Hybrid Computation for Consistent Histories

The consistent histories approach to quantum mechanics can be a valuable tool for studying many physical processes, ranging from the stochastic behavior of molecules to the quantum-to-classical transition. This approach resolves seeming paradoxes and allows us to apply classical logic to sequences of quantum events. Unfortunately, this tool has historically been limited to small systems or simple cases as the computational expense involved exponentially grows with both the system size and with the number of times considered on a classical computer, quickly becoming intractable. To remedy this difficulty, we present a hybrid quantum/classical algorithm suited for noisy intermediate-scale quantum computers that allows us to find and study consistent histories. We demonstrate the performance of this algorithm on the IBM and Rigetti quantum computers, and show a simulated demonstration of what will be possible on larger quantum computers. Finally, we discuss some potential future applications of this algorithm.