Use of a Quantum Computer and the Quick Medical Reference To Give an Approximate Diagnosis

The Quick Medical Reference (QMR) is a compendium of statistical knowledge connecting diseases to findings (symptoms). The information in QMR can be represented as a Bayesian network. The inference problem (or, in more medical language, giving a diagnosis) for the QMR is to, given some findings, find the probability of each disease. Currently known techniques for making inferences from the QMR Bayesian network use a conventional "classical" computer that performs sums of exponential size. In this paper, we show how to make approximate inferences from the QMR Bayesian network by running a quantum computer many times, each run consisting of only a polynomial number of steps. The inference improves with each run.