Entangled Photons Maintained Under New York Streets | Hacker News Reader

Entangled Photons Maintained Under New York Streets

physics.aps.org

91 pointslc0_stein35 comments

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?

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

This gave me pause.

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.

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.

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

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).

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

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

Not 4 qubits?

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.

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?

"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).

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.

This is great but why can’t i get fiber internet in my bk apartment. Still struggling with spectrum coaxial pulling less than 5mbps today. No options on my block. Sheesh

Find a new apartment? Here's the FCC broadband map: https://broadbandmap.fcc.gov/home

Doesn't that map consider an entire region serviced if a single residence in that entire region can get the advertised speeds?

That is technically true but usually companies don't invest the kind of resources to support fiber just to service a handful of residences. Once the infrastructure is in place, you usually try to deploy it to as many homes as possible.

If further expansion is seen as unlikely to recoup costs then what's to say an entire neighborhood has service when fiber has only been run to a single apartment?

I've seen complaints amounting to this exact scenario for years.

My friend has the opposite problem. The ISP's map claims to offer fiber service on his whole block, and if you type in your address they'll even offer service at that specific address. The problem is his block is at least 80% multi-tenant dwellings, and they'll only do new installs if everyone in the building subscribes. They don't just want permission from the landlord to wire the whole building at once to save time if future tenants subscribe, they're just not gonna do it unless everyone pays. In my friend's case, they didn't even tell him this ahead of time, despite explicitly saying he was in an apartment on the form he filled out when he attempted to sign up. They just "helpfully" change it to a request for DSL service. This was explained to my friend by the technician that showed up with DSL hardware only capable of a faction of the speed he was currently getting on coax. Obviously, he refused service. Then he got to fight AT&T for a few months over bills for DSL services he never requested, and rental for hardware he never accepted.

that map is a great resource, thank you

Is this solution to every issue in the US? Like if something is shit then instead of fixing just run from the problem? I guess that’s why you are stuck choosing between republicans and democrats every 4 years lol.

The reason Republicans and Democrats win all the time is partly because the US generally doesn't have ranked choice voting when it comes to something like presidential elections [0]. People are afraid of voting for a third party because it is unlikely they would win, so they vote as if betting or hedging, choosing the least bad and yet still likely to win against the worse option. With ranked choice voting, voters could choose their preferred candidate first, and their backup second, and this would introduce some dynamism into the political system.

[0] https://en.wikipedia.org/wiki/Ranked-choice_voting_in_the_Un...

EDIT: Rated voting seems even better [1]

[1] https://en.wikipedia.org/wiki/Rated_voting

"Why doesn't _EVERYONE_ move where broadband is!"

Except, uhhhhhhhhhhh, they can't.

Silicon Valley moment from gp

How does one detect whether a pair is still entangled?

I don't know how they did it, but verifying Bells inequality would do it if you made many pairs

I'm under the impression you can't. You create an environment that is more likely to keep the sets of particles from interacting with anything else and then you create an entangled pair. To confirm the entanglement I believe would take several measurements of several pairs of particles and these measurements would result in a probability that they were still entangled, not a certainty.

I found this explanation:

https://www.quora.com/Is-it-possible-to-detect-if-a-particle...

In my opinion, it's not the entanglement that is interesting or confusing, it's the super positions of both particles before they are measured that is hard to explain... How can two particles be in super positions of two states but then when you measure them they are always complimentary? Either it was "spooky action at a distance" ie (particle A communicated it's measurement result to particle B) or there is "hidden variables" inside the super positions that determines the result of the measurements.

Easy-peasy. They will periodically see if the photons, when measured had already been measured by an eavesdropper. In quantum world measurement will affect the entangled system, so it’s impossible for someone to measure (read) the data in between without it being detected at both ends.

> so it’s impossible for someone to measure (read) the data in between without it being detected at both ends.

You give too little information for this to be understandable.

That's one of the fundamentals of quantum mechanics. How that works on the intuitive level, is still being debated. All the mathematics and the experimental results support that with an extremely high level confidence though.

Not sure if a HN comment is a right to go back to the fundamentals here either, but I'll try again: reading the quantum information means to "measure it". Measurement alters the state of the system. If someone then "measures" it (i.e. "reads", i.e "eavesdrops"), the communicating parties will find out.

Check correlation via interference. They'll give consistent results if entangled, and random results if they're not.

Perhaps by checking their Instagram status.

There's a TMNT reference lurking here somewhere :)

I knew those turtles were up to something!

Everything was fine with our entangled photon system until the power grid was shut off by d*ckless here

Damn, you got there before me!

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