Quantum Computing for Everyone

by Chris Bernhardt

We have only just started our study, so we are quite limited in what we can do. We can, however, generate random strings of binary digits. The experiment that generated random strings of Ns and Ss can be rewritten as a string of 0s and 1s. Consequently measuring spins of electrons first in the vertical and then in the horizontal direction gives a random string of 0s and 1s. This is probably the simplest thing that we can do with qubits, but surprisingly this is something that cannot be done with a classical computer. Classical computers are deterministic. They can compute strings that pass various tests for randomness, but these are pseudorandom, not random. They are computed by some deterministic function, and if you know the function and the initial seed input, you can calculate exactly the same string. There are no classical computer algorithms that generate truly random strings. Thus, already we can see that quantum computations have some advantages over classical ones. Before we start to describe other quantum computations we need to develop a precise mathematical model that describes what happens when we measure spin in various directions. This is started in the next chapter where we study linear algebra—the study of the algebra associated with vectors. * We will keep using the term spin because it is the standard terminology. But we are just determining the axis of the poles of a magnet.