Fast Quantum Subroutines for the Simplex Method

Abstract

What would Dantzig do with a quantum computer? It is unlikely we will ever find out the answer to this question. However, we can try to understand if the simplex method can be implemented on a quantum computer, and this might have piqued Dantzig’s interest. The paper “Fast Quantum Subroutines for the Simplex Method” gives a quantum implementation of an iteration of the simplex method, in which the basis inverse is never explicitly computed: the quantum computer takes as input the current basis and certifies optimality or outputs the next basis. Because computing the basis inverse is expensive, this can lead to an asymptotically faster algorithm in terms of the problem size: in the best case, the quantum algorithm can identify pivots in essentially linear time! This, however, comes at the cost of worse dependence on some numerical parameters: all these tradeoffs are discussed in the full article.