5 ms·

First demonstration of quantum teleportation over busy Internet cables

35 points by m-hodges 2y ago

iandanforth 2y ago
The use of "Internet" in the title and article is deceptive. They did not send data over the Internet, they sent conventional optical data over a 30 mile spool of fiber and quantum entangled photons on an unused wavelength over the same cable in a laboratory setting.
- ko27 2y ago
  It's not deceptive. The whole point of the study was to figure out a way to transfer quantum information through active Internet cables, and not empty optical cables.
  - fsh 2y ago
    I find the wording highly deceptive. The main feature making the internet globally scalable is not that it goes through fibers, but that it uses package routing. Nobody knows how to do this with qubits, so quantum communication doesn't scale at all. Instead, the community started doing these publicity stunts with very limited applicability.
    - swores 2y ago
      Their title is specific in saying "internet cables", not the internet. It seems fair to me that this is one step on the journey, that figuring out going through cables comes before figuring out routing between cables. It's a press release for a specific research paper, not a product release marketed to consumers. (Though it's possible the researchers themselves agree with you & iandanforth more than with me & ko27, as the title of the actual research paper itself doesn't use this wording; it's "Quantum teleportation coexisting with classical communications in optical fiber".)
inkcapmushroom 2y ago
Is anyone able to explain to me how this demonstrates "information without direct transmission" when a direct 30km fiber line is needed to transmit the data, and how you can call it teleportation when it's "limited by the speed of light"? Not doubting they did something special but I couldn't tell from the article what exactly it was that they did which is unique from standard fiber transmission (other than they received a single photon using an atypical frequency).
- ko27 2y ago
  This is basic QM "spooky action at a distance" stuff. Quantum information is teleported instantaneously, however to make use of that information, you actually need to transfer classical information over regular channels. That doesn't mean it's not useful, see for example the way QKD works: https://en.wikipedia.org/wiki/Quantum_key_distribution https://en.wikipedia.org/wiki/Quantum_key_distribution
- eppp 2y ago
  I know almost nothing about this but lay understand is this: the state of a photon can possibly be encoded with a vast amount of information, instead of transmitting that information encoded into light, they transmitted the state of entangled photons and thusly recreated the information on the third photon.
- jerf 2y ago
  Being generous, they say that "direct transmission" is not necessary because they are not "directly" transmitting a "1" or a "0", but instead an entanglement. I agree that, as is fairly usual for this field, this is poorly phrased, probably poorly understood by the writer, and prone to misinterpretation. There absolutely certainly is a "direct transmission" of some photons to achieve the effect, irreducibly so. You can't move entanglement around without some sort of carrier, photons in this case (as they are the most convenient for this task for much the same reasons they're quite convenient for conventional transmissions as well). Quantum teleportation is not related to speed. Quantum teleportation is when you entangle two particles, A and B, and then you take the entanglement on B and send the entanglement itself to some distant particle C. A and C are then entangled in exactly the same way that A and B were (this is the "teleportation"), and B no longer is. This is an intrinsically destructive operation on the original A/B entanglement. The requirement to be "quantum teleportation" is merely than the entanglement is transferred, regardless of speed; if you could send an entangled particle via the slowest shipping Fedex has and transfer the entanglement days later, that would still be quantum teleportation. However, it's all very delicate and that's not practical or possible, so photons are one of the better ways to do this since they go fast and can actually travel some distance while still entangled. This is an intrinsically light-speed limited operation because it requires actual particles to be transmitted, and then of course the resulting entanglement can not be used for "instantaneous" communication either, so quantum teleportation has nothing whatsoever to do with faster communication. It's about securing it, not speeding it up. I would guess that the researchers themselves do not particularly love this summary of their work, but I'd also guess that they've thrown themselves against the brick wall of obstinate misunderstanding about everything "quantum" enough times that they may well have given up trying to get University PR to write about it accurately. There must be some training camp somewhere that they send all the aspiring science communicators to where they say the word "quantum" over and over and if the aspiring writers do not wiggle their fingers ominously and go "wooooo wooooo" in a scary Halloween voice in response every single time they hear it they get their hands thwacked by a ruler.
