# \#mpo **URL:** https://itensor.discourse.group/tag/mpo/11.md [Latest](https://itensor.discourse.group/latest.md) · [Categories](https://itensor.discourse.group/categories.md) · [Tags](https://itensor.discourse.group/tags.md) --- ## [Green's function via method:apply(Jordan-wigner..."Cdagup"|0\>)](https://itensor.discourse.group/t/greens-function-via-method-apply-jordan-wigner-cdagup-0/2628)
**Author:** [@Leon](https://itensor.discourse.group/u/Leon)\ **Replies:** 5\ **Last updated:** [July 20, 2026, 12:05pm UTC](https://itensor.discourse.group/t/greens-function-via-method-apply-jordan-wigner-cdagup-0/2628 "2026-07-20T12:05:20Z")
Hello there, I was planning to compute greater and lesser Green’s functions for an tight binding model I was intereseted in. After some try and error, I noticed my implementation was lagging the Jordan Wigner string ope… --- ## [Question About MPO Compression Algorithms in ITensor](https://itensor.discourse.group/t/question-about-mpo-compression-algorithms-in-itensor/2613)
**Author:** [@kevinh](https://itensor.discourse.group/u/kevinh)\ **Replies:** 1\ **Last updated:** [May 8, 2026, 9:38pm UTC](https://itensor.discourse.group/t/question-about-mpo-compression-algorithms-in-itensor/2613 "2026-05-08T21:38:01Z")
Dear ITensor team, I am currently studying MPO compression algorithms, in particular the arXiv paper by Parker, Cao, and Zaletel, Local Matrix Product Operators: Canonical Form, Compression, & Control Theory (arXiv:1909… --- ## [Time dependent correlation functions with TDVP](https://itensor.discourse.group/t/time-dependent-correlation-functions-with-tdvp/2588)
**Author:** [@zeqetolaj](https://itensor.discourse.group/u/zeqetolaj)\ **Replies:** 4\ **Last updated:** [March 6, 2026, 11:05pm UTC](https://itensor.discourse.group/t/time-dependent-correlation-functions-with-tdvp/2588 "2026-03-06T23:05:02Z")
Greetings everyone, I intend to calculate the time dependent correlation function with TDVP algorithm. I applied the 2-site TDVP. The result is a bit strange, since the correlation function is oscillating (negative and… --- ## [Fermionic hopping dressed with quantized Peierls phase and conservation of fermions](https://itensor.discourse.group/t/fermionic-hopping-dressed-with-quantized-peierls-phase-and-conservation-of-fermions/2574)
**Author:** [@FerdinandToelkes](https://itensor.discourse.group/u/FerdinandToelkes)\ **Replies:** 1\ **Last updated:** [February 23, 2026, 8:15am UTC](https://itensor.discourse.group/t/fermionic-hopping-dressed-with-quantized-peierls-phase-and-conservation-of-fermions/2574 "2026-02-23T08:15:51Z")
Hello again, I am working on the one dimensional extended Hubbard model for spinless fermions and a light matter coupling that is introduced via the quantized Peierls phase. I want to implement this for open and periodi… --- ## ["In-place" sparse MPS for boundaryMPS](https://itensor.discourse.group/t/in-place-sparse-mps-for-boundarymps/2585)
**Author:** [@nimaser](https://itensor.discourse.group/u/nimaser)\ **Replies:** 0\ **Last updated:** [February 17, 2026, 6:45pm UTC](https://itensor.discourse.group/t/in-place-sparse-mps-for-boundarymps/2585 "2026-02-17T18:45:00Z")
I want to do boundary MPS on a sparse PEPS tensor network using the ITensorMPS library, where each row of the PEPS is treated as an MPS (or MPO?). It seems like all of the MPS functions in the library expect a single ten… --- ## [MPS and MPO in Quantum Circult](https://itensor.discourse.group/t/mps-and-mpo-in-quantum-circult/2577)
