Prospects for quantum enhancement with diabatic quantum annealing
It is argued for continued exploration in the QA framework on the basis that improved coherence times and control capabilities will enable the near-term exploration of several heuristic quantum optimization algorithms.
Abstract
We assess the prospects for algorithms within the general framework of\nquantum annealing (QA) to achieve a quantum speedup relative to classical state\nof the art methods in combinatorial optimization and related sampling tasks. We\nargue for continued exploration and interest in the QA framework on the basis\nthat improved coherence times and control capabilities will enable the\nnear-term exploration of several heuristic quantum optimization algorithms that\nhave been introduced in the literature. These continuous-time Hamiltonian\ncomputation algorithms rely on control protocols that are more advanced than\nthose in traditional ground-state QA, while still being considerably simpler\nthan those used in gate-model implementations. The inclusion of coherent\ndiabatic transitions to excited states results in a generalization called\ndiabatic quantum annealing (DQA), which we argue for as the most promising\nroute to quantum enhancement within this framework. Other promising variants of\ntraditional QA include reverse annealing and continuous-time quantum walks, as\nwell as analog analogues of parameterized quantum circuit ansatzes for machine\nlearning. Most of these algorithms have no known (or likely to be discovered)\nefficient classical simulations, and in many cases have promising (but limited)\nearly signs for the possibility of quantum speedups, making them worthy of\nfurther investigation with quantum hardware in the intermediate-scale regime.\nWe argue that all of these protocols can be explored in a state-of-the-art\nmanner by embracing the full range of novel out-of-equilibrium quantum dynamics\ngenerated by time-dependent effective transverse-field Ising Hamiltonians that\ncan be natively implemented by, e.g., inductively-coupled flux qubits, both\nexisting and projected at application scale.\n