farceSpherule 2y ago
"...already carrying Internet traffic..." The cables in the study were not carrying any Internet traffic.
stevebmark 2y ago
You can’t send information through entangled particles. So what is the use of this?
- henry2023 2y ago
  The point of research is not if it's or isn't useful for practical purposes.
- ko27 2y ago
  Many potential use cases. Quantum key distribution, quantum imaging, quantum sensing etc.
- bookofjoe 2y ago
  Not yet. But not necessarily never...
  - stevebmark 2y ago
    The hell?
Havoc 2y ago
This entire paragraph is just breaking my mind. Need to find an quantum entanglement for dummies book or something >“By performing a destructive measurement on two photons — one carrying a quantum state and one entangled with another photon — the quantum state is transferred onto the remaining photon, which can be very far away,” said Jordan Thomas, a Ph.D. candidate in Kumar’s laboratory and the paper’s first author. “The photon itself does not have to be sent over long distances, but its state still ends up encoded onto the distant photon. Teleportation allows the exchange of information over great distances without requiring the information itself to travel that distance.”
- dietr1ch 2y ago
  https://en.wikipedia.org/wiki/Quantum_teleportation https://en.wikipedia.org/wiki/Quantum_teleportation > (...) quantum teleportation only transfers quantum information. The sender does not have to know the particular quantum state being transferred nor the location of the recipient, but to complete the quantum teleportation, classical information needs to be sent from sender to receiver. Because classical information needs to be sent, quantum teleportation cannot occur faster than the speed of light. From here it's mind blowing until the part where classical information needs to be sent. Then it only seems useful as a way to transfer quantum state safely and undetected. It's really cool that the classical information can be broadcasted, so you can keep the recipient's location secret. Maybe quantum cryptographic keys, if that's a thing, can be sent this way, or a channel that just teleports quantum data without a chance of of being overheard can be setup.
deleted 2y ago
[deleted]
brcmthrowaway 2y ago
Could this result in an ansible?
- fsh 2y ago
  No [1]. [1] https://en.m.wikipedia.org/wiki/No-communication_theorem https://en.m.wikipedia.org/wiki/No-communication_theorem
mmmBacon 2y ago
The presence of a 1550nm 400Gb/s signal is really just a distraction here and doesn’t add to the experiment in a meaningful way. I don’t think anyone is surprised that you can separate channels by wavelength, even if those channels are quantum. So this really comes down to observing teleportation given the high loss of the fiber at 1310nm at 30km. From that point of view the experiment is pretty solid but I’m not sure it’s worthy of a press release.
- magicalhippo 2y ago
  The lasers generating the signal are not perfect and generate a Gaussian-like profile of wavelengths, albeit narrow. In this experiment[1] they sent single photons alongside the classical data: Alice’s qubit is then encoded onto the horizontal (H) and vertical (V ) components of the heralded photon’s polarization |ψ〉A = α|H〉 + β|V 〉using polarization waveplates. This photon is then multiplexed using an O-band/C-band WDM to co-propagate with the 400-Gbps C-band classical signal over 15.2 km of spooled optical fiber (SMF-28(R) ULL) to Charlie. To prevent the detection of C-band photons due to insufficient filter isolation, we cascade two cascaded O-band/C-band WDMs before the FBGs and a 1290-nm DWDM to achieve >190 dB rejection of C-band light. WDM = wavelength division multiplexer, FBG = fiber Bragg grating[2]. If it was just a distraction, why did they bother adding 190+ dB of filter rejection? [1]: https://opg.optica.org/optica/fulltext.cfm?uri=optica-11-12-1700&id=565936 https://opg.optica.org/optica/fulltext.cfm?uri=optica-11-12-... [2]: https://en.wikipedia.org/wiki/Fiber_Bragg_grating https://en.wikipedia.org/wiki/Fiber_Bragg_grating
  - mmmBacon 2y ago
    The lasers are not Gaussian but Lorenztian. This is a detail that’s not terribly important. The lasers generate frequencies in C-band at ~194THz. The O-band photon source is ~229THz. Classically these fields do not interact. For passive beam splitting, there is also no quantum interference. The photo detectors are broadly sensitive to both frequency bands. So if the C-band light hits the photodiode you won’t be able to count photons. The filters are there to reduce the background “noise” of the C-band light hitting the photodiode that’s being used for photon counting. The use of filters for this purpose is very common and really not that interesting.

