Bulletin of the American Physical Society
2018 Annual Meeting of the APS Four Corners Section
Volume 63, Number 16
Friday–Saturday, October 12–13, 2018; University of Utah, Salt Lake City, Utah
Session E02: CMP + Materials 4: Quantum Magnetism and Topological Effects |
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Chair: Boris Kiefer, New Mexico State University Room: JFB 102 |
Friday, October 12, 2018 1:30PM - 2:06PM |
E02.00001: Bose-Einstein Condensation in Quantum Magnets Invited Speaker: Dagmar Franziska Weickert Quantum magnets are insulating paramagnets exhibiting low-lying energy levels of integer spins that are separated by a few meV and tunable with the application of an external magnetic field. As demonstrated 60 years ago, integer spin states can be described in an elegant way as a gas of interacting bosons with hard-core repulsion. The boson concentration is controlled by the applied field, which acts as chemical potential. Uniaxial symmetry of the spin environment is a precondition for the gas of Bosons to condense in a phase coherent state (BEC), which is equivalent to field-induced XY-antiferromagnetism in spin language. In my talk, I will discuss two examples of quantum magnets with field-induced magnetic order. The first one is NiCl2-SC(NH2)2, also known as DTN, where Ni2+ single ion anisotropy D = 8.9K opens an energy gap between the Sz = 0 ground state and the Sz = ±1 first exited states. XY-antiferromagnetism is induced between Hc1 = 2T and Hc2 = 10.5T establishing DTN as a typical example for a single-Q BEC. The second compound, AgVOAsO4, is a quantum magnet based on V4+, S = 1/2 spins arranged in a complicated cross pattern of alternating spin chains with significant bond frustration. Measurements of the specific heat up to 28T reveal a double phase transition above 10T, where the spin gap closes. The double transition promotes AgVOAsO4 as a promising candidate for multi-Q BEC, with Q being the wave vector of the single-particle ground state in boson language. Multi-Q BECs have the potential to host topological spin textures such as magnetic vortex crystals, equivalent to skyrmions in metallic systems, but were never observed so far. |
Friday, October 12, 2018 2:06PM - 2:18PM |
E02.00002: String-Net Models: A Wide-class of Exactly Solvable Discrete Models for 2D Topological Phase of Quantum Matter Yong-Shi Wu In this talk, I will give an introduction to the string-net models as a wide-class of exactly solvable discrete models for 2D topological phases of quantum matter, as well as a summary of the conceptual progresses in formalism extension and the computational results for physical properties from my research group at University of Utah and collaborators. |
Friday, October 12, 2018 2:18PM - 2:30PM |
E02.00003: Spinful Aubry-André model in a magnetic field: Delocalization facilitated by a weak spin-orbit coupling Rajesh K Malla, Mikhail E Raikh Conventional Aubry André model is known to exhibit an insulator-metal transition upon increasing the hopping amplitude. Without external magnetic field, spin-orbit coupling leads to a simple renormalization of the hopping amplitude. However, when the degeneracy of the on-site energies is lifted by an external magnetic field, the interplay of Zeeman splitting and spin-orbit coupling has a strong effect on the localization length. We studied this interplay numerically. In the limit of large periods, our numerical results can be interpreted in the language of the phase-space trajectories. As a first step, we have derived analytically the energy dependence of the localization observed in numerical simulations of the original Aubry-André model with large periods. Our main finding1 is that a very weak spin-orbit coupling leads to delocalization of states with energies smaller than the Zeeman shift. The origin of the effect is the spin-orbit-induced opening of new transport channels. 1 Rajesh K. Malla and M. E. Raikh, Phys. Rev. B 97, 214209 (2018). |
Friday, October 12, 2018 2:30PM - 2:42PM |
E02.00004: Quantum Circuits for Braiding Gates in a Surface Code Brendan Pankovich, Yong-Shi Wu In this presentation we will present the framework of a new surface code, the string-net surface code, based on the the exactly-solvable Levin-Wen model for doubled topological phases. We present the circuits needed to encode quantum information in the many-body states of a two-dimensional network of qudits, as well as circuits to measure and manipulate the encoded states. This framework serves as both a quantum error-correcting code and a quantum simulator of Abelian doubled topological phases.
What distinguishes the string-net surface code from present surface code prototypes is the feature of topological symmetry in the Levin-Wen model. We use a discrete formulation of the topological symmetry to construct quantum circuits that realize these transformations. This enables encoded Clifford gates to be, in principle, achieved solely in terms of quantum circuits, contrasting with the current methods utilizing code deformation and lattice surgery. We describe the encoding of quantum information using gapped boundaries and demonstrate how to perform gates from the generalized Clifford group in a topologically protected manner, including the use of defect lines.
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Friday, October 12, 2018 2:42PM - 2:54PM |
E02.00005: Topological defects in the solid state Miles Clemens Yttrium Manganite (YMnO3) naturally forms interesting patterns in its domains which form one-dimensional topological defects in the solid. By use of symmetries of the crystal, it is possible to understand why these domain patterns form and predict similar patterns that might form in other materials. |
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