Entanglement of mixed hilbert space: How trace odd/even sites

ITensor Julia Questions
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1

Hi,

Let’s say I perform a DMRG calculation to a system with a mixed Hilbert space (as in the example of the documentation). How could I trace one species (for example the spin 1/2 sites in the example), and then calculate the von Neumann entropy? I know it is straightforward to calculate the entropy of a simple bipartition, but I wonder if I missing an obvious way to trace one type of quantum number instead.

Thanks!

2

Unfortunately that’s not an easy quantity to obtain from an MPS in a direct way. It is something that has been studied with tensor networks before, such as in this paper:

Glancing at the above paper, I think they settle for just obtaining two of the leading eigenvalues of the reduced density matrix rather than the whole spectrum that would be needed to compute the entropy.

3

Thanks! That’s what I suspected.