**Author:** [@yedi](https://itensor.discourse.group/u/yedi)\ **Replies:** 1\ **Last updated:** [January 30, 2026, 8:43pm UTC](https://itensor.discourse.group/t/mps-and-mpo-in-quantum-circult/2577 "2026-01-30T20:43:19Z")
Dear porfessors, In my previous work, I have used DMRG in ITensor to study the properties of two-dimensional Fermi–Hubbard model. I am also aware that ITensor provides a module for quantum circuit simulation. This natu… --- ## [Purifying MPO into MPS](https://itensor.discourse.group/t/purifying-mpo-into-mps/2534)
**Author:** [@oskar-novak](https://itensor.discourse.group/u/oskar-novak)\ **Replies:** 3\ **Last updated:** [November 26, 2025, 4:14am UTC](https://itensor.discourse.group/t/purifying-mpo-into-mps/2534 "2025-11-26T04:14:39Z")
I’m trying to take an MPO representing a density operator and turn it into a doubled MPS via contracting Bell states to the unprimed indexes. However, when I try to split the newly contracted tensors into two using SVD … --- ## [Computing Renyi entropy of a sub-system in the middle of a 1D chain](https://itensor.discourse.group/t/computing-renyi-entropy-of-a-sub-system-in-the-middle-of-a-1d-chain/2523)
**Author:** [@tamoghnaRay](https://itensor.discourse.group/u/tamoghnaRay)\ **Replies:** 3\ **Last updated:** [November 7, 2025, 2:57pm UTC](https://itensor.discourse.group/t/computing-renyi-entropy-of-a-sub-system-in-the-middle-of-a-1d-chain/2523 "2025-11-07T14:57:27Z")
Hi, I have a spin- 1/2 XXZ chain of length L. I have a sub-system of length L\_S, in the middle of the chain. Say L = 10 and the system goes from site 4 to 7 (L\_S = 4). I want to compute S\_n = \\frac{1}{1-n}\\log\[\\text{Tr} … --- ## [Unexpected error with number-conserving MPO when result is zero](https://itensor.discourse.group/t/unexpected-error-with-number-conserving-mpo-when-result-is-zero/2521)
**Author:** [@phx](https://itensor.discourse.group/u/phx)\ **Replies:** 2\ **Last updated:** [November 1, 2025, 7:02pm UTC](https://itensor.discourse.group/t/unexpected-error-with-number-conserving-mpo-when-result-is-zero/2521 "2025-11-01T19:02:55Z")
The following code gives an error which I don’t understand. I set up two different states with number conservation active: using ITensors, ITensorMPS N = 3 s = siteinds("Electron", N; conserve\_nf=true) x = MPS(s, \["Emp… --- ## [Using the sum of exponentials to fit long-range interactions](https://itensor.discourse.group/t/using-the-sum-of-exponentials-to-fit-long-range-interactions/2483)
**Author:** [@Ang](https://itensor.discourse.group/u/Ang)\ **Replies:** 2\ **Last updated:** [September 6, 2025, 11:05am UTC](https://itensor.discourse.group/t/using-the-sum-of-exponentials-to-fit-long-range-interactions/2483 "2025-09-06T11:05:37Z")
This question comes from a GitHub discussion. According to the answer there, the OpSum function from the Julia version will automatically compress the MPO. Is that correct? The original question is as follows. Several … --- ## [Explicitly Limiting the Bond Dimension of MPO upon Construction](https://itensor.discourse.group/t/explicitly-limiting-the-bond-dimension-of-mpo-upon-construction/2469)
**Author:** [@BenRClark](https://itensor.discourse.group/u/BenRClark)\ **Replies:** 3\ **Last updated:** [August 28, 2025, 2:32pm UTC](https://itensor.discourse.group/t/explicitly-limiting-the-bond-dimension-of-mpo-upon-construction/2469 "2025-08-28T14:32:34Z")
Hello, I am wondering in general if we can limit the bond dimension of an MPO upon its construction. I am interested in this because my MPO currently takes up far too much memory to be used efficiently. I suspect the bo… --- ## [Modified TEBD with QR decomposition](https://itensor.discourse.group/t/modified-tebd-with-qr-decomposition/2468)
