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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VQE for Max-Cut: Low Approximation Ratio (0.2 - 0.5) Instead of Expected 0.7 - 0.9
I am working on implementing a Variational Quantum Eigensolver (VQE) to solve the Max-Cut problem. I am using the approximation ratio (AR) as the metric to quantify the results, which is typically ...
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Variational quantum eigensolver tutorial
I am looking some good paper and coding tutorial for variational quantum eigensolver.
It would be great if someone can guide me on this?
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Why is the VQE insensitive to noise?
I was going through the Grove documentation on the Variational Quantum Eigensolver. In one of the demonstrations with noisy gates, it is seen that the resulting eigenvalue is quite close to the ...
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Trying to run a VQE problem on Qiskit runtime
I am trying to find the ground state of a LiH molecule using qiskit runtime instead of the Estimator primitive. I am basically using the exact code given in the documentation here as a trial. But ...
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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 ...
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How to implement the Mixer of Quantum Alternating Operator Ansatz for Max-Independent-Set
I am trying to implement the Mixer of the Max-Independent Set from The Quantum Alternating Operator Ansatz from this paper (arXiv) in Chapter 4.2, page 15 to 17.
For every verice $v$ in the Graph this ...
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Measuring Pauli strings using generators
I am trying to find the ground state of a Hamiltonian using VQE. I have decomposed the Hamiltonian into a set of Pauli strings. To decrease the number of actual measurements that have to be done, can ...
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How transform a trial variational wave funtion to an appropriate ansatz for VQE?
I have a trial wave funtion as follows:
$$\psi_{trial}=e^{-\alpha r-\beta r^2}$$
where $\alpha$ and $\beta$ are the variational parameters. It gives precise results for a specific system. Now I want ...
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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 ...
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How to calculate $\operatorname{Var}[H]$ in the context of VQEs?
Given a Hermitian operator $H$, I can calculate the variance of the Hamiltonian ${\rm Var}[H]$ as
$$ {\rm Var}[H] = \langle H^2 \rangle -\langle H \rangle^2 $$
Now, $H$ can be decomposed as
$$ H = \...
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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 ...
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How to use a customized trial wave function in a VQE algorithm?
I'm a beginner in quantum computing, so my question may seem simple. I have a quantum chemistry problem (obtaining ground state energy) in hand that I have already solved it using different standard ...
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The number of qubits of the ansatz does not match the operator
I am trying to run my below code on FakeSherbrooke() system, but I am getting an error as shown below:
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Gradient of energy in ADAPT-VQE algorithm
In the ADAPT-VQE algorithm (see https://arxiv.org/pdf/1812.11173), step (5) involves measuring commutators of the Hamiltonian with each operator in the operator pool to get the gradient of the energy ...
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VQE applications which use the Pauli strings containing {I, X, Y, Z}
VQE is a quantum-classical hybrid algorithm which goal is to find the ground state of a Hamiltonian. The most well-known application of VQE is for chemistry simulation. A chemistry simulation can be ...
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How to check if the diagonalizable circuit really diagonalizes the measurement observable?
For a Hamiltonian composed of a list of weighted Pauli strings, to calculate the expectation value, we need to obtain the expectation value of each Pauli string. To reduce the measurement overhead, ...
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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 ...
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Interpretation of output for Portfolio optimization program
I am new to quantum computing, though I am by now familiar with certain jargon but have miles to go before I gain a foothold on the subject. I have been trying very hard to understand and interpret ...
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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 ...
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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 ...
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How to know state corresponding to -1 or 1 for multi qubits VQE?
I was hoping someone can explain to me how to get -1 and 1 for a 2-qubit VQE with $\langle XY\rangle$, since we have 4 states $|00\rangle,|01\rangle,|10\rangle,|11\rangle$? For the case of 1 qubit, it ...
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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 (...
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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)$. ...
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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:
...
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How to prepare Unitary Coupled Cluster ansatz for VQE in a circuit?
I have read the following paper by Dumitrescu et al.
To make a Unitary Coupled Cluster (UCC) ansatz, one prepares with the following equation.
$$
| \psi_{\rm{UCC}} \rangle = U(\theta)|\mathrm{HF}\...
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Convexity of cost function in quantum machine learning
I have a small confusion regarding convexity of the most typical cost function considered in many QML papers: $\text{Tr}(\rho O)$, where $O$ is a Hermitian operator and $\rho$ is a quantum state. This ...
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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 ...
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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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SparsePauliOp' object has no attribute 'primitive_strings' warning for a max-cut problem using QAOA and MinimuEigenOptimizer
I am using Qiskit to implement QAOA for a max-cut problem. I am using inbuilt qiskit implemetation of QAOA and, the MinimuEigenOptimizer. The MinimuEigenOptimizer.solve() throws the warning.
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Does anyone have an idea about the execution power of IBM summit for VQE? I'd appreciate sources of papers as well for supercomputer execution
I'm trying to find the execution power of VQE in super computer and I want to know the factors of execution such as iterations, shots, convergence, etc. Please help me and also, I'd appreciate if ...
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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:
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Expectation values with finite number of shots with qsimcirq
I was using qsimcirq for VQE to obtain exact expectation values of the energy for a certain Hamiltonian with
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Portfolio Optimization with VQE (Qiskit)
I'm working on a portfolio optimization problem using Qiskit and I'm encountering an error when trying to solve a quadratic program using MinimumEigenOptimizer with SamplingVQE (V1 Primitives). Any ...
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Portfolio Optimization with VQE
I'm working on a portfolio optimization problem using Qiskit and I'm encountering an error when trying to solve a quadratic program using MinimumEigenOptimizer with SamplingVQE. Any insights on what ...
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Changing the Basis
I am attempting to use a VQE algorithm to find the ground state of a deuterium nucleus by applying a constructed hamiltonian to an ansatz state with one parameter created by a circuit. While I am ...
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Unable to use iSWAP in Qiskit TwoLocal entangling_block
I would like to use a general entangler in the entanglement_block of the TwoLocal function. The function seems to work with 'cz', 'cx', 'swap' gates, but it fails for 'iswap' gate. Below is the error ...
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Variational Quantum Linear Solver
I'm studying quantum computing right now and trying to implement variational quantum linear solver to solve a system of linear equations. From what I have understood from the paper written by Carlos ...
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Do encoding schemes for variational algorithms apply to annealing methods (e.g. DWave)?
I understand there are some efficient encoding schemes for variational algorithms, that attempt to approximate the variational state using fewer qubits. I'm thinking of 2 papers in particular, which ...
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Intuition behind the construction of an ansatz circuit
I'm learning about the VQE algorithm. When I looked at the declaration in Qiskit I saw you need to pass an ansatz which prepares the state. I looked at some commonly used ansatz functions, e.g. ...
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Using Orbital Optimization VQE
How can I use the OrbitalOptimuzationVQE class in qiskit? I want to find the ground state energy if different molecules using OOVQE but I cannot import the orbital optimization vqe class from qiskit. ...
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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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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 ...
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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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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 ...
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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 ...
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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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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 ...
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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.
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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 <...
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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 ...
