Re: Randomness from a Quantum source?



Unruh wrote:
Wolfgang Draxinger <wdraxinger@xxxxxxxxxxxxxxxx> writes:

David Eather wrote:

Please have a look at this thing:

http://www.idquantique.com/products/quantis.htm

It makes a claim of 4 or 16 Mbits per second of random data based a
quantum process. I don't dispute the method but is that kind of data
rate feasible / compatible with the concept of measuring one photon at a
time?

Of course. All you need is a very weak laser that produces that amount of
photons per second with a total random polarisation. At a wavelength of
640nm this amounts to a power of 0.7pW.

Getting a laser to produce "totally random polarizations is hard.

This laser is directed to a 50:50 beamsplitter, and at each branch a
avalance photodiode (those can detect single photons). One diode yields a
0-bit the other a 1-bit.

The question is whether or not the photodiode can recover on the 10s of
nanoseconds timescale. Also are you sure that the beamsplitter is really
50-50( biasing the 1s and 0s)? How are you sure? Are you sure that the photodiodes do not become
more/less sensitive after detecting a photon for a while (biasing the
consecutive 1 or 0), or that the dark noise changes after a detection?
Or that the diode produces 1/f noise? All physical systems have biases of some sort
or another. Now they are often predictable or correctable. But if you
are not careful, they bite you.


We have such a thingy at my university, and there's even a service for
students, that they can bring a mobile storage (HDD, USB flashdrive, etc.)
which is filled up with a perfect random bitstream.


Wolfgang


Bill,

If I may ask, how big a doubt would you have that this thing -

http://www.idquantique.com/products/quantis.htm

might not be producing true random data at the data rate suggested?
.



Relevant Pages

  • Re: Randomness from a Quantum source?
    ... It makes a claim of 4 or 16 Mbits per second of random data based a ... avalance photodiode. ... more/less sensitive after detecting a photon for a while (biasing the ... or that the dark noise changes after a detection? ...
    (sci.crypt)
  • Re: Randomness from a Quantum source?
    ... It makes a claim of 4 or 16 Mbits per second of random data based a ... avalance photodiode. ... more/less sensitive after detecting a photon for a while (biasing the ... I would worry about biases as I mentioned, ...
    (sci.crypt)
  • Re: Randomness from a Quantum source?
    ... It makes a claim of 4 or 16 Mbits per second of random data based a ... more/less sensitive after detecting a photon for a while (biasing the ... I would worry about biases as I mentioned, ... no. Lets say that the bias is 50.00001% vs a bias of 99.99999% the ...
    (sci.crypt)
  • Re: Randomness from a Quantum source?
    ... It makes a claim of 4 or 16 Mbits per second of random data based a ... avalance photodiode. ... more/less sensitive after detecting a photon for a while (biasing the ... I would worry about biases as I mentioned, ...
    (sci.crypt)
  • Re: Randomness from a Quantum source?
    ... It makes a claim of 4 or 16 Mbits per second of random data based a ... avalance photodiode. ... more/less sensitive after detecting a photon for a while (biasing the ... I would worry about biases as I mentioned, ...
    (sci.crypt)