Questions tagged [variational-quantum-algorithms]

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VQLS behaves badly under simulation with noise

I was studying VQLS in https://qiskit.org/textbook/ch-paper-implementations/vqls.html and since I could not understand the circuit created by the new Hadamard test (...
1 vote
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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 ...
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27 views

Why are the variational parameters not changing in VarQRTE runs for TwoLocal ansatz?

Following the qiskit tutorial on Variational Time Evolution, I've changed the ansatz for VarQRTE from ansatz = EfficientSU2(hamiltonian.num_qubits, reps=1) to <...
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22 views

Qnode model gradient of inputs (not parameters!) question

I am trying to use qml to do physics informed quantum machine learning within Tensorflow. I know with TF, to get derivatives of the network's inputs (df/dx, for example), you can use with tf....
2 votes
1 answer
72 views

Truncated Qumode States and Support

I am currently running numerical simulations of a single qumode state acted upon by a parameterised unitary. The qumode state is realised as a Fock state with a fixed cutoff dimension $(d)$ and is ...
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33 views

Difference between PQCs and VQCs

I'm going through this TensorFlow tutorial on quantum machine learning. The code implements reinforcement learning algorithms based on parameterized/variational quantum circuits (PQCs or VQCs). What ...
2 votes
2 answers
733 views

What exactly are "variational quantum algorithms"?

I constantly see papers on "variational quantum algorithms" but I don't really see any explanation of what they are that are clear to me. I found out about the variational method in quantum ...
1 vote
1 answer
68 views

What's the case when parameter-shift rule does not hold?

When the parameterized unitary is of the form $e^{-i\theta V}$, where $V$ is a Hermitian operator of the unitary, we can use parameter shift rule to calculate the gradient. In this paper, it says: &...
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0 answers
22 views

How can I get the structure of the variational ansatz for VQLS?

I have got a system of linear equations $$ A|x \rangle = |b\rangle \\ A = 0.45Z_3 + 0.55I \\ |b\rangle = H_1 H_2 H_3 $$ and I would like to solve it for $|x\rangle$. I am currently trying to ...
1 vote
1 answer
68 views

Pennylane variational classifier demo - need for padding

In the variational classifier demo from Pennylane, the data loading is performed with ...
1 vote
0 answers
28 views

Outputing classification probability from the Qiskit VQC

I am new to Qiskit. For the last few days, I have been trying to train my first VQC to do some classification task. Now the VQC is successfully running but it could only output a label whenever I ask ...
2 votes
1 answer
108 views

Quantum computation of classical Fisher information

Consider a pure $n$-qubit quantum state $|\psi_\theta\rangle$ prepared by some parametrized quantum circuit. There exist well-known algorithms to efficiently estimate the quantum Fisher information ...
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22 views

Obtain specific expectation value for a variational quantum circuit via optimization process

I have a quantum circuit built using CNOT gates and RY gates. I would like to obtain a specific expectation value for an observable (e.g. $\langle Z \rangle$ of the third qubit equal to a constant C). ...
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 ...
1 vote
0 answers
53 views

Subespace Search Variational Quantum Eigensolver (SSVQE) with contraints

I am trying to reproduce this paper: https://arxiv.org/pdf/2211.02302.pdf. However, I am having problems in getting the singlet first excited state (S1). The authors in the paper, they use the SSVQE ...
1 vote
0 answers
52 views

Why EfficientSU2 in QGAN

In Qiskit's QGAN example, the parameterised quantum circuit to be trained is the EfficientSU2. I have not found any citation there on the choice of this circuit, and the only justification is that it ...
0 votes
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181 views

Qiskit Variational Quantum Regressor - Qiskit VQR

I am new to quantum machine learning and I am trying to build a VQR with Qiskit. The input and target data to my model both have shape (32,4), where 32 is the number of samples and 4 is the number of ...
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39 views

How to go from a classical LSTM cell to a quantum LSTM cell where the neural network parts in the LSTM cell's gates are replaced by quantum circuits?

The input data I have is a tensor with shape (num_samples, num_timesteps, num_features). A single datapoint in my problem case is a feature vector of dim = 4 which conceptually corresponds to an ...
0 votes
0 answers
21 views

What are the quantum algorithms available for Monte Carlo sampling?

What are the quantum algorithms available for performing Monte Carlo sampling. Is there any implementation of these algorithms. Any kind of resources would be helpful
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 ...
1 vote
1 answer
73 views

Image classification using quantum variational circuit?

Image classification using variational quantum circuit is described in here. 3 image clusters having clearly separable 3 feature coordinates have been chosen to be: There are classical clustering ...
1 vote
1 answer
120 views

Why is qiskit's VarQITE not estimating expectation correctly?

I am using Variational Quantum Imaginary Time Evolution to find the lowest eigenvalue and corresponding eigensatate of a Hamiltonian through Qiskit's VarQITE method. But, for a circuit of 4 qubits or ...
4 votes
2 answers
133 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 ...
1 vote
1 answer
38 views

Derivative of cost function with respect to the unitary matrix

Suppose I have a cost function $C = \langle \psi \rvert U^\dagger O U \rvert \psi \rangle$ for a fixed observable $O$ and a fixed state $\rvert \psi \rangle$. I know that usually people take the ...
1 vote
0 answers
56 views

an issue with the execution time of a VQC classifier on an IBM quantum machine

I tried to use the available open-source IBM quantum machines. I’m trying to do a classification using the VQC classifier to classify data, but I encountered a problem. The VQC keeps fitting on the ...
1 vote
1 answer
108 views

Getting High cost function in code implementation of VQLS pennylane tutorial

I am currently trying to implement the tutorial in pennylane https://pennylane.ai/qml/demos/tutorial_vqls.html for very complex example in 3 Qubit and cost function is very high in spite of adding ...
1 vote
2 answers
216 views

How are the parameters in a variational circuit optimized?

I'm quite new to QML and I don't understand how the parameters in a variational circuit are optimized. I read about the parameter shift rule but what happens after the gradient is calculated ? How do ...