[TTN] Explore automatic structural optimisation #120
Description
Inspired from the ideas from this paper, I'd like to provide an automated structural optimisation algorithm to the TTN simulator.
- I believe this should be done regularly when applying a two-qubit gate if the bond dimension is deemed to be large enough that it's worth to try it.
- I believe this should restrict to keeping the tree balanced and just swapping qubits between leaves.
- I believe this swapping should be informed by the entropy (or Schmidt rank) between each pair of (qubit, leaf-node). This metric can be efficiently calculated from the TTN via qubit discarding.