Questions tagged [vqe]

For questions about the Variational Quantum Eigensolver, a quantum/classical hybrid algorithm that can be used to find eigenvalues of a (often large) matrix H. When this algorithm is used in quantum simulations, H is typically the Hamiltonian of some system. In this hybrid algorithm, a quantum subroutine is run inside of a classical optimization loop.

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How to solve an optimization problem that includes "continuous" variables with constrains using QAOA/VQE?

Here is the code from the previous question I asked on the same topic: How to solve quadratic programming problems with continuous variables and continuous constraints by using quantum algorithms? ...
1 vote
1 answer
321 views

Why do the qasm_simulator runtimes vary significantly for different IBMQ CouplingMap/NoiseModels?

I have been running VQE experiments locally using the qasm_simulator with actual IBMQBackend NoiseModels as shown in the Qiskit Textbook. I have noticed that the ...
2 votes
1 answer
64 views

Implementing cphase gate on IonQ through Amazon Braket

I am implementing a VQE algorithm where I need controlled phase gate as part of ansatz circuit. I am using Amazon Braket service. Ionq processor however does not support c-phase gate or phase gate. ...
2 votes
2 answers
576 views

VQE Cirq example

Is my understanding correct that in this example the Hamiltonian measurement is not performed through measuring individual Pauli operators because all its terms are mutually commuting? So, for each ...
1 vote
1 answer
70 views

Need help regarding building a custom VQE

I want to write code for a custom Variational Quantum Eigensolver (VQE) capable of computing eigenvalue(s) for non-Hermitian systems, based on this paper. I have formulated a cost function (provided ...
1 vote
1 answer
36 views

Getting a numeric result from the variational quantum eigensolver

I am confused about how the VQE is able to print out a decimal number for the ground state energy of a molecule. For example, for $\text{LiH}$, the ground state energy I get for an interatomic ...
1 vote
1 answer
109 views

Calculating state fidelity and space complexity of Minimum Eigen Optimizers (VQE, QAOA and Grover Optimizer) in qiskit

I'm a beginner in using Qiskit and my Computer Science background is not extensive. But I understand the Quantum Physics aspects of it relatively well. I solved a QUBO problem in Qiskit using VQE (...
0 votes
0 answers
324 views

Hamiltonian & QubitMappingType cannot be imported from qiskit.chemistry.core

I'm trying to implement the same Jupyter notebook in The Variational Quantum Eigensolver — Programming on Quantum Computers — Coding with Qiskit S2E4;however,I found a problem: Error: ...
1 vote
0 answers
20 views

Why is quantum annealing not used in optimization for variational quantum algorithms?

I have been learning about variational quantum algorithms and encountered that none of the articles talk about using quantum annealers for optimization of the parameters ? I have however encountered ...
1 vote
1 answer
895 views

Unable to retrieve result for Job Error during VQE simulation

I am attempting to run a VQE calculation on the 'ibmq_qasm_simulator'. The job is failing with a series of errors caused by: ...
0 votes
1 answer
224 views

QVA with local Hadamard Overlap

I am trying to implement in Qiskit the quantum variational linear solver given here (https://arxiv.org/pdf/1909.05820.pdf) with a local Hadamard overlap test and failing substantially. The cost is not ...
1 vote
1 answer
59 views

Pennylane variational classifier demo - need for padding

In the variational classifier demo from Pennylane, the data loading is performed with ...
7 votes
1 answer
726 views

How can I run a VQE on one of IBMQ's Quantum Computers

I have implemented a VQE based on Qiskit's VQE function and want to run that on an actual quantum computer. My understanding was, that an IBMQ backend can be passed into the function as a Quantum ...
0 votes
1 answer
171 views

How to assign new parameters to an existing quantum circuit?

Say I have a quantum circuit like this This is an ansatz for solving linear equation provided in the Qiskit's textbook In the textbook, it was shown how to find the optimal parameters of this ansatz ...
3 votes
1 answer
345 views

VQE jobs do not appear in queue

I am trying to calculate the ground state energy of some simple molecules using 'MolecularGroundStateEnergy' tools in qiskit. When I run the calculations for very small molecules (e.g. H2, HeH+) the ...
2 votes
0 answers
19 views

Understanding the Role of Qiskit's VQE Code in Light of Pre-calculated Zero-Point Vibrational Energy in Gaussian Files

In the context of quantum computational chemistry, the Qiskit VQE (Variational Quantum Eigensolver) code is often used to calculate the vibrational energies of molecules, including the zero-point ...
5 votes
2 answers
171 views

Why is it hard to prove complexity bounds for variational algorithms?

