"QKD is already used by banks and governments to transmit keys over fibre optics."

I wonder what specific uses they mean. It's kind of hard to believe those are "serious" use-cases, going beyond demonstrations done for marketing reasons... Then again, as soon as you have a serious use-case, you don't tell anyone about it, so it's really hard to evaluate how much (if at all) this stuff is really used in practice.

Quantum key distribution is a real thing. It's a very specific set of constraints that would make it generally attractive, though, namely not relying on networks of trust to function, maybe? Key distribution as a dumb pipe.

I'm not asking if it's "a real thing". I'm asking if it's used anywhere, either commercially or -- in any case -- to encrypt actually sensitive data outside of tech demonstrations. I'm not aware of anything. China has a "qkd backbone" but if they're actually using it for anything is anyone's guess.

This seems like a really dumb thing to emphasize for marketing ends outside of actual competency. But what else is new!

I'm having trouble parsing your comment... What is a dumb thing? Who is emphasizing what?

Ah, understandable.

> what is a dumb thing?

Emphasizing quantum key control. In the situations where it's really relevant you don't need buy-in from investors, the value is evident.

Sayonara!

Intrusion detection for one:

https://patents.google.com/patent/US20070110247A1/en

https://journals.aps.org/prxquantum/abstract/10.1103/PRXQuan...

Those are a patent (with status "abandoned", whatever that means) and a scientific paper. Quite different from an instance where something is used in practice.

Do you know any instances of practical usage? People getting actual keys and using those to encrypt actual sensitive data?

Yes, hollow-core fibers also attenuate light.