
Entanglement-based secure quantum cryptography over 1,120 kilometres - bigpumpkin
https://www.nature.com/articles/s41586-020-2401-y
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haolez
Naive question: quantum entanglement can't break causality, right? We can't
use it for faster than light communication.

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api
You are correct, at least as far as current theory and technology is
concerned. There must be a conventional carrier signal and the actual latency
is the latency of that signal.

What entanglement may allow here is a perfect absolutely unbreakable one time
pad. It may allow encryption that is physically impossible to break over any
time span (without access to the devices on either end or a side channel
attack on those devices that is).

It may also allow this without asymmetric key exchange. Symmetric algorithms
like AES or ChaCha are still practically unbreakable with a quantum computer
as long as 256 bit keys are used, but quantum secure conventionally
compostable key agreement is still in the research stages.

