An efficient algorithm for computing entanglement entropy in systems with a restricted Hilbert space or U(1) symmetry

Published: 30 June 2025| Version 1 | DOI: 10.17632/d8s5byx96r.1
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Description

We present an efficient algorithm for computing entanglement entropies in systems with a restricted Hilbert space or U(1) symmetry. For the case of a restricted Hilbert space, the algorithm is straightforward in that only a map table from physical states to indices of an intermediate matrix is needed. In systems with a U(1) symmetry, the reduced density matrix can be put into a block-diagonal form by properly grouping matrix elements according to the total charge in the subsystem, leading to a significant boost in the efficiency of entanglement entropy calculation.

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Condensed Matter Physics, Computational Physics, Entropy, Quantum Entanglement

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