| 1. |
- Mazurenko, V. V., et al.
(författare)
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First-principles modeling of magnetic excitations in Mn-12
- 2014
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 89:21, s. 214422-
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Tidskriftsartikel (refereegranskat)abstract
- We have developed a fully microscopic theory of magnetic properties of the prototype molecular magnet Mn-12. First, the intramolecular magnetic properties have been studied by means of first-principles density functional based methods, with local correlation effects being taken into account within the local density approximation plus U (LDA + U) approach. Using the magnetic force theorem, we have calculated the interatomic isotropic and anisotropic exchange interactions and full tensors of single-ion anisotropy for each Mn ion. Dzyaloshinskii-Moriya (DM) interaction parameters turned out to be unusually large, reflecting a low symmetry of magnetic pairs in molecules, in comparison with bulk crystals. Based on these results we predict a distortion of ferrimagnetic ordering due to DM interactions. Further, we use an exact diagonalization approach allowing one to work with as large a Hilbert space dimension as 108 without any particular symmetry (the case of the constructed magnetic model). Based on the computational results for the excitation spectrum, we propose a distinct interpretation of the experimental inelastic neutron scattering spectra.
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| 2. |
- Willsch, Dennis, et al.
(författare)
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Benchmarking Advantage and D-Wave 2000Q quantum annealers with exact cover problems
- 2022
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Ingår i: Quantum Information Processing. - : Springer Science and Business Media LLC. - 1570-0755 .- 1573-1332. ; 21:4
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Tidskriftsartikel (refereegranskat)abstract
- We benchmark the quantum processing units of the largest quantum annealers to date, the 5000 + qubit quantum annealer Advantage and its 2000+ qubit predecessor D-Wave 2000Q, using tail assignment and exact cover problems from aircraft scheduling scenarios. The benchmark set contains small, intermediate, and large problems with both sparsely connected and almost fully connected instances. We find that Advantage outperforms D-Wave 2000Q for almost all problems, with a notable increase in success rate and problem size. In particular, Advantage is also able to solve the largest problems with 120 logical qubits that D-Wave 2000Q cannot solve anymore. Furthermore, problems that can still be solved by D-Wave 2000Q are solved faster by Advantage. We find, however, that D-Wave 2000Q can achieve better success rates for sparsely connected problems that do not require the many new couplers present on Advantage, so improving the connectivity of a quantum annealer does not per se improve its performance.
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