6
What Do You Mean ‘‘Probably’’?

Any one who considers arithmetical methods of producing
random digits is, of course, in a state of sin.

John von Neumann [7]

Here’s the key to what we’re going to cover in this chapter: in any given situation, the sum of the probabilities of all the different possible things that could happen always add up to 1.

In this short chapter, I cover the basics of practical probability theory to get us started on quantum computing and its applications.

Topics covered in this chapter

6.1 Being discrete
6.2 More formally
6.3 Wrong again?
6.4 Probability and error detection
6.5 Randomness
6.6 Expectation
6.7 Markov and Chebyshev go to the casino
6.8 Summary