Experimental signatures of quantum annealing

Sergio Boixo, Tameem Albash, Federico M. Spedalieri +2 more

Sergio Boixo, Tameem Albash, Federico M. Spedalieri +2 more

Abstract : Quantum annealing is a general strategy for solving difficult optimization problems with the aid of quantum adiabatic evolution [1, 2]. Both analytical and numerical evidence suggests that under idealized, closed system conditions, quantum annealing can outperform classical thermalization-based algorithms such as simulated annealing [3, 4]. Do engineered quantum annealing devices effectively perform classical thermalization when coupled to a decohering thermal environment? To address this we establish, using superconducting flux qubits with programmable spin-spin couplings, an experimental signature which is consistent with quantum annealing, and at the same time inconsistent with classical thermalization, in spite of a decoherence timescale which is orders of magnitude shorter than the adiabatic evolution time. This suggests that programmable quantum devices, scalable with current superconducting technology, implement quantum annealing with a surprising robustness against noise and imperfections.

G. Aeppli, T. F. Rosenbaum

Wade DeGottardi, David Ferguson, С. А. Новиков +2 more

Sergio Boixo, Robert F. Lucas, Daniel A. Lidar +2 more

Abstract : Many computationally challenging problems can be reduced to Quadratic Unconstrained Binary Optimization (QUBO), which can be solved by a quantum evolution from a strong transverse field to a spin glass Hamiltonian (also known as quantum annealing or QA). We have examined open system QA, using theoretical and experimental techniques to deepen our understanding of open system QA by situating it in the context of related, well studied classical and quantum problems. We have explored and elucidated the significance of tunneling in QA with Path Integral Monte Carlo. We have also provided signatures of quantum behavior of QA against closely related simulated annealing implementations, analytically, numerically, and experimentally. We have carried out a comprehensive comparison of geometrically-local open-system QA and classical solvers for computationally hard problems such as MAX-2-SAT. We have exploited and further developed a graph-theoretical mapping between the Ising spin glass partition function and circuit model decision problems, discovered in a previous ARO Quantum Algorithms funded project. We have made significant progress on error correction techniques for QA, both theoretically and experimentally, and in demonstration of quantum speedup.

John P. S. Peterson, Roberto S. Sarthour, Alexandre M. Souza +3 more

Abstract A banged‐digital‐analog simulation of a quantum annealing protocol is performed in a two‐qubit nuclear magnetic resonance (NMR) quantum computer. The experimental simulation employs up to 235 Trotter steps, with more than 2000 gates (pulses), and a protocol success above 80% is obtained. Given the exquisite control of the NMR quantum computer, the simulation is also performed with different noise levels. Thus, the reliability of the quantum annealing process is is analyzed, and it is related to the level of entanglement produced during the protocol. Although the presence of entanglement is not a sufficient signature for a better‐than‐classical simulation, the level of entanglement achieved relates to the fidelity of the protocol.