Is there any way to make a 3-body LocalHam1D?

[ProThicc]

I am working on a hamiltonian with three-body terms. I was interested to create an MPO using LocalHam1D that would include H3 and three body terms passed into the argument. Is there an easier way to approach this already handled by QUIMB?

[jcmgray]

Hi @ProThicc, yes the new way to build operators is encapsulated in the quimb.operator module, there's an introduction here now: https://quimb.readthedocs.io/en/latest/operator/operator-basics.html. Here's a brief example:

import quimb.operator as qop

L = 10
H = qop.SparseOperatorBuilder()
for i in range(L - 2):
    H += 0.5, ("x", i), ("y", i + 1), ("z", i + 2)
H.show()
# SparseOperatorBuilder(nsites=10, nterms=8, locality=3)
# x y z . . . . . . .  +0.5
# . x y z . . . . . .  +0.5
# . . x y z . . . . .  +0.5
# . . . x y z . . . .  +0.5
# . . . . x y z . . .  +0.5
# . . . . . x y z . .  +0.5
# . . . . . . x y z .  +0.5
# . . . . . . . x y z  +0.5

Hmpo = H.build_mpo()
Hmpo.show()
# │2│3│4│4│4│4│4│3│2│
# ●─●─●─●─●─●─●─●─●─●
# │ │ │ │ │ │ │ │ │ │

[ProThicc]

Awesome! Thank you @jcmgray! I was looking for this exactly!

[ProThicc]

Is there a method in works for the three-site local hamiltonian builder for algorithms like PEPS?

[jcmgray]

It depends a bit on what algorithm you mean for PEPS tensor networks. You can call .build_local_ham() to build a dict of local terms, that some PEPS methods can use. But there is no PEPO builder for example yet.

[ProThicc]

Yes, I am especially looking for something similar to TEBD that considers the 3-site neighbour hamiltonians for simulation. I was able to create a LocalHam1D object with three site interaction by modifications, but I was wondering if there was any future plan to include TEBD to work with three-site interacting terms