[idempotent_]

Interesting, a sort of quantum eruv https://en.wikipedia.org/wiki/Eruv

Does anyone have any additional context on the throughput numbers? It says 20k photons per second at 99% fidelity and 500k at 90%, but what is the actual bandwidth needed for reasonable usage / computation?

[golergka]

> In addition, it is also forbidden to transfer an object for a distance of 4 cubits

This gave me pause.

[ars]

In a public area you can not transport objects, the intention being that the Sabbath is a day of rest, and you should stay home or at least near your home and not do work.

Note: Jewish law very carefully defines "public area", and it would take several pages of text to fully explain it, so before objecting be aware you may be lacking background knowledge.

[dhosek]

I’m guessing it’s the cubits that gave pause more than the restriction. I first became aware of eruvim thanks to an article in the L.A. Times which talked about a new eruv being constructed in Venice. The article talked about the restriction on carrying and how the eruv allowed congregants to bring their keys¹ with them while attending synagogue.

⸻

1. Doubtless someone reading this is thinking, well, they could just get an electronic lock and use that to protect their homes but most Orthodox rabbis would prohibit this as there is the possibility of a spark being created by the electronic system² which would violate the prohibition on making a fire on the Sabbath.

2. This question comes up in Surely You’re Joking Mr Feynman, where Richard Feynman, asked about this by rabbinical students, told them that electricity was not fire and that a condenser across the switch would eliminate any potential spark, but they were unsatisfied with his answer.

[elahd]

Keys on shabbat is doable without an eruv¹²³. (It's not considered carrying if it's an integral part of your clothing.) Eruvs are more for strollers/carrying small kids, dessert/wine when invited for lunch, etc.

¹https://thekeybelt.com

²https://www.judaica-world.com/index.php/adjustable-shabbos-k...

³https://maps.app.goo.gl/ptpGhwLeckdUTjUd7

[dhosek]

Yeah, this is covered in the Eruv wikipedia article as well, but was not mentioned in the L.A. Times article (at least as far as I can remember—it’s been 15+ years since I read it).

[gradschoolfail]

Twice paused here

> bring their keys¹

Are these keys quantum??

Quantum-key bringing-about² is the main utility (afaik) of these underground quantum networks (pls don’t take this as an endorsement of the tech lol)

These networks have to work during Shabbat..

2 https://en.wikipedia.org/wiki/Quantum_key_distribution

[Log_out_]

Thus religous law gives birth to a new generation with a hacker mindset.

[tapotatonumber9]

Not 4 qubits?

[ars]

20k (10^4) photons/sec is a TINY amount.

An ordinary flashlight emits something like 10^18 photons per second. Even a star in the night sky sends around 10^8 to your eye.

That few photons is not going to have much bandwidth.

[asplake]

They’re measuring individual photons, right? I’m old enough to remember modems slower than that. No doubt they will get faster, but what if they were used only for (say) key exchange?

[krastanov]

"20k photons at 99% fidelity" usually means "we can detect each of these 20k photons separately with 1% error rate", which would be roughly 20kb/s. Low bandwidth, but it has little to do with how much light comes from a flash light or from the night sky, because they are using detectors that detect each photon (as opposed our eyes or typical network equipment which might need a large average number of photons per bit).

[jerf]

AIUI, this sort of system is likely to end up a lot like TLS negotiation and asymmetric crypto in general. Even if it never has very much bandwidth, the ability to share secrets on a channel that is not just declared secure by engineers, but declared secure by physics has some advantages. Asymmetric crypto is generally atrociously slow too, but incredible useful because we can use it to bootstrap symmetric crypto which is very fast.

Of course, if it does upgrade to the point that it can move gigabits per second, they'll use it for that. I don't know of a particular reason why this would be fundamentally impossible. I'm just saying that's not a necessary condition for the technology to be useful.