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arXiv · 1910.05970

Explicit properties of the simplest inhomogeneous Matrix-Product-State including the Riemann metric of the MPS manifold

Cecile Monthus
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Abstract

We consider the simplest inhomogeneous Matrix-Product-State for an open chain of N quantum spins that involves only two angles per site and two angles per bond with the following direct physical meanings. The two angles associated to the site $k$ are the two Bloch angles that parametrize the two orthonormal eigenvectors of the reduced density matrix $ρ_k$ of the spin $k$ alone. The two angles associated to the bond $(k,k+1)$ parametrize the entanglement properties of the Schmidt decomposition across the bond $(k,k+1)$. Explicit results are given for the reduced density matrix $ρ_{k,k+1}$ of two consecutive sites that is needed to evaluate the energy of two-body Hamiltonians, and for the reduced density matrix $ρ_{k,k+r}$ of two sites at distance $r$ that is needed to evaluate the spin-spin correlations at distance $r$. The global structure of the MPS manifold as parametrized by these $(4N-2)$ angles is then characterized by its explicit Riemann metric. Finally, the generalizations to any tree-like structure without loops and to the chain with periodic boundary conditions are discussed.

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Cecile Monthus. 2020-02-21. Explicit properties of the simplest inhomogeneous Matrix-Product-State including the Riemann metric of the MPS manifold. https://doi.org/10.1088/1742-5468%2Fab6b1b

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