35 points by m-hodges 2y ago

The use of "Internet" in the title and article is deceptive. They did not send data over the Internet, they sent conventional optical data over a 30 mile spool of fiber and quantum entangled photons on an unused wavelength over the same cable in a laboratory setting.

ko27 2y ago
It's not deceptive. The whole point of the study was to figure out a way to transfer quantum information through active Internet cables, and not empty optical cables.
- fsh 2y ago
  I find the wording highly deceptive. The main feature making the internet globally scalable is not that it goes through fibers, but that it uses package routing. Nobody knows how to do this with qubits, so quantum communication doesn't scale at all. Instead, the community started doing these publicity stunts with very limited applicability.
  - swores 2y ago
    Their title is specific in saying "internet cables", not the internet. It seems fair to me that this is one step on the journey, that figuring out going through cables comes before figuring out routing between cables. It's a press release for a specific research paper, not a product release marketed to consumers. (Though it's possible the researchers themselves agree with you & iandanforth more than with me & ko27, as the title of the actual research paper itself doesn't use this wording; it's "Quantum teleportation coexisting with classical communications in optical fiber".)

inkcapmushroom 2y ago

Is anyone able to explain to me how this demonstrates "information without direct transmission" when a direct 30km fiber line is needed to transmit the data, and how you can call it teleportation when it's "limited by the speed of light"? Not doubting they did something special but I couldn't tell from the article what exactly it was that they did which is unique from standard fiber transmission (other than they received a single photon using an atypical frequency).

ko27 2y ago
This is basic QM "spooky action at a distance" stuff. Quantum information is teleported instantaneously, however to make use of that information, you actually need to transfer classical information over regular channels. That doesn't mean it's not useful, see for example the way QKD works: https://en.wikipedia.org/wiki/Quantum_key_distribution https://en.wikipedia.org/wiki/Quantum_key_distribution
eppp 2y ago
I know almost nothing about this but lay understand is this: the state of a photon can possibly be encoded with a vast amount of information, instead of transmitting that information encoded into light, they transmitted the state of entangled photons and thusly recreated the information on the third photon.
jerf 2y ago
Being generous, they say that "direct transmission" is not necessary because they are not "directly" transmitting a "1" or a "0", but instead an entanglement. I agree that, as is fairly usual for this field, this is poorly phrased, probably poorly understood by the writer, and prone to misinterpretation. There absolutely certainly is a "direct transmission" of some photons to achieve the effect, irreducibly so. You can't move entanglement around without some sort of carrier, photons in this case (as they are the most convenient for this task for much the same reasons they're quite convenient for conventional transmissions as well). Quantum teleportation is not related to speed. Quantum teleportation is when you entangle two particles, A and B, and then you take the entanglement on B and send the entanglement itself to some distant particle C. A and C are then entangled in exactly the same way that A and B were (this is the "teleportation"), and B no longer is. This is an intrinsically destructive operation on the original A/B entanglement. The requirement to be "quantum teleportation" is merely than the entanglement is transferred, regardless of speed; if you could send an entangled particle via the slowest shipping Fedex has and transfer the entanglement days later, that would still be quantum teleportation. However, it's all very delicate and that's not practical or possible, so photons are one of the better ways to do this since they go fast and can actually travel some distance while still entangled. This is an intrinsically light-speed limited operation because it requires actual particles to be transmitted, and then of course the resulting entanglement can not be used for "instantaneous" communication either, so quantum teleportation has nothing whatsoever to do with faster communication. It's about securing it, not speeding it up. I would guess that the researchers themselves do not particularly love this summary of their work, but I'd also guess that they've thrown themselves against the brick wall of obstinate misunderstanding about everything "quantum" enough times that they may well have given up trying to get University PR to write about it accurately. There must be some training camp somewhere that they send all the aspiring science communicators to where they say the word "quantum" over and over and if the aspiring writers do not wiggle their fingers ominously and go "wooooo wooooo" in a scary Halloween voice in response every single time they hear it they get their hands thwacked by a ruler.

farceSpherule 2y ago

"...already carrying Internet traffic..." The cables in the study were not carrying any Internet traffic.

stevebmark 2y ago

You can’t send information through entangled particles. So what is the use of this?

henry2023 2y ago
The point of research is not if it's or isn't useful for practical purposes.
ko27 2y ago
Many potential use cases. Quantum key distribution, quantum imaging, quantum sensing etc.
bookofjoe 2y ago
Not yet. But not necessarily never...
- stevebmark 2y ago
  The hell?