**Author:** [@Wang](https://itensor.discourse.group/u/Wang)\ **Replies:** 1\ **Last updated:** [August 18, 2025, 10:32pm UTC](https://itensor.discourse.group/t/modified-tebd-with-qr-decomposition/2468 "2025-08-18T22:32:18Z")
Hello everyone! This paper \[ Fast time evolution of matrix product states using the QR decomposition | Phys. Rev. B\] develops a modified TEBD or Trotter gates time-evolving method in which SVD is replaced by QR+LQ decom… --- ## [How to set the bond dimension of a MPO](https://itensor.discourse.group/t/how-to-set-the-bond-dimension-of-a-mpo/233)
**Author:** [@jisutich](https://itensor.discourse.group/u/jisutich)\ **Replies:** 8\ **Last updated:** [August 14, 2025, 5:08pm UTC](https://itensor.discourse.group/t/how-to-set-the-bond-dimension-of-a-mpo/233 "2025-08-14T17:08:13Z")
Hi I am doing some time evolution simulation with a MPO as my density operator (mixed state). I find that when the system size grows, the memory usage is a big problem. I think this may be solved by limiting my bond dim… --- ## [TDVP for a Mixed Site System](https://itensor.discourse.group/t/tdvp-for-a-mixed-site-system/2463)
**Author:** [@chemicalfiend](https://itensor.discourse.group/u/chemicalfiend)\ **Replies:** 3\ **Last updated:** [August 12, 2025, 3:32am UTC](https://itensor.discourse.group/t/tdvp-for-a-mixed-site-system/2463 "2025-08-12T03:32:46Z")
Hello! I have a question about running TDVP for a mixed-site system of bosons and fermions. I have a system with nearest-neighbor coupled fermionic sites each coupled locally to bosonic sites (Hamiltonian generated roug… --- ## [Writing the following Hamiltonian as MPOs for DMRG calculation](https://itensor.discourse.group/t/writing-the-following-hamiltonian-as-mpos-for-dmrg-calculation/2459)
**Author:** [@Brian-Khor](https://itensor.discourse.group/u/Brian-Khor)\ **Replies:** 1\ **Last updated:** [August 1, 2025, 6:41pm UTC](https://itensor.discourse.group/t/writing-the-following-hamiltonian-as-mpos-for-dmrg-calculation/2459 "2025-08-01T18:41:22Z")
Dear Admin, I’m trying to find the ground state for the following Hamiltonian via DMRG (for a spin-half chain of 2N sites): H = \\sum\_{k=1}^{N} c\_k (Z\_{2k-1} - Z\_{2k})^2 + \\frac{J}{2N} ( H\_{odd/Left} - H\_{even/Right} … --- ## [Reduced density matrix of an MPO](https://itensor.discourse.group/t/reduced-density-matrix-of-an-mpo/2441)
**Author:** [@gso](https://itensor.discourse.group/u/gso)\ **Replies:** 5\ **Last updated:** [July 16, 2025, 2:25pm UTC](https://itensor.discourse.group/t/reduced-density-matrix-of-an-mpo/2441 "2025-07-16T14:25:23Z")
Hello, I want to obtain the reduced density matrix of a subsystem given a total density matrix. Here is a minimal working example. N = 4 sites = siteinds("S=1/2", 2N; conserve\_qns=false) sites\_p = prime(sites) ψ = ra… --- ## [METTS for Majorana fermion](https://itensor.discourse.group/t/metts-for-majorana-fermion/2426)
**Author:** [@prange](https://itensor.discourse.group/u/prange)\ **Replies:** 2\ **Last updated:** [June 22, 2025, 11:13am UTC](https://itensor.discourse.group/t/metts-for-majorana-fermion/2426 "2025-06-22T11:13:53Z")
Hi, I am trying to implement the METTS ( Phys. Rev. Lett. 102, 190601 (2009); New J. Phys. 12 055026 (2010)) for interacting Kitaev chain (Grand canonical ensemble). But with a problem on the choice/implementation of c… --- ## [Outer function errors, Mutual Information](https://itensor.discourse.group/t/outer-function-errors-mutual-information/2422)
