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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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 ...
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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 ...
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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 ...
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Is Qiskit's Estimator Primitive running PauliStrings in Parallel?
I am trying to run the following code:
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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 ...
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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 ...
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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 ...
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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 $...
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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}...
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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 ...
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Pennylane variational classifier demo - need for padding
In the variational classifier demo from Pennylane, the data loading is performed with
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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 ...
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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 ...
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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:
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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 ...
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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 ...
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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 ...
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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)...
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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 ...
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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. ...
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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 ...
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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 ...
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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 ...
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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 = \...
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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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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 ...
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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 ...
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Does the gradient commute with the partial trace?
Suppose I have a parameterized quantum state: $\rho(\theta) = U(\theta) \rho U^\dagger(\theta)$. I am curious to know whether the following holds:
$\frac{\partial \text{Tr}_A (\rho(\theta))}{\partial \...
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How the number of function evaluations is calculated in Qiskit when running VQE
I want to understand how the number of function evaluation is calculated by Qiskit when running VQE algorithms. Here is some code I used in order to test this:
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N-qubit VQE ansatz to generate all states?
I have found ansatzes that generate every state for certain specific values of n. However, I want to be able to write a function where I can pass in a value n (number of qubits) and be returned an ...
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How can i get the superposition of 8 bits from 26 bits outputs in qiskit
the only idea i see is get state vector from density_matrix
for example, i have the circult:
...
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SPSA: maxiter (int) – The maximum number of iterations. Note that this is not the maximal number of function evaluations
This is from classical optimization algo. used for VQE. May I know what is the difference between maxiter and the number of function evaluation difference?
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How grouping of Pauli strings is handled in Qiskit when running VQE?
When performing a VQE algorithm, the electronic problem Hamiltonian of the physical system under study needs to be mapped to a qubit Hamiltonian written as a sum of tensor products of Pauli operators (...
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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 ...
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Combinatorial optimization problems solving using VQE
I'm studying about the variational quantum algorithms and I would like to know about the usage of VQE for solving combinatorial optimization problems.
VQE can find the ground state energy of a given ...
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Simplest 2-site VQE Ansatz to generate all states?
For 1-site I was able to use an Rx gate followed by an Ry gate to generate every possible state. For two-sites, I initially tried to apply this to each qubit but realized this doesn't work because it ...
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Error when importing qiskit_nature.algorithms.(GroundStateEigensolver, NumPyMinimumEigensolverFactory)
I'm trying to import the following elements:
from qiskit_nature.algorithms import (GroundStateEigensolver, NumPyMinimumEigensolverFactory)
But it shows the error:
AttributeError: module 'sklearn....
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BOBYQA optimizer IndexError
I'm trying to implement BOBYQA optimizer for my VQE job. Though, I'm facing the below issue. Can anyone help in pointing out what the actual cause of this issue is and how to solve this:
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Only use the specific parameters (angles) in variational quantum eigensolver
I’m following the tutorial (https://qiskit.org/textbook/ch-applications/vqe-molecules.html) to construct the VQE circuit. In this tutorial, it used the classical optimizer like “COBYLA, SPSA, SLSQP” ...
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What is the expectation value for the ground state of $ H = \sum_i Z_i Z_{i+1} + \sum_i X_i $?
What is the expectation value for the ground state of $ H = \sum_i Z_i Z_{i+1} + \sum_i X_i $ ? In Eq. 15b this provides a solution in k space. The minimum would be reached for $E = -4$. But for ...
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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 ...
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Commutativity of XY gate
My question is a simple one: Can 2 XY gates commute ?
XY gate is a 2-qubit XX+YY interaction also sometimes referred to as iSwap gate.
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How to derive quantum advantages for VQAs, if the underlying classical optimization is hard to solve?
This is probably a dumb question but here it goes:
Variational Quantum Algorithms (VQAs) are the leading proposal to derive quantum advantage use NISQ devices. VQAs employ classical optimization ...
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I am optimising a variational quantum circuit to learn a distribution $p(x)$, but it doesn't converge over a training set $\mathcal{X}$?
I am training a variational quantum circuit to learn distributions: given data $s(\vec{\lambda})$, what is the probability distribution for the parameterisation $\vec{\lambda}$, i.e. the posterior ...
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qiskit.algorithms.optimizers callback function for all optimizers
I am aware that VQE and VQC factory supports callback functions which can allow us to store intermediate values during optimization through callbacks in its arguments. However my loss function is ...
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getting error while simulating LiH using VQE
I wrote code again using updated qiskit nature libraries but I am facing error , I need help to finding solution so that we can run this code on latest version of qiskit.
I am attaching code below........
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Qiskit VQE output
When running Qiskit vqe.compute_minumum_eigenvalue() a dictionary of various values are returned.
Within this dictionary are two parameters called ...
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Evaluate a gradient with a specific backend (Qiskit)
I'm following the tutorial on gradients in Qiskit. Suppose I have the following:
...
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How VQE is scalable if the dimension of the Pauli basis of the given Hamiltonian grows exponentially with the number of qubits?
For a given Hamiltonian operator $H$, It's possible to approximate its smallest eigenvalue using VQE. Any Hamiltonian is a Hermitian operator. Therefore, for a system with $n$ qubits, the set $S$ of ...
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gradient estimations on variational quantum algorithms
Other than the two famous parameter-shift rule and finite difference method, is there any other (perhaps simple) methods to estimate gradients of a cost function in variational quantum algorithms?
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