Havoc 2y ago

This entire paragraph is just breaking my mind. Need to find an quantum entanglement for dummies book or something >“By performing a destructive measurement on two photons — one carrying a quantum state and one entangled with another photon — the quantum state is transferred onto the remaining photon, which can be very far away,” said Jordan Thomas, a Ph.D. candidate in Kumar’s laboratory and the paper’s first author. “The photon itself does not have to be sent over long distances, but its state still ends up encoded onto the distant photon. Teleportation allows the exchange of information over great distances without requiring the information itself to travel that distance.”

dietr1ch 2y ago
https://en.wikipedia.org/wiki/Quantum_teleportation https://en.wikipedia.org/wiki/Quantum_teleportation > (...) quantum teleportation only transfers quantum information. The sender does not have to know the particular quantum state being transferred nor the location of the recipient, but to complete the quantum teleportation, classical information needs to be sent from sender to receiver. Because classical information needs to be sent, quantum teleportation cannot occur faster than the speed of light. From here it's mind blowing until the part where classical information needs to be sent. Then it only seems useful as a way to transfer quantum state safely and undetected. It's really cool that the classical information can be broadcasted, so you can keep the recipient's location secret. Maybe quantum cryptographic keys, if that's a thing, can be sent this way, or a channel that just teleports quantum data without a chance of of being overheard can be setup.

deleted 2y ago

[deleted]

brcmthrowaway 2y ago

Could this result in an ansible?

fsh 2y ago
No [1]. [1] https://en.m.wikipedia.org/wiki/No-communication_theorem https://en.m.wikipedia.org/wiki/No-communication_theorem

mmmBacon 2y ago

The presence of a 1550nm 400Gb/s signal is really just a distraction here and doesn’t add to the experiment in a meaningful way. I don’t think anyone is surprised that you can separate channels by wavelength, even if those channels are quantum. So this really comes down to observing teleportation given the high loss of the fiber at 1310nm at 30km. From that point of view the experiment is pretty solid but I’m not sure it’s worthy of a press release.

magicalhippo 2y ago
The lasers generating the signal are not perfect and generate a Gaussian-like profile of wavelengths, albeit narrow. In this experiment[1] they sent single photons alongside the classical data: Alice’s qubit is then encoded onto the horizontal (H) and vertical (V ) components of the heralded photon’s polarization |ψ〉A = α|H〉 + β|V 〉using polarization waveplates. This photon is then multiplexed using an O-band/C-band WDM to co-propagate with the 400-Gbps C-band classical signal over 15.2 km of spooled optical fiber (SMF-28(R) ULL) to Charlie. To prevent the detection of C-band photons due to insufficient filter isolation, we cascade two cascaded O-band/C-band WDMs before the FBGs and a 1290-nm DWDM to achieve >190 dB rejection of C-band light. WDM = wavelength division multiplexer, FBG = fiber Bragg grating[2]. If it was just a distraction, why did they bother adding 190+ dB of filter rejection? [1]: https://opg.optica.org/optica/fulltext.cfm?uri=optica-11-12-1700&id=565936 https://opg.optica.org/optica/fulltext.cfm?uri=optica-11-12-... [2]: https://en.wikipedia.org/wiki/Fiber_Bragg_grating https://en.wikipedia.org/wiki/Fiber_Bragg_grating
- mmmBacon 2y ago
  The lasers are not Gaussian but Lorenztian. This is a detail that’s not terribly important. The lasers generate frequencies in C-band at ~194THz. The O-band photon source is ~229THz. Classically these fields do not interact. For passive beam splitting, there is also no quantum interference. The photo detectors are broadly sensitive to both frequency bands. So if the C-band light hits the photodiode you won’t be able to count photons. The filters are there to reduce the background “noise” of the C-band light hitting the photodiode that’s being used for photon counting. The use of filters for this purpose is very common and really not that interesting.