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Comment by doctorfoo | Hacker News Reader

That makes it sound to me like the light was not stopped, merely the light's energy was stored. Which is quite a different thing?

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The important thing is that whatever information was encoded in the light was retained instantly. The only other way to do this is expensive photonics kit to convert light to electricity, then back to light. We're basically developing tools to achieve with light what we now do with electricity.

Also, light gets absorbed and retransmitted all the time in real life. The particular photons involved aren't really important in the typical notion of light.

Edit: to clarify, light in a medium is absorbed and reemitted, which is why light in atmosphere is slower than light in a vacuum. Between atoms it's just as fast, but there's latency in colliding, collapsing and reemitting.

There is no other way to do this, in this case they're maintaining information about the quantum properties of the beam (entanglement, etc.), which get destroyed if you convert it to electricity. When talking about quantum cryptography or, in general, quantum computing (as in "computations that are performed using the fundamental quantum interactions between particles"), the particular photons are indeed very important :)

Just to clarify (I'm pretty sure, but you seem knowledgeable), the quantum state is maintained when photons are absorbed/re-emitted by matter, right? Otherwise it seems like there would be a lot more vacuums involved. That was what I meant by 'the particular photons'; to my mind if you transmit your energy to an electron and are re-emitted you become a 'different' photon. It's a pretty silly point to argue about, though.

They're pretty sure it's the same light because (in other experiments with stopped light, not sure about this paper in particular) it maintained the same quantum information as the input light. Stopped light maintains superpositions etc.

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