10 ms·

The quantum internet has arrived (and it hasn’t)

90 points by cpheinrich 9y ago

crenellated 9y ago
Ugh. Images like this are why no one should ever pay attention to fluff magazine articles about quantum anything: https://media.nature.com/w800/magazine-assets/d41586-018-01835-3/d41586-018-01835-3_15461638.jpg https://media.nature.com/w800/magazine-assets/d41586-018-018... The person who created that picture had no clue what the diagram is supposed to represent. They obviously created the infographic based on a conversation with someone who probably also doesn’t completely understand what their talking about. Why articles like this must be written at all is what gets me. Someone out there wants this topic to have an article published, and they just don’t really care if the information it presents lacks accuracy.
- dang 9y ago
  It sounds like you know enough about the topic to post a comment that doesn't break this HN guideline: Please don't post shallow dismissals, especially of other people's work. A good critical comment is one that teaches us something. In the future, could you please do that instead? Bilious dismissals degrade discussion; explaining a more correct view elevates it. https://news.ycombinator.com/newsguidelines.html https://news.ycombinator.com/newsguidelines.html
- krastanov 9y ago
  I work in the field, on my way to a doctorate, and I do not see anything bothersome with the infographic. It is well made and factual.
tomonl 9y ago
Stephanie Wehner also taught a great course on quantum cryptography. https://ocw.tudelft.nl/courses/quantum-cryptography/ https://ocw.tudelft.nl/courses/quantum-cryptography/
- marius_k 9y ago
  She can explain the topic really well. I attended her talk at SHA2017[0]. [0] https://media.ccc.de/v/SHA2017-361-invitation_to_help_build_quantum_internet https://media.ccc.de/v/SHA2017-361-invitation_to_help_build_...
mratzloff 9y ago
No, it hasn't. Also, re: this image[0], I thought entanglement couldn't be used to send information? Isn't this complete nonsense? [0] https://media.nature.com/w800/magazine-assets/d41586-018-01835-3/d41586-018-01835-3_15461638.jpg https://media.nature.com/w800/magazine-assets/d41586-018-018...
- tomonl 9y ago
  The image is correct. The information is sent over a classical channel, not using entanglement.
  - krastanov 9y ago
    While the image is correct, your statement would be a bit misleading to novices: You can not transfer the state of the qubit over a classical channel. You need both a classical channel and entanglement. Or in other words: a bit can be send over a classical communication channel (by copying it), but to transmit a qubit (which can not be copied due to its quantum nature), you either need to carry the physical qubit over, or use entanglement together with classical communication.
    - IntronExon 9y ago
      The essence of the issue for many, who seem to equate entanglement with FTL is that a classical channel is required. Without that, you’re just sending noise over your quantum channel. Plus we get to keep cause and effect ordered, as a little bonus.
- red75prime 9y ago
  The last section tells that you need to transmit classical information to make sense of entangled particle measurement. Entanglement serves as a secure channel. If you have two entangled coins, you know that the second coin came up heads, if your coin came up tails. You can't transmit information that way, because if you'll force your coin to land heads, you'll break entanglement. But you can use the results of coin flips as a cipher.
7ero 9y ago
I'm a bit confused by the process of entangling photons emitted by two distinct qubits, wouldn't entangling those photons affect the state of the two original distinct qubits? Or is that simply how entanglement works?
- krastanov 9y ago
  Very naively, the following happens: Qubit A is entangled with Photon A. Qubit B is entangled with Photon B. Photon A and Photon B are measured together in way that does not permit distinguishing the two photons (this is where the magic happens) and destroyed. This results in Qubit A and Qubit B now being entangled.
  - kenning 9y ago
    Thanks, this helps a lot
hartator 9y ago
> quantum particles [...] has been used for years to enhance data encryption. As an entropy source or more?
- krastanov 9y ago
  No, it is way more interesting than that. With entangled particles together with a public unencrypted classical communication channel you can create a protocol to exchange information securely. That protocol does not rely on any computational complexity assumptions, rather only on the assumption that the laws of quantum mechanics are correct. There are some caveats, but it is still an amazing construction. https://en.wikipedia.org/wiki/Quantum_key_distribution https://en.wikipedia.org/wiki/Quantum_key_distribution https://en.wikipedia.org/wiki/BB84 https://en.wikipedia.org/wiki/BB84
SCAQTony 9y ago
A cat walks into a bar... or did he?
tristanj 9y ago
Do we really need a quantum internet though? Our current non-quantum encryption system honestly works very well. Symmetric encryption is statistically unbreakable at large enough key sizes. Using a brute-force attack on a 256-bit AES key, it would take billions of years to crack, even with a quantum computer. Given a large enough key size (1024-bits), it would take longer than the heat death of the universe to crack such a key. For key exchange, quantum encryption is definitely better, but how much better is it than switching to a quantum resistant key exchange algorithm? And switching to quantum encryption would require a complete internet infrastructure overhaul, meaning fiber optics everywhere, all new routers (would packet routing still work?), new cell towers, and no more copper lines for internet. Is this complete architectural overhaul worth it, just to decrease the chance of being hacked from 1/2^256, to 0? To me the benefits seem marginal. It reminds me of flying cars: yes it's the future, yes they work, yes we can do it, but is it practical?
- cpheinrich 9y ago
  I think the idea is that if you want to transmit quantum information you need a quantum internet. There are many cases where you would want to transmit quantum information besides using it as an encryption scheme. For example, if a scientist wants to run a quantum simulation in the cloud, and then they want the quantum state to be communicated back to their local quantum machine _without_ collapsing the wave function, then you would need some kind of quantum link to do so. If you want to send it through the classical internet you would have to collapse the wave function and send classical information.
- krastanov 9y ago
  I completely agree that while quantum key exchange is amazing, in practical terms it might not be necessary for great security. However, creating a long range quantum network (as a supplement to the classical internet), would provide amazing new capabilities (plenty of which we probably have not thought of yet). I am particularly excited about using it to link up sensors (telescopes) so that we can surpass the diffraction limit of classical sensors.
  - space_fountain 9y ago
walrus01 9y ago
One of the huge problems of requiring lossless photon transmission through fiber: This will break all currently known approaches to DWDM. It is not economical for inter-city transport between ISPs to require its own dark strand pair, no WDM of any type, in most scenarios. There's a reason why people want to be able to do things like 100/200/400GbE coherent frequencies in a 80-channel DWDM bandplan.
EGreg 9y ago
Can this enable FTL communication? https://www.livescience.com/59810-quantum-teleportation-record-shattered.html https://www.livescience.com/59810-quantum-teleportation-reco...
- tomonl 9y ago
  No, a classical connection (e.g. the internet) is needed for quantum teleportation. This classical connection won't be faster than light.
JepZ 9y ago
That woman on the title picture somehow reminded me of Stargate's fictional character Jeanie Miller :D https://78.media.tumblr.com/tumblr_lifvvogP0H1qh5nggo1_500.jpg https://78.media.tumblr.com/tumblr_lifvvogP0H1qh5nggo1_500.j...