I'm not very familiar with variational algorithms, but I've heard people say that they're "heuristic" and it's difficult to measure their performance via complexity analysis. Why is this the ...
3 votes
0 answers
44 views

How to update angles

I am struggling to understand the concept of updating angles in a parameterized algorithm. Assume I have an objective function $x^2+1$ that I want to optimize using QAOA which can handle continuous ...
2 votes
0 answers
93 views

Save output, wavefunction file and orbital information in Qiskit

I am going through LiH ground state energy calculation. I would like to know how to save the output file in Qiskit as one would do in classical computing using software like Gaussian or Psi4. Can ...
1 vote
1 answer
71 views

Is Qiskit's Estimator Primitive running PauliStrings in Parallel?

I am trying to run the following code: ...
0 votes
1 answer
288 views

How can I get the counts, as well as the solution bitstring from Qiskit VQE?

I just set up a Qiskit VQE algorithm and calculated the eigenstates. However, I'm searching now, how to show up the final, most likely solution-bit-string. And/or to print the counts. I actually ...
2 votes
0 answers
34 views

Qiskit noisy FakeManila simulator + ZNE

I am trying to run a simple VQE calculation on H2 using FakeManila noise model and ZNE for error mitigation; see code below. The problem is that I can never reach not even close the ground electronic ...
2 votes
1 answer
153 views

Knapsack problem formulation

I would like to use a knapsack problem formulation based on Lucas paper. Namely, I try to implement the following math formula for Hamiltonian $H =H_A + H_B$, where $$H_{B} = -B\sum_{i=1}^{n}v_{i}x_{i}...
5 votes
1 answer
623 views

Simulation of a helium molecule using Qiskit

I am trying to compute the ground state energy of He-He using VQE. For this purpose I have utilized Qiskit and have written the following script: ...
0 votes
1 answer
195 views

Remove Orbitals in FreezeCoreTransformer (qiskit)

In Qiskit's VQE tutorial, the FreezeCoreTransformer is used and some orbitals are removed. In the particular case of LiH, they remove [-2,-3] orbitals. Why are the orbitals indexed in this way? How ...
4 votes
0 answers
105 views

Variational Quantum Eigensolver (VQE) by scipy minimize in cirq does not work

I tried to make a cirq program calculating an eigenvalue of the observable by VQE. Inspired by the qulacs VQE tutorial, I defined a cost function from the expectation value of the observable with ...
2 votes
0 answers
57 views

Efficient gate executing the time evolution of a Hamiltonian using Runge-Kutta method

You can find a minimal working example below. In particular, I want to replace the scipy.linalg.expm() matrix exponential by a Runge Kutta time evolution method as ...
1 vote
0 answers
58 views

Help me to find error in finding Cost Function for SSVQE algorithm [closed]

Q: Build SSVQE's cost function using the following observable: $$O=2II−2XX+3YY−3ZZ\,.$$ This cost function should take in parameters as input. Use the included variational form, with reference states $...
3 votes
2 answers
156 views

The importance of the ansatz in VQE algorithm

Let's say I have a universal quantum computer that can perform anything. In this case, any VQE algorithm can use any operation, so no ansatz is needed to implement it. My question is, is the usage of ...
4 votes
0 answers
65 views

Ansatz for VQE demonstrating Quantum Advantage

What would be a possible ansatz quantum state in VQE (variational quantum eigensolver [1]) that would demonstrate the quantum advantage of VQE over classic computers? More specifically, I see that VQE ...
4 votes
0 answers
51 views

Difference between Qiskit and Openfermion two body integrals

I am struggling with understanding the differences between OpenFermion and Qiskit libraries when it comes to Molecular Data, two body integrals. For example, I am working with the following ...
3 votes
0 answers
86 views

Minimum working example for Qiskit's AdaptVQE

I am trying to implement a simple AdaptVQE in Qiskit. Following the documentation provided by Qiskit, this should be very simple: ...
7 votes
2 answers
175 views

Quantum annealing - studies showing empirical evidence for better performance in comparison with classical computers

Currently, it is not known wheter quantum anneling or algorithms like VQE and QAOA for general purpose quantum computers bring about any increase in computational power. However, there are some ...
5 votes
1 answer
103 views

Recent experimental demonstrations of variational quantum algorithms?

