Encrypted communications and other technologies require billions of random bits per second, but generating them in software isn’t truly random. Chaotic laser signals can also produce randomness, but now Wen Li, of the Chinese Academy of Sciences in Suzhou, and her colleagues report in Physical Review Letters a simpler, all-electronic system that might someday become a “random bit chip.” It uses chaotic currents in a superlattice to generate billion random bits per second.
The superlattice used by the team was like a multilayered semiconductor sandwich that presented vertically traveling electrons with two sequential barriers. Such a structure leads to plateaus in the current-voltage curve. Fixing the voltage at one of these plateaus can produce a current that spikes at random intervals, roughly every nanoseconds. Last year Li and colleagues reported that the amplitude of this current might be suitable for rapid random bit generation.
Now Li and her Chinese colleagues along with collaborators from Bar-Ilan University in Israel have put this superlattice through its paces, using two different signal processing techniques to increase the “bumpiness” of the current signal between spikes. With a more rapidly varying signal, the team could generate a higher rate of random bits. The first technique involved taking multiple derivatives; the second involved combining several sections of the signal from different times. In each case, the team saved only the last four or five “least significant” bits of each point sampled from the amplitude to add to the random bit stream and then verified the randomness with statistical tests. They say either technique or a combination may be appropriate, depending on experimental requirements. – David Ehrenstein