90 points by cpheinrich 9y ago

Ugh. Images like this are why no one should ever pay attention to fluff magazine articles about quantum anything: https://media.nature.com/w800/magazine-assets/d41586-018-01835-3/d41586-018-01835-3_15461638.jpg https://media.nature.com/w800/magazine-assets/d41586-018-018... The person who created that picture had no clue what the diagram is supposed to represent. They obviously created the infographic based on a conversation with someone who probably also doesn’t completely understand what their talking about. Why articles like this must be written at all is what gets me. Someone out there wants this topic to have an article published, and they just don’t really care if the information it presents lacks accuracy.

dang 9y ago
It sounds like you know enough about the topic to post a comment that doesn't break this HN guideline: Please don't post shallow dismissals, especially of other people's work. A good critical comment is one that teaches us something. In the future, could you please do that instead? Bilious dismissals degrade discussion; explaining a more correct view elevates it. https://news.ycombinator.com/newsguidelines.html https://news.ycombinator.com/newsguidelines.html
krastanov 9y ago
I work in the field, on my way to a doctorate, and I do not see anything bothersome with the infographic. It is well made and factual.

tomonl 9y ago

Stephanie Wehner also taught a great course on quantum cryptography. https://ocw.tudelft.nl/courses/quantum-cryptography/ https://ocw.tudelft.nl/courses/quantum-cryptography/

marius_k 9y ago
She can explain the topic really well. I attended her talk at SHA2017[0]. [0] https://media.ccc.de/v/SHA2017-361-invitation_to_help_build_quantum_internet https://media.ccc.de/v/SHA2017-361-invitation_to_help_build_...

mratzloff 9y ago

No, it hasn't. Also, re: this image[0], I thought entanglement couldn't be used to send information? Isn't this complete nonsense? [0] https://media.nature.com/w800/magazine-assets/d41586-018-01835-3/d41586-018-01835-3_15461638.jpg https://media.nature.com/w800/magazine-assets/d41586-018-018...

