
Quantum Random Number Generator Created Using a Smartphone Camera - lelf
https://medium.com/the-physics-arxiv-blog/quantum-random-number-generator-created-using-a-smartphone-camera-602f88552b64
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HackinOut
The article is from May 9th. HN Discussion here:
[https://news.ycombinator.com/item?id=7728043](https://news.ycombinator.com/item?id=7728043)

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Xcelerate
The numbers may indeed be random, and they may be from a physical process, but
are they actually _quantum random_? As the article indicates, it is indeed
true that there is no method of determining whether a string of numbers that
looks random is actually random. You can tell if it's _not_ random through the
use of various statistical tests, but there may always be a test that hasn't
been invented yet that could reveal an underlying pattern.

However, distinguishing between quantum randomness and "other" randomness is
quite easy actually. You just ask: did the randomness come from the collapse
of a quantum state into an eigenstate of the observable being measured? (Now,
if it's already in an eigenstate, it will collapse to the same state, so you
have to prepare it in an eigenstate of an incompatible observable before
measuring a new observable.) The particular new eigenstate that it collapses
into will be -- according to the postulates of QM -- truly random.

So it seems to me that with this "QM random" source from the cell phone
sensor, the scientists should be analyzing the "purity" of the signals they
are using to generate their numbers. All kinds of factors could make the
results non-QM random: electrical noise, different kinds of light sources,
processing delays, etc. There's a lot of things to consider here.

(In fact, if you really wanted to be sure that it was QM random, you could
create an entanglement [which is a QM-only phenomenon] and then see if the
Bell correlations exist between the two entangled states.)

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Houshalter
Couldn't you just take a picture with the same camera and then hash it? The
probability of getting the exact same set of pixels is small and it's
certainly not predictable.

~~~
happyhappy
I wondered the same thing. Noise in the picture should also make it extremely
hard to predict. For cryptographic use one would only need 256 bits of entropy
to seed a CPRNG, and I can't see how this amount of entropy wouldn't be
present in a normal photo.