**Author:** [@PZuiuc](https://itensor.discourse.group/u/PZuiuc)\ **Replies:** 5\ **Last updated:** [June 13, 2025, 3:03pm UTC](https://itensor.discourse.group/t/outer-function-errors-mutual-information/2422 "2025-06-13T15:03:18Z")
In the following code, after obtaining the ground state psi of the Hamiltonian H using DMRG, I verify the normalization by checking inner(psi, psi) and trace(rho), where rho = outer(dag(psi), psi). I find that inner(psi,… --- ## [Real time evolution with H(t)](https://itensor.discourse.group/t/real-time-evolution-with-h-t/2413)
**Author:** [@yedi](https://itensor.discourse.group/u/yedi)\ **Replies:** 1\ **Last updated:** [June 11, 2025, 7:50am UTC](https://itensor.discourse.group/t/real-time-evolution-with-h-t/2413 "2025-06-11T07:50:45Z")
Dear professors, I have read this tutorial about MPS time evolution. However, my chain Hamiltonian is time-dependent, for exmaple H(t)=\\sum\_j \\cos (\\omega t)h\_{j,j+1}. Because the Hamiltonians at different times do n… --- ## [Automatic JWT handling in \`AutoMPO\` and \`op\` functions](https://itensor.discourse.group/t/automatic-jwt-handling-in-autompo-and-op-functions/2404)
**Author:** [@jackaraz](https://itensor.discourse.group/u/jackaraz)\ **Replies:** 5\ **Last updated:** [June 3, 2025, 9:59pm UTC](https://itensor.discourse.group/t/automatic-jwt-handling-in-autompo-and-op-functions/2404 "2025-06-03T21:59:48Z")
Hi all, I’m working on a fermionic model which I create the hamiltonian using AutoMPO and siteinds("Fermion", N; conserve\_qns=true). Formulation of the hamiltonian is not an issue but I want to compute some observables … --- ## [Qudits/Boson observable expectation problems](https://itensor.discourse.group/t/qudits-boson-observable-expectation-problems/2406)
**Author:** [@douzi](https://itensor.discourse.group/u/douzi)\ **Replies:** 1\ **Last updated:** [June 2, 2025, 5:16pm UTC](https://itensor.discourse.group/t/qudits-boson-observable-expectation-problems/2406 "2025-06-02T17:16:02Z")
Hello, I am using ITensor with Julia, and I have a question regarding measuring expectation on Bosons or Qudits. I have searched for many hours and chated with GPT but there are always issues, so I wanted to ask my quest… --- ## [Problem using TEBD algorithm to represent Gibbs states](https://itensor.discourse.group/t/problem-using-tebd-algorithm-to-represent-gibbs-states/2356)
**Author:** [@jorgesanseg](https://itensor.discourse.group/u/jorgesanseg)\ **Replies:** 3\ **Last updated:** [May 29, 2025, 9:45am UTC](https://itensor.discourse.group/t/problem-using-tebd-algorithm-to-represent-gibbs-states/2356 "2025-05-29T09:45:25Z")
Hi, I am trying to get thermal states \\rho\_\\beta = e^{-\\beta H} mean values of local observables for long-range interacting system. More concretely the Long Range Spin chain: H\_{\\text{LR, Ising}}= J \\sum\_{i \\neq j}^N… --- ## [Restart DMRG with stored MPS](https://itensor.discourse.group/t/restart-dmrg-with-stored-mps/2386)
**Author:** [@yedi](https://itensor.discourse.group/u/yedi)\ **Replies:** 2\ **Last updated:** [May 14, 2025, 11:20am UTC](https://itensor.discourse.group/t/restart-dmrg-with-stored-mps/2386 "2025-05-14T11:20:20Z")
Dear professors, Recently, I use Julia Itensor to calculate the two-dimensional Hubbard model. I define my sites and MPO. sites = siteinds("Electron", N ; conserve\_qns=true, conserve\_sz=false); H = MPO(os, sites); p… --- ## [The ProjMPO-ITensor product error message inside tdvp](https://itensor.discourse.group/t/the-projmpo-itensor-product-error-message-inside-tdvp/2368)
**Author:** [@Zhen\_H](https://itensor.discourse.group/u/Zhen_H)\ **Replies:** 5\ **Last updated:** [May 4, 2025, 6:34pm UTC](https://itensor.discourse.group/t/the-projmpo-itensor-product-error-message-inside-tdvp/2368 "2025-05-04T18:34:44Z")
Hi, I am using the tdvp function and it gives me the following error: ProjMPO-ITensor product P\*v is not equal to the order of the ITensor v. I’ve attached the full error message in the end. Note that I have not twee… --- ## [Simple circuit operations on MPS](https://itensor.discourse.group/t/simple-circuit-operations-on-mps/2341)