tomonl 9y ago
The image is correct. The information is sent over a classical channel, not using entanglement.
- krastanov 9y ago
  While the image is correct, your statement would be a bit misleading to novices: You can not transfer the state of the qubit over a classical channel. You need both a classical channel and entanglement. Or in other words: a bit can be send over a classical communication channel (by copying it), but to transmit a qubit (which can not be copied due to its quantum nature), you either need to carry the physical qubit over, or use entanglement together with classical communication.
  - IntronExon 9y ago
    The essence of the issue for many, who seem to equate entanglement with FTL is that a classical channel is required. Without that, you’re just sending noise over your quantum channel. Plus we get to keep cause and effect ordered, as a little bonus.
red75prime 9y ago
The last section tells that you need to transmit classical information to make sense of entangled particle measurement. Entanglement serves as a secure channel. If you have two entangled coins, you know that the second coin came up heads, if your coin came up tails. You can't transmit information that way, because if you'll force your coin to land heads, you'll break entanglement. But you can use the results of coin flips as a cipher.

7ero 9y ago

I'm a bit confused by the process of entangling photons emitted by two distinct qubits, wouldn't entangling those photons affect the state of the two original distinct qubits? Or is that simply how entanglement works?

krastanov 9y ago
Very naively, the following happens: Qubit A is entangled with Photon A. Qubit B is entangled with Photon B. Photon A and Photon B are measured together in way that does not permit distinguishing the two photons (this is where the magic happens) and destroyed. This results in Qubit A and Qubit B now being entangled.
- kenning 9y ago
  Thanks, this helps a lot

hartator 9y ago

> quantum particles [...] has been used for years to enhance data encryption. As an entropy source or more?

krastanov 9y ago
No, it is way more interesting than that. With entangled particles together with a public unencrypted classical communication channel you can create a protocol to exchange information securely. That protocol does not rely on any computational complexity assumptions, rather only on the assumption that the laws of quantum mechanics are correct. There are some caveats, but it is still an amazing construction. https://en.wikipedia.org/wiki/Quantum_key_distribution https://en.wikipedia.org/wiki/Quantum_key_distribution https://en.wikipedia.org/wiki/BB84 https://en.wikipedia.org/wiki/BB84

SCAQTony 9y ago

A cat walks into a bar... or did he?

tristanj 9y ago

Do we really need a quantum internet though? Our current non-quantum encryption system honestly works very well. Symmetric encryption is statistically unbreakable at large enough key sizes. Using a brute-force attack on a 256-bit AES key, it would take billions of years to crack, even with a quantum computer. Given a large enough key size (1024-bits), it would take longer than the heat death of the universe to crack such a key. For key exchange, quantum encryption is definitely better, but how much better is it than switching to a quantum resistant key exchange algorithm? And switching to quantum encryption would require a complete internet infrastructure overhaul, meaning fiber optics everywhere, all new routers (would packet routing still work?), new cell towers, and no more copper lines for internet. Is this complete architectural overhaul worth it, just to decrease the chance of being hacked from 1/2^256, to 0? To me the benefits seem marginal. It reminds me of flying cars: yes it's the future, yes they work, yes we can do it, but is it practical?

cpheinrich 9y ago
I think the idea is that if you want to transmit quantum information you need a quantum internet. There are many cases where you would want to transmit quantum information besides using it as an encryption scheme. For example, if a scientist wants to run a quantum simulation in the cloud, and then they want the quantum state to be communicated back to their local quantum machine _without_ collapsing the wave function, then you would need some kind of quantum link to do so. If you want to send it through the classical internet you would have to collapse the wave function and send classical information.
krastanov 9y ago
I completely agree that while quantum key exchange is amazing, in practical terms it might not be necessary for great security. However, creating a long range quantum network (as a supplement to the classical internet), would provide amazing new capabilities (plenty of which we probably have not thought of yet). I am particularly excited about using it to link up sensors (telescopes) so that we can surpass the diffraction limit of classical sensors.
- space_fountain 9y ago

walrus01 9y ago

One of the huge problems of requiring lossless photon transmission through fiber: This will break all currently known approaches to DWDM. It is not economical for inter-city transport between ISPs to require its own dark strand pair, no WDM of any type, in most scenarios. There's a reason why people want to be able to do things like 100/200/400GbE coherent frequencies in a 80-channel DWDM bandplan.

EGreg 9y ago

Can this enable FTL communication? https://www.livescience.com/59810-quantum-teleportation-record-shattered.html https://www.livescience.com/59810-quantum-teleportation-reco...

tomonl 9y ago
No, a classical connection (e.g. the internet) is needed for quantum teleportation. This classical connection won't be faster than light.

JepZ 9y ago

That woman on the title picture somehow reminded me of Stargate's fictional character Jeanie Miller :D https://78.media.tumblr.com/tumblr_lifvvogP0H1qh5nggo1_500.jpg https://78.media.tumblr.com/tumblr_lifvvogP0H1qh5nggo1_500.j...