Non-abelian symmetries in tensor networks: A quantum symmetry space approach

By Andreas Weichselbaum. 2012

244 citations recorded by the source corpus.

Abstract A general framework for non-abelian symmetries is presented for matrix-product and tensor-network states in the presence of well-defined orthonormal local as well as effective basis sets. The two crucial ingredients, the Clebsch–Gordan algebra for multiplet spaces as well as the Wigner–Eckart theorem for operators, are accounted for in a natural, well-organized, and computationally straightforward way. The unifying tensor-representation for quantum symmetry spaces, dubbed QSpace , is particularly suitable to deal with standard renormalization group algorithms such as the numerical renormalization group (NRG), the density matrix renormalization group (DMRG), or also more general tensor networks such as the multi-scale entanglement renormalization ansatz (MERA). In this paper, the focus is on the application of the non-abelian framework within the NRG. A detailed analysis is presented for a fully screened spin- 3/2 three-channel Anderson impurity model in the presence of conservation of total spin, particle–hole symmetry, and SU ( 3 ) channel symmetry. The same system is analyzed using several alternative symmetry scenarios based on combinations of U ( 1 ) charge , SU ( 2 ) spin , SU ( 2 ) charge , SU ( 3 ) channel , as well as the enveloping symplectic Sp ( 6 ) symmetry. These are compared in detail, including their respective dramatic gain in numerical efficiency. In the Appendix A Non-abelian symmetries 101 , Appendix B Numerical implementation , Appendix C Example , finally, an extensive introduction to non-abelian symmetries is given for practical applications, together with simple self-contained numerical procedures to obtain Clebsch–Gordan coefficients and irreducible operators sets. The resulting QSpace tensors can deal with any set of abelian symmetries together with arbitrary non-abelian symmetries with compact, i.e. finite-dimensional, semi-simple Lie algebras.

Subfields: Atomic and Molecular Physics, and Optics, Condensed Matter Physics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/993b2579b9dbb586f09829216768450d7b5fca1c

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Citations in the corpus

Matrix product states and projected entangled pair states: Concepts, symmetries, theorems (2020, background): “…tensor Ai can be written in terms of Clebsch-Gordan coefficients of irreducible representations of the group G and the variational degrees of freedom can be incorporated by adding multiplicities (McCulloch and Gulácsi, 2002; Sanz et al., 2009b; Singh et al., 2010; Weichselbaum, 2012; White, 1993).”
Efficient numerical simulations with Tensor Networks: Tensor Network Python (TeNPy) (2018, background): “[13,14,16,17] for the non-abelian case, which requires a change of the computational basis and is much more difficult to implement.”
The density matrix renormalization group for ab initio quantum chemistry (2014, background): “Non-multiplicity-free symmetries can also be exploited in DMRG, but require special considerations [170].”