Peering into the anneal process of a quantum annealer

Presenting Author: Hristo Djidjev, Los Alamos National Laboratory
Contributing Author(s): Elijah Pelofske, Georg Hahn

To solve an optimization problem using a commercial quantum annealer, one has to represent the problem of interest as an Ising or QUBO (quadratic unconstrained binary optimization) problem and submit its coefficients to the annealer, which then returns a user-specified number of low-energy solutions. It will be useful to know what happens in the quantum processor during the anneal process so that one could design better algorithms or suggest improvements to the hardware. However, existing quantum annealers are not able to directly extract such information from the processor. Hence, in this work we propose to use advanced features of the newest annealer generation, the D-Wave 2000Q (DW2KQ), to indirectly infer information about the anneal process evolution. Specifically, DW2KQ allows users to customize the anneal schedule, that is, the schedule with which the anneal fraction is changed from the start to the end of the anneal. Using this feature, we design a set of modified anneal schedules whose outputs can be used to generate information about the states of the system at equally spaced time points during a standard anneal of Q. With this process, called slicing, we obtain approximate distributions of lowest-energy anneal solutions as the anneal time evolves. We use our technique to obtain a variety of insights into DW2KQ such as when individual bits in an evolving solution flip during the anneal process and when they stabilize, and the freeze-out points for individual qubits.

Read this article online: https://arxiv.org/abs/1908.02691

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