I am interested in the recent experimental demonstrations of variational quantum algorithms. Can someone please provide me with a list of references of recent experimental demonstrations of ...
0 votes
0 answers
27 views

Does ScipyImaginaryEvolver in qiskit work independently of ansatz and parameters?

I am solving a Hamiltonian using imaginary time evolution and I tried it with VarQITE and ScipyImaginaryEvolver available in qiskit. I created a custom ansatz so that the evolved state revolves only ...
4 votes
2 answers
124 views

Is there a way I can create an ansatz such that the number of 1 is same in all the superposition states? [duplicate]

So I am working with a variational quantum algorithm and I realised that it would be very beneficial if I could create an ansatz where all the states in the superposition have same numbers of 1s. For ...
3 votes
1 answer
218 views

What does the identity operator represent when computing $\langle\varphi|I\otimes Z|\varphi\rangle$?

Consider a single qubit state $|\varphi\rangle$ and a hamiltonian $H = Z$. Evaluating $\langle \varphi | H | \varphi \rangle$ corresponds to a measurement of $|\varphi\rangle$ in the computational ...
0 votes
0 answers
55 views

Compute molecular vibrational energy of CO2 molecule using VQE

I have to compute the molecular vibrational energy of CO2 molecules using VQE, but I am not progressing; Code on the qiskit website does not work. Does anyone have any working code to find vibrational ...
1 vote
2 answers
389 views

Expectation value of Pauli strings for VQE

I am studying VQE and have boiled it down to a matter of determining the expectation value of Pauli strings: $$\langle H \rangle = \sum_i \alpha_i \langle\psi|\hat{P_i}|\psi\rangle.$$ I have been ...
1 vote
0 answers
24 views

Is there a way to find the computational resources required to perform a simulation of n- qubits in Cirq similar to qsim?

I’m trying to model basic spin chains in 1D using VQE (ideal circuit) with cirq and qsim. The models have between 10-20 sites and varying interactions (nearest neighbour, next to nearest neighbour etc)...
0 votes
1 answer
140 views

qiskit-nature accessing circuit

There are some very nice examples on how to handle circuits using qiskit. However, once we get to the qiskit-nature documentation, it feels like a complete new world for the untrained eye. I am ...
1 vote
0 answers
36 views

Efficient classical simulation technique to execute this specific quantum circuit

I have a quantum circuit similar to the ones used in VQE methods. One difference is that the angles of the $R_y$ rotations are limited in the range $[0, 0.2]$ (and chosen randomly). In my case, I have ...
1 vote
0 answers
86 views

VQE for Vibrational ground state energy

I was reading this article. In this article, they calculated the vibrational energy of CO2 and NH3 molecules using VQE, and I checked qiskit documentation for finding Vibrational energy using qiskit. ...
0 votes
2 answers
1k views

Help on PySCF library

I am a student and I am trying to use qiskit nature in order to calculate the ground state energy of a molecule. My probelm is that when I try to run the simulation an error message comes out: ...
0 votes
1 answer
31 views

Recovering phases in $2n$-bit binary representation of n-qubit Paulis

I am currently going through a paper discussing Pauli sampling strategies for VQE: https://arxiv.org/abs/1908.06942 I want to code and test their strategy. They explain how to create a circuit ...
1 vote
0 answers
59 views

Ground state returned by VQE is not an eigenstate?

With my VQE algorithm, I want to obtain both the ground state energy and its corresponding ground eigenstate. However, the state I reach using VQE is usually very different from the true ground ...
1 vote
2 answers
194 views

Where can I find tutorials on quantum variational algorithms?

I am interested in learning about quantum algorithms, especially quantum variational algorithms. I would like to know where I can find resources that delve into specific quantum variational algorithms ...
0 votes
3 answers
317 views

How to represent Beam-Splitter and Kerr gates as basic quantum logic gates?

I want to know how to convert these exponential forms to tensor products of well known logic gates (like the ones built into Qiskit). My goal is to program the Beam-splitter-Kerr ansatz circuit for ...
3 votes
1 answer
292 views

How does VQE work?

Here is the VQE overview from Peruzzo et al. 2013 I am trying to understand in detail how each step works, assuming at first one qubit and a Hamiltonian of the form: \begin{equation}\tag{1} H = \...
0 votes
1 answer
38 views

Creating a parameterized Operator in Qiskit that cannot be decomposed into Qiskit supported gates

I am trying to create a custom ansatz to use the built-in Qiskit VQE() function. My ansatz is composed of single qubit gates and a hamiltonian gate which cannot be decomposed into Qiskit supported ...

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