**Author:** [@Arnab](https://itensor.discourse.group/u/Arnab)\ **Replies:** 3\ **Last updated:** [April 9, 2025, 8:03pm UTC](https://itensor.discourse.group/t/simple-circuit-operations-on-mps/2341 "2025-04-09T20:03:27Z")
Hi, I am trying to do simple unitary circuits (MPO) on MPS . For example, I want to get a MPS representation of the states: \\displaystyle |\\Psi\_1 \\rangle =\\left\[ \\prod\_{i=1}^{N} CZ\_{i,i+1}\\right\]\\; \\ket{++\\dots +} \\d… --- ## [BoundsError: attempt to access 0-element Vector{Int64} at index \[1\]](https://itensor.discourse.group/t/boundserror-attempt-to-access-0-element-vector-int64-at-index-1/2299)
**Author:** [@zipeilee](https://itensor.discourse.group/u/zipeilee)\ **Replies:** 2\ **Last updated:** [March 15, 2025, 12:16pm UTC](https://itensor.discourse.group/t/boundserror-attempt-to-access-0-element-vector-int64-at-index-1/2299 "2025-03-15T12:16:20Z")
I encountered this error while using apply for TEBD, but I have already “grad” the sites of the MPS as described in this link. function measure\_pauli(mps::MPS, basis::Vector{Int}) psi = copy(mps) N = length(psi)… --- ## [MPS purification and MPO purification](https://itensor.discourse.group/t/mps-purification-and-mpo-purification/2283)
**Author:** [@Q-SF](https://itensor.discourse.group/u/Q-SF)\ **Replies:** 0\ **Last updated:** [March 5, 2025, 8:34am UTC](https://itensor.discourse.group/t/mps-purification-and-mpo-purification/2283 "2025-03-05T08:34:51Z")
Hi! There are two types of finite-temperature purification codes: MPO purification and MPS purification. I have four questions regarding these two codes. What I want to calculate is the dynamical structure factor of the… --- ## [MPO for Anyon Hubbard model](https://itensor.discourse.group/t/mpo-for-anyon-hubbard-model/2275)
**Author:** [@Ashinxinl](https://itensor.discourse.group/u/Ashinxinl)\ **Replies:** 11\ **Last updated:** [March 6, 2025, 6:12am UTC](https://itensor.discourse.group/t/mpo-for-anyon-hubbard-model/2275 "2025-03-06T06:12:06Z")
Hello everyone, I am trying to reproduce the results from a paper on the Anyon Hubbard model. (ImageSource:DOI: 10.1103/PhysRevB.97.115126) After defining the operators, I encountered an issue: when summing terms … --- ## [On the naive contraction implementation](https://itensor.discourse.group/t/on-the-naive-contraction-implementation/2271)
**Author:** [@VinceNeede](https://itensor.discourse.group/u/VinceNeede)\ **Replies:** 0\ **Last updated:** [February 28, 2025, 9:16am UTC](https://itensor.discourse.group/t/on-the-naive-contraction-implementation/2271 "2025-02-28T09:16:45Z")
Hello everyone, In the current implementation of the naive contraction algorithm of MPS with MPO, a new MPS is computed from contracting each tensor of the MPS with the corresponding tensor of the MPO, then this new sta… --- ## [Gauge preserving MPO's](https://itensor.discourse.group/t/gauge-preserving-mpos/2267)
**Author:** [@VinceNeede](https://itensor.discourse.group/u/VinceNeede)\ **Replies:** 2\ **Last updated:** [February 28, 2025, 8:39am UTC](https://itensor.discourse.group/t/gauge-preserving-mpos/2267 "2025-02-28T08:39:04Z")
A bit of a more mathematical/physical question. Given a Gauged MPS (let’s suppose left orthogonalized for simplicity) and an MPO, does a gauge for the MPO exist such that it preservers the gauge of the MPS? Does such gau… [Next page](https://itensor.discourse.group/tag/mpo/11.md?match_all_tags=true&page=1&tags%5B%5D=mpo)