[HN Gopher] A rudimentary quantum network link between Dutch cities
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A rudimentary quantum network link between Dutch cities
Author : FrankyHollywood
Score : 147 points
Date : 2024-10-31 16:21 UTC (7 days ago)
(HTM) web link (www.tudelft.nl)
(TXT) w3m dump (www.tudelft.nl)
| 082349872349872 wrote:
| the article: https://www.science.org/doi/10.1126/sciadv.adp6442
| ziofill wrote:
| 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.
| metropolbadger wrote:
| 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.
| gatkinso wrote:
| Did you hear a cat just now?
| bawolff wrote:
| 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?
| solarkraft wrote:
| What are the classical equivalents?
| danparsonson wrote:
| Diffie-Hellman?
| dekhn wrote:
| manually distributing codebooks of pre-shared keys
| flockonus wrote:
| 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.
| ikari_pl wrote:
| 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?)
| tsimionescu wrote:
| 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.
| HuangYuSan wrote:
| 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.
| knoke wrote:
| 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/w
| iki/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!)
| fi358 wrote:
| 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?
| ko27 wrote:
| 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.
| bawolff wrote:
| > 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.
| seanhunter wrote:
| 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.
| portaouflop wrote:
| 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.
| bawolff wrote:
| 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.
| fulladder wrote:
| Just because their work is not of immediate practical
| importance does not mean it lacks value.
| ccppurcell wrote:
| 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)
| bawolff wrote:
| 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.
| ccppurcell wrote:
| 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)
| watt wrote:
| 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.
| p_l wrote:
| 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.
| bawolff wrote:
| > Safer mechanisms of distributing and establishing "root"
| keys for identify verification
|
| Except it doesn't solve the mitm problem, so its not really
| safer.
| p_l wrote:
| 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
| fsh wrote:
| 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.
| itishappy wrote:
| 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.
| vtomole wrote:
| 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.
| robblbobbl wrote:
| Cool thanks
| vtomole wrote:
| You're welcome.
| Strilanc wrote:
| (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.
| metropolbadger wrote:
| 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!
| Havoc wrote:
| 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
| pclmulqdq wrote:
| 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.
| dwnw wrote:
| 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.
| eigenket wrote:
| 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.
| dwnw wrote:
| Lots of handwaving there. Particularly with "and I can
| (locally) do stuff"
|
| Good luck with all of that.
| eigenket wrote:
| 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...
| Strilanc wrote:
| > _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_s
| wapping
|
| [3]:
| https://en.wikipedia.org/wiki/Entanglement_distillation
| andai wrote:
| 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.
| metropolbadger wrote:
| 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).
| Strilanc wrote:
| 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
| dwnw wrote:
| 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.
| robblbobbl wrote:
| Good job!
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