if it allows for speed of light communication wireless, but this is clearly wired, requiring more precision engineering than usual fibre.
What do you mean by "speed of light communication wireless"? Wireless signals (WiFi or similar) are already speed of light.
There is no obvious benefit yet, they are just researching for the sake of it.
I think over time they will discover a benefit but the hype is obviously not warranted.
I guess, but benefits should be more theoretical. Like i don't think building one will give any insight into ideas for protocols. We already understand how it would work in theory and have for a long time.
Just because their work is not of immediate practical importance does not mean it lacks value.
Safer mechanisms of distributing and establishing "root" keys for identify verification (so you can then use them easier with normal D-H on normal internet) is one use case I recall from 1990s.
But few years ago I heard of some other interesting uses where quantum properties were used to essentially enable DWDM-like virtual circuit routing with higher capacity - though I would have to look again if it went anywhere or into scrap heap of quantum BS.
> Safer mechanisms of distributing and establishing "root" keys for identify verification
Except it doesn't solve the mitm problem, so its not really safer.
The ideas discussed in 1990s suggested a way to ensure that mitm guaranteed deviation from data transmitted. How well it would work in real life I have no idea
QKD is only safe against MITM if you have pre-shared keys between the parties. At that point you might as well use symmetric cryptography which is immune against hypothetical quantum computers and infinitely more efficient than QKD.
What are the classical equivalents?
Diffie-Hellman?
manually distributing codebooks of pre-shared keys
isn't it too early to try to draw a bottom line for this type of research?
from my perspective this is fascinating area of physics that we need to know more about and will improve our understanding of fundamental physics.
I'd prefer @ziofill to answer, but I think:
- security - if we use quantum entanglement/teleportation to the extent I've read about how it works, then even if you still need a fiber optic cable connecting the two parties, the data is unreadable if you're not looking at physically the same wave/photons, meaning that man in the middle attack (like the ones with bending an optic cable to break it's internal reflection) is literally impossible. The data in the middle would not be readable without the receiving end entangled device, and the other side would immediately know about the attack, because an identical signal would not be readable either, as it's not the same signal anymore.
- I think the ultimate promise is transferring data without a physical link of any kind in-between. Connect two atoms, manipulate one, read the other - like ansibles in LeGuin/O.S.Card fiction. Instant interplanetary communication (which, I think, fucks up the idea of time too?)
The first one helps with physical attacks on the wire. Not a common issue that people worry about, since there are so many boxes in between that are easier to compromise that it's rarely a significant security increase if you know the wire is perfectly secure.
The second is just wrong. It is well known and proven that it's impossible to send information via quantum entanglement. It's true that there are some interpretations of QM where the wave function of the entangled pair collapses instantly the moment one side of the pair is measured. But there is no version of QM where manipulating one side of the pair has any effect whatsoever on the other, except for measurement collapsing the quantum superposition into a random classical state.
The best classical intuition for how entanglement works is that two entangled particles are like two gloves from a pair. If you put them in boxes and separate them, when someone opens a box and finds the left glove, they instantly find out that the other person has the right glove. The difference with quantum entanglement is simply that the universe only decides which glove is which when you open the box, before that they are both in a mix of the states. This makes statistical properties measurably different if you send many pairs of gloves and look at how many times certain things match.
But there really is nothing that you can do with a pair of entangled particles that you couldn't do with the pair of gloves.
I should note for completeness that, because of the different statistical properties, there is a way to send slightly more information using entangled pairs than you can with classical particles. I believe you can send 1.5 bits of information per particle, but I don't remember the exact number. This means that a quantum internet could have higher throughput at the same transmit power, which would have some relevance for very long distance wireless communication, such as communicating with a space probe.
People have dealt with the second one in sibling comments but I somewhat doubt the first one is true when you take into account sidechannel attacks on the encoding and decoding part of the transmission.
Yes I get through quantum magic you can theoretically tell if your secret has been intercepted in the quantum state because it would cause a wave form collapse but the wave form wouldn't collapse if they were listening in to your quantum computer squeaking and buzzing and decoding those noises or timings or reading its heat signature etc, or getting your operator drunk and finding out their dog's name or partner's birthday and using it as their password, or kidnapping them and hitting them with things until they voluntarily give you their password etc. All those types of attacks would still work and still be just as undetectable as they are in classical encryption. ie all the most effective forms of attack are still just as effective in a quantum case.
I think it's a very interesting area of research but this whole idea of uncrackable codes is a stretch.
As far as In understand it (not very much) you can listen in on the transmitted keys, but the interaction can be statistically(!) measured and suspicious bits can me omitted (the wiki is quite comprehensible: https://en.wikipedia.org/wiki/Quantum_key_distribution?wprov...). There are different protocols, some more and some less quantum and most rely on classical, encrypted channels and trusted nodes in addition to the quantum channels.
One thing is for sure: you can’t send information faster than light with this or any other kind of quantum communication as two entangled qubits are basically two RNGs that are correlated. You’d just get noise without an additional classical, not FTL, data link (please, somebody with expertise: help!)
As far as I know, they still need classical encryption methods (with something like shared secret key or public key for authentication) to detect active man in the middle attacks where the attacker prevents the parties connecting to each other and then pretending to both parties to be the other party by creating his own "messages" as if they came from the other party. Or at least to have some kind of additional trusted physical medium where it is impossible to prevent the parties communicating directly, capturing their "messages" and then sending your own modified "messages" instead -- perhaps based on some kind of timing etc.
And if you still have to rely to classical encryption methods to make sure you know the identity of the other party (to prevent active man in the middle attack), why not just use classical encryption methods for everything else as well, instead of using quantum key distribution?
You don't need "classical encryption" for quantum key distribution. With QKD you can provably detect if a MITM attack happened. With classical methods you can never be 100% sure, although how much of that matters in practice is another question.
> You don't need "classical encryption" for quantum key distribution. With QKD you can provably detect if a MITM attack happened.
This is incorrect. QKD can detect passive mitm only. It cannot detect an active mitm.
Which is the main reason its overhyped, since as cool as QKD is, you still need active mitm prevention, so you have to rely on classical crypto anyways.
No, this does not work. You can both read the same random data (which can be used for generating encryption keys), but not transfer any data.
To disperse some of the hype here around using this for "uncrackable" key exchange: QKD has been a product of choice for cybersecurity conmen for decades.
https://www.nsa.gov/Cybersecurity/Quantum-Key-Distribution-Q...
https://www.ncsc.gov.uk/whitepaper/quantum-security-technolo...
https://en.wikipedia.org/wiki/Snake_oil_(cryptography)
Stick with TLS. If you really think quantum computers are a threat to anything, use a hybrid-PQC key exchange.
My honest professional opinion is a cryptographically-relevant quantum computer will never exist, making classic cryptography superior in every case.
Good job!
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Did you hear a cat just now?