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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Complexity of Variational Quantum Eigensolvers

I am doing research surrounding VQE and am a bit confused about the complexity and its comparison to classical systems. My brief research has yielded me that classical eigenvalue solving is $O(n^3)$. ...
0 votes
1 answer
259 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 ...
6 votes
1 answer
1k views

VQE - How to get from expectation value to eigenvalue?

In VQE, for a single-qubit Hamiltonian, I can use a standard ansatz to make a state $\psi$ and use two products to compute the expectation value $\langle\psi|{\cal H}|\psi\rangle$. As I vary the ...
1 vote
0 answers
24 views

How to combine a VQE circuit with normal qiskit quantum circuit without parameters and give the measured set of qubits to the estimator?

I want to use a parameterized quantum-circuit which is $\text{CNOT}$ with another quantum-circuit that has no parameters, then after a series of gates on the second quantum-circuit, I want to measure ...
1 vote
1 answer
76 views

Combinatorial optimization problem via VQE instead of QAOA

I'm studying about the hybrid quantum algorithms and I have a question about the VQE and QAOA. It seems like QAOA is a part of VQE that use a certain ansatz for solving combinatorial optimization ...
3 votes
1 answer
348 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 ...
3 votes
1 answer
30 views

Prereqs for learning Variational Quantum Eigensolver (VQE)

I am trying to learn Variational Quantum Eigensolver algorithm(s) for a class. However, I am struggling because I don't understand any of the problems we are trying to solve. I want to know what I ...
1 vote
4 answers
243 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 ...
2 votes
0 answers
16 views

Running VQE code using qiskit_nature on IBM computers

$\texttt{qiskit_nature}$ no longer has the $\texttt{runtime}$ feature and $\texttt{VQEClient}$ function that was used to run a VQE code on one of the IBM computers. I could not find any easy migration ...
1 vote
1 answer
67 views

How can I Combine Qiskit's VQE Tutorial and TSP Simulator to solve the TSP on a real backend efficiently?

I have a university project where I am trying to solve the Traveling Salesman Problem by using a real quantum backend, rather than just the VQE simulator, as in this tutorial. I found this code on ...
1 vote
0 answers
61 views

Usage of qiskit API MatrixOp.to_pauli_op()

I am quite confused with the MatrixOp.to_pauli_op() API. I have a hamiltonian, and it is given as input to a API MatrixOp. ...
1 vote
1 answer
24 views

vqe.compute_minimum_eigenvalue API of qiskit produces different eigenstate results for statevector_simulator ands qasm_simulator

I am trying to understand the usage of vqe.compute_minimum_eigenvalue API of qiskit for the statevector_simulator and qasm_simulator. I am only interested in the <...
0 votes
1 answer
305 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
22 views

VQE on Qiskit: getting counts per Hamiltonian term

Consider a VQE calculation (using the QASM backend and on Qiskit) that involves a qubit Hamiltonian with, say, 5 terms. Is there a way for us to get the counts for each of the Hamiltonian terms that ...
1 vote
1 answer
25 views

Reusing Parameters for Multiple Runs with Qiskit's SPSA Optimization

I am using Qiskit's SPSA optimization algorithm to find the ground state energy of various lattices (Fermi-Hubbard model) by running different circuits through it and having the algorithm modify the ...
1 vote
1 answer
176 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}...
1 vote
1 answer
328 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
71 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
582 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
78 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
40 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
127 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
349 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
25 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
944 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
225 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
67 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
807 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 ...
2 votes
0 answers
20 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
174 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
45 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
95 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
79 views

Is Qiskit's Estimator Primitive running PauliStrings in Parallel?

I am trying to run the following code: ...
2 votes
0 answers
41 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 ...
5 votes
1 answer
653 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
213 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
118 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
61 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
69 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
193 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
66 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
67 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
103 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
184 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
109 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
28 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
132 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
228 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
58 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
415 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 ...

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