best way to create equal amplitude superpositions in a specific quantum number sector

[vadimoganesyan]

hey Ryan, thanks.

I want to project your “X” (product) state to just one total Z sector – this will give an equal amplitude superposition of all states in that sector, which has entanglement but not much – only \chi\sim L/2 nonzero Schimdt values, which I assumed to mean it’s “easy”.

Amended:
I asked Claude for documentation for MaxEntagler just now and it backed off and elaborated on this approach which now makes sense – basically run DMRG to find a GS in that sector of a properly designed H, but I still need to check if it has any other hiccups. Let me know if you have a “standard” method for this.

Thanks again, Vadim
PS
I did find references to MaxEntangler on some forum last night but can’t find anymore), since I too suspected it hallucinated.
PPS

Project product state to fixed quantum number (QN conserving) MPS?

Hi! Is there any way of generating a quantum number conserving MPS by projecting a product state that is a superposition of different quantum numbers? The simplest example would be constructing a state with fixed S^z from a product state of s^x_j eigenstates e.g. \ket{+}_1\otimes \ket{+}_2\cdots \otimes\ket{+}_N. I could just construct the MPS by hand, but was wondering if there is another way. Thanks!