TeNPy Forum

Hello, I am running some quantum annealing simulations for the transverse field Ising model. At t=0 the Hamiltonian is just the field term and at t=T it's only the Ising terms with linear interpolation in-between. So far I have been just looping over time steps and initialized a new model with sligh...

Hey, is there a reference that I should cite if I use the 'folded' ordering? Seems like a well-known trick, but I wonder who 'did it first'.
Thanks!

Thank you very much for your detailed answer. Makes sense! I will try using different jobs instead of using multiprocessing.

Hey Johannes, ok thanks! This is what I wanted to know. So you're saying the the contraction with the approximated U is much more expensive than building it, whic makes sense! Because I apply the 'same circuit' to many different states all the time, I thought about calculating all the approximated U...

Hey, so I use the `ExpMPOEvolution` to time evolve some MPS. It takes a MPS and a model as an input. I want to time evolve many different MPS with the same Hamiltonian. Is there a way to only approximate the unitary time-evolution once and use it on the different states instead of recalculating it o...

So doing the above doesn't seem to work for me. I converged an MPS with variable bond dimension, and then fix chi_min=chi_max for a new run, using the MPS as initial state. However, the bond dimension won't change, because it immediately is converged without the bond dimension being changed (increas...

Hey Johannes, thanks for your reply. You are right. I am looking at an infinite system. Because even for iDMRG L>=2, I would like to construct a translationally invariant MPS for a single site. I calculate ground states over a range of parameters and would like to fix the form of the output MPS. So ...

Hey,
is there a way I tell tenpy to compute a MPS that consists only of square matrices?
Thanks!

Thank you very much for your reply. So checking the source codes it seems I'd have to use the 'make_measurement()' method. However, I want to measure something like this at each time step: for t in range(num_time_steps): env = MPSEnvironment(psi_0, evol.psi) out[t] = env.expectation_value(op, sites)...

Hello, I am calculating some expectation values for a range of time steps. I have some MPS psi_0 and the following evolution: evol_params = {'approximation': 'I', 'dt': 0.1, 'N_steps': 1} Let's say I want to calculate quantities at 100 time steps. What's the most efficient way of doing so? Should I ...

Dear Johannes, yes, I am using finite MPS. Thank you very much for opening up the issue on github. In my case it's actually not i+1, but actually i+2, because I am working on a ladder. I am actually not sure whether I understand why the example that you kindly provided works. So is it because you se...

Hi, I want to calculate the expectation value \langle \psi| S_i^z S_{i+1}^z |\phi \rangle . Because the two MPS are different, I create a tenpy.networks.mps.MPSEnvironment . What is the best way to compute the above correlation function? For tenpy.networks.mps.MPS there is tenpy.networks.mps.MPS.ter...

You are right. I only benchmarked up to ~256 where it wasn't so significant.
Thanks again, for the input!

Thank you very much for the answer. I implemented both and the results match. The difference in computation time was not so significant (for now), so I might stick to grouped sites because, as you said, they are kind of 'prettier' and easier to handle when extracting correlation functions etc. Again...

Hello, I have a unit cell with 2 FermionSite and I would like to implement a term like c^\dagger_{0, n+1}c^\dagger_{1, n+1}c_{1, n}c_{0, n} , where 0 and 1 are the sublattice indices and n runs over the unit cells. So something like a two-body hopping term (or can be thought of as a nearest neighbor...

Thank you very much for the quick update! I managed to reproduce the results with open boundary conditions for the 'folded' ladder, by reordering the expectations value. Next step is to try it out with the periodic boundary conditions. In the post you refer to you you write that you should set [tenp...

Dear Johannes,
Sorry, I had put this problem aside for a while. Anyway, thank you very much for your answer.

The 'folded' order is not yet implemented for the ladder system, right? Can I implement a custom order myself in the model that I built?

Best,
Niclas

Hello, I want to compare a finite system that has a surface with it's 'bulk-counterpart'. Using first DMRG calculations and then time-evolving methods I calculated the excitation spectrum. The size of the finite system was large enough, and it worked out well. However, now I want to compare it to th...

I recently switched to a computer running Apples new M1 chip. However, tenpy is not available for the M1 conda distribution. Should I just run it via Rosetta (Apple's Intel interface) or can we expect a M1 compatible package on conda any time soon?

Thank you very much for your reply and that new functionality! However, I didn't quite get how to construct the operator for two different sites. Reading the documentation it seems that I have to pass an array of strings to kron(), which will be translated into some local operators (e.g. 'Sz' for th...

Hi, is there an easy way to make custom operators and apply them to a MPS via 'mps.apply_local_op()'? Let's say I want to apply S^x_i + S^y_i+1 - const*Id. Is there some functionality that I can construct this operator, give a name to it, and then apply it? The 'const' is evaluated at runtime, so de...

Thank you very much for the additional information. This is super helpful! Best regards!

Dear Johannes, thank you very much for your help. For the moment I'm fine working with finite systems, as well. I mostly started with iDMRG because I followed the rough description given in Sec. IV in this work: https://arxiv.org/pdf/1804.06811.pdf it is explicitly mentioned that an iDMRG ground sta...

So after a couple of tests, the problem described above persists to occur for many combinations of states. At each time point t of the evolution I want to initialize an MPSEnvironment for all j for <psi_0 | psi_j> with |psi_j> being the time evolved state at time t with |psi_j> = U S_j |psi_0>, to t...

Sorry for my late reply, I really appreciate the help. Below you find the traceback, after I called MPSEnvironment(psi_0, testpsi) with psi_0 being an iDMRG ground state to which applied 'Sz' to some site with mps.apply_local_op, and testpsi the output of ExpMPOEvolution where psi_0.apply_local_op(s...