Search found 17 matches

by Umberto Borla
21 Oct 2020, 12:45
Forum: Implementations
Topic: Implementing non on-site symmetries
Replies: 3
Views: 1336

Re: Implementing non on-site symmetries

Hi Johannes, thanks for your reply! Don't worry, from what I could understand I was expecting it to be a really challenging task. Just to provide some context, the original model is a gauge theory with fermionic matter. The mapping eliminates all gauge redundancy, so that the mapped model has a smal...
by Umberto Borla
15 Oct 2020, 14:14
Forum: Implementations
Topic: Implementing non on-site symmetries
Replies: 3
Views: 1336

Implementing non on-site symmetries

Hello, I am planning some large scale iDMRG simulations of a 2D spin model on the cylinder. The model has a global U(1) symmetry which could be exploited, corresponding to on-site particle number conservation in an analogous fermionic formulation of the model. In the spin language, however, the numb...
by Umberto Borla
23 Sep 2019, 15:03
Forum: HowTos and FAQ for TeNPy
Topic: how to write a three-site interaction?
Replies: 4
Views: 28887

Re: how to write a three-site interaction?

@QuichengTang: I'm glad to hear that this was useful.

@Johannes: Thanks for pointing it out, I forgot about it. I fixed it ;)
by Umberto Borla
10 Sep 2019, 17:17
Forum: HowTos and FAQ for TeNPy
Topic: how to write a three-site interaction?
Replies: 4
Views: 28887

Re: how to write a three-site interaction?

Hi! Using the multi-coupling model, you can use the function add_multi_coupling in the following way: self.add_multi_coupling(lambda_, 0, "Sigmax", [(0, "Sigmaz", 1), (0, "Sigmaz", 2)]) self.add_multi_coupling(lambda_, 0, "Sigmaz", [(0, "Sigmaz", 1),...
by Umberto Borla
05 Jul 2019, 16:14
Forum: HowTos and FAQ for TeNPy
Topic: Finite Chain with different unit cell at the beginning
Replies: 4
Views: 2679

Re: Finite Chain with different unit cell at the beginning

Thanks a lot for the quick reply! I imagined that changing the lattice would be enough, but I was not sure how to do. I'll see if I can manage to carry out the steps that you suggested. :)
by Umberto Borla
04 Jul 2019, 14:56
Forum: HowTos and FAQ for TeNPy
Topic: Finite Chain with different unit cell at the beginning
Replies: 4
Views: 2679

Finite Chain with different unit cell at the beginning

I am struggling with the following issue: I have a 1D lattice (chain) that consists of a repeated unit cell formed by two different sites (a spin-half site and a fermionic site). If I realize an open chain by repeating the unit cell L times, the first site will always be a spin site and the last one...
by Umberto Borla
13 Mar 2019, 10:52
Forum: HowTos and FAQ for TeNPy
Topic: Finite DMRG not working after update to new version
Replies: 4
Views: 2195

Re: Finite DMRG not working after update to new version

Thanks for the quick fix, it is working as expected now. :)
by Umberto Borla
12 Mar 2019, 17:34
Forum: HowTos and FAQ for TeNPy
Topic: Finite DMRG not working after update to new version
Replies: 4
Views: 2195

Re: Finite DMRG not working after update to new version

Hi! Thanks for the quick reply!
No, I find such error consistently every time I use finite DMRG. Even the example file xxz_groundstate, after a clean reinstall, does not run. Does it run without errors in the version that you have?
by Umberto Borla
12 Mar 2019, 17:02
Forum: HowTos and FAQ for TeNPy
Topic: Finite DMRG not working after update to new version
Replies: 4
Views: 2195

Finite DMRG not working after update to new version

Hi! After some months I finally decided to update to the newest version of TeNpy, and I found that my code does not work whenever it involves finite DMRG. The error that I get is: KeyError: "Label not found: '(vR.p1)', current labels: ['(vL.p0)', '(p1.vR)']" So it seems that something goes...
by Umberto Borla
12 Feb 2019, 11:09
Forum: HowTos and FAQ for TeNPy
Topic: Scaling of entanglement entropy for iDMRG
Replies: 7
Views: 3487

Re: Scaling of entanglement entropy for iDMRG

Hi! I am also looking into the scaling of S with \log \xi to extract the central charge and from what I read the relation you originally posted S \approx \frac{c}{6}\log \xi should be the correct one even for iDMRG. Apart from Calabrese and Cardy's original paper, here is a reference where they do i...
by Umberto Borla
15 Nov 2018, 10:03
Forum: Implementations
Topic: Multi-Site Expectation Value
Replies: 6
Views: 4392

Re: Multi-Site Expectation Value

Hi! This is the function modified according to your useful suggestions: def _term_to_jw(self, term, op_string = "JW"): """Given a term that is a tensor product of several operators acting on possibly non-neighboring sites [i_min, ... i_n, ... , i_max], this puts Jordan-Wigne...
by Umberto Borla
13 Nov 2018, 10:18
Forum: Implementations
Topic: Multi-Site Expectation Value
Replies: 6
Views: 4392

Re: Multi-Site Expectation Value

I implemented this function that takes a term containing operators acting on non-neighbouring sites and returns a list of operators, obtained by filling the intermediate sites with "Id" or "JW" where appropriate. The output can be used by the method expectation_value_multi_sites ...
by Umberto Borla
15 Oct 2018, 16:30
Forum: Implementations
Topic: Multi-Site Expectation Value
Replies: 6
Views: 4392

Multi-Site Expectation Value

I am developing the method that, given a MPS in canonical form, calculates the expectation value of multi-site operators that are tensor product of one-site operators. This is what I implemented so far: it works but does not handle operator strings (like the Jordan-Wigner string that is needed in th...
by Umberto Borla
15 Oct 2018, 10:30
Forum: Implementations
Topic: MultiCouplingModel and Toric Code as example
Replies: 7
Views: 5016

Re: MultiCouplingModel and Toric Code as example

I did some tests myself and i reached the same conclusion, that the MPO matrices give the correct Hamiltonian once multiplied together (I also tried explicitly for Ly = 3). I used the MPO matrices of TeNpy's toric-code model to create another toric-code model using the grid_outer method. For Lx=1, L...
by Umberto Borla
27 Aug 2018, 14:08
Forum: Implementations
Topic: MultiCouplingModel and Toric Code as example
Replies: 7
Views: 5016

Re: MultiCouplingModel and Toric Code as example

Oh I just saw your previous reply. Indeed, for L_y = 2 we get the same answers. The problem seems to be when L_y is odd.
by Umberto Borla
27 Aug 2018, 14:06
Forum: Implementations
Topic: MultiCouplingModel and Toric Code as example
Replies: 7
Views: 5016

Re: MultiCouplingModel and Toric Code as example

I tested your code a bit more and compared to mine, setting L_x = 1 in both cases (as we agree, it should not matter). What I found out is that the results coincide exactly with mine whenever L_y is even, and fails otherwise (e.g. the energy depends on L_x , the bond dimension is always saturated, e...
by Umberto Borla
27 Aug 2018, 10:29
Forum: Implementations
Topic: MultiCouplingModel and Toric Code as example
Replies: 7
Views: 5016

Re: MultiCouplingModel and Toric Code as example

Hi [mention]Johannes[/mention] . I am looking at how the multi-coupling model works. However I have a quick question specific to the toric code example. What is L_x, when the boundary conditions are set to "infinite" (infinite cylinder)? I thought it would be just a repetition of the unit ...