Southwest Quantum Information and Technology

Feedback-based quantum algorithms

Presenting Author: Alicia Magann, Sandia National Laboratories
Contributing Author(s): Kenneth M. Rudinger, Matthew D. Grace, James B. Larsen, Andrew D. Baczewski, Mohan Sarovar

Variational quantum algorithms (VQAs) are a significant focus of the quantum computing community. These algorithms operate by wrapping a classical optimization loop around a parameterized quantum circuit, and iteratively searching for the parameter configuration that produces the best solution to the problem under consideration. A critical challenge in VQAs is the difficulty of this classical optimization problem, which can become intractable as the number of quantum circuit parameters increases. I will introduce feedback-based quantum algorithms (FQAs) as an alternative paradigm that is optimization-free and applicable to a broad range of applications. Within this paradigm, quantum circuit parameter values are assigned in a layer-wise manner using a deterministic, measurement-based feedback law derived from quantum Lyapunov control principles. The use of feedback in this manner guarantees a monotonic improvement in solution quality with respect to the depth of the quantum circuit. I will overview quantum Lyapunov control theory as a motivation for this framework and go on to discuss concrete formulations of FQAs for applications including quantum simulation and combinatorial optimization. I will conclude by presenting results from a hardware implementation and numerical investigations of convergence, scalability, and robustness. Sandia National Labs is managed and operated by NTESS under DOE NNSA contract DENA0003525. SAND2022-10773 A.

Read this article online: https://arxiv.org/abs/2103.08619, https://arxiv.org/abs/2108.05945

(Session 9b : Friday from 4:45 pm - 5:15 pm)