Questions tagged [vqe]

For questions about the Variational Quantum Eigensolver, an algorithm which can find eigenvalues of large Hermitian operators.

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36 views

How to improve accuracy of ground energy values from a VQE

Using the Qiskit textbook I have been using a VQE to find the ground state energy of Hydrogen at different interatomic distances on a quantum machine. However, the average energy value I will always ...
4
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0answers
89 views

Implemented QAOA returns wrong result

I try to apply QAOA algorithm to find minimal energy state of the Hamiltonian: $H_A = \frac{1}{2}\sigma_z^1 + \frac{1}{2}\sigma_z^1\sigma_z^2$ It is expected that with p=2 my variational should ...
3
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0answers
29 views

Run VQE for parametrized quantum circuit with ancilla qubits

Let's say we have the following circuit (picture and code shown below), and now the $q_0$ is an ancilla qubit. If the system of interest has only two qubits, Is there a way to use only $q_{1,2}$ as my ...
2
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1answer
33 views

Applications of pauli operator grouping for simultaneous measurement in VQE

I have read some papers talking about Pauli operator grouping for simultaneous measurement in VQE. I was wondering can this "simultaneous measurement" approach be used in other variational ...
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1answer
30 views

Increase maximum shots on IBM Hardware when running Quantum Variational Algorithms

I am interested to know whether there is a quick and elegant way of increasing the number of shots (more than 8192 shots) on IBM hardware when running variational algorithms like VQE or QAOA. I know ...
2
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2answers
58 views

Callback function in VQE do not return the intermediate values of the parameters

I tried to save all the intermediate values of the parameters when running the built-in VQE in qiskit. The callback function can save the mean values and counts, however it seems only save the very ...
2
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1answer
43 views

Is it possible to measure “aux_operators” in built-in VQE with backend “qasm_simulator”

I am trying to measure the number operator, together with the ground state energy with the built-in VQE on Qiskit. However, if I pick the backend to be ...
4
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1answer
69 views

Expected value in a VQE qiskit

I'm learning VQE(variational quantum eigensolver) of qiskit, but I have a question about how it measures the expected value of the energy ($\left \langle H \right \rangle$). I saw in other question ...
2
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1answer
47 views

Decomposition of 2-qubit Hamiltonian into standard gate set for QAOA

I try to decompose ansatz into gate set in order to create a circuit in qiskit for QAOA algorithm. I don't understand how represent parametrized 2 qubit ansatz as circuit. $ H{_B} = \sum_{j=1}^{n} {\...
3
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1answer
95 views

Using Qiskit VQE for solving an eigenvalue problem

I am a new user of Qiskit and I believe there is a simple answer to my question but I have had a very hard time finding a straightforward answer. I am trying to transform a given $3 \times 3$ (...
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2answers
56 views

Creating a parameterized Operator in Qiskit

I'm trying to run a VQE for a specific custom Anzats. The Anzats is built up of an unitary matrix $U_H$, which I'm trying to created in this way: ...
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1answer
55 views

Recording the time taken by a VQE to find ground state energy

I want to record the time that a VQE solver takes to find the ground state. At the moment I am using: ...
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1answer
58 views

What are the main differences between the “unitary coupled cluster” and the “hardware efficient” ansatzes in VQE?

There are two popular initial states, in general, for VQEs: the unitary coupled cluster ansatz and the hardware efficient ansatz (for details, see here: https://quantaggle.com/algorithms/ansatz/). ...
2
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1answer
69 views

TypeError: 'NumPyMinimumEigensolver' object is not subscriptable

I'm trying to implement the same Jupyter notebook Jin-Sung Kim gave in his YouTube video The Variational Quantum Eigensolver — Programming on Quantum Computers — Coding with Qiskit S2E4; however, I'm ...
2
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1answer
60 views

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 has to be done, can I ...
2
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0answers
30 views

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: https://arxiv.org/pdf/1709.03489.pdf in Chapter 4.2 page 15 to 17. For ...
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1answer
34 views

Depth for UCC ansatz

I tried to understand the notion of depth vs Trotter step in a uccsd circuit for the vqe algorithm in qiskit (I use an older version, 0.15). When I tried understanding it for a small system like H2, ...
0
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2answers
52 views

How does VQE performs the measurement on a given Hamiltonian?

I'm trying to understand, given a specific Hamiltonian, for example $H = Z\otimes Z+X\otimes Z$, does the VQE algorithm calculates the expectation value of $Z\otimes Z$ first or does it calculates the ...
1
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1answer
42 views

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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2answers
47 views

How to use VQE function in Qiskit

As part of a project I'm working on, I want to use VQE algorithm to calculate the minimal eigenvalue for given Hamiltonian. I use Qiskit on IBM UI online. The Hamiltonian is given as a sum of tensor ...
1
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1answer
31 views

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 resulting eigenvalue is quite close to the expected ...
4
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1answer
125 views

QUBO, Ising Hamiltonians and VQA

I understand that usually the combinatorial optimisation problems are turned into QUBO, which has a very simple mapping to Ising Hamiltonians. Ising Hamiltonians in turn have the desired properties of ...
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1answer
54 views

An effective way to submit all the jobs for VQE/QAOA at a time to an IBMQ machine?

In Qiskit, I am solving a VRP for 5 nodes and it creates 20 variables for a QUBO. It runs in a 65 qubit machines (any machine below that many fails). Now, in such a typical solvers for optimization (...
2
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1answer
87 views

Why VQE gives an incorrect ground state energy for a chain of 4 hydrogen atoms?

I am a bit hesitant to ask this very specific question, as I feel other people need not benefit from it. But since I have struggled for a while, and I think I should get some help. So I am using VQE ...
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0answers
77 views

Wrong Expectation value when implementing a VQE for the Heisenberg Hamiltonian

I tried to implement an extended Heisenberg-Hamiltonian as an extra exercise further than my homework. My Hamiltonian is the following: $H = \sum_{NN} \sigma_x\sigma_x + \sigma_z\sigma_z$ I try to ...
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1answer
69 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 ...
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2answers
73 views

How to run VQE experiments on IBMQ Backends?

The VQE.run method only takes a quantum_instance of type QuantumInstance or BaseBackend and ...
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1answer
34 views

Why is the local qasm_simulator significantly slower than the statevector_simulator?

I've been running VQE experiments locally using both the statevector_simulator and qasm_simulator, however I've noticed that the ...
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2answers
63 views

Why is there a significant variation between the exact and VQE energy results?

When running the VQE simulation for $H_2$ over a range of distances as detailed in the Simulating Molecules using VQE section of the Qiskit Textbook, the VQE energy deviation from the exact energy ...
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1answer
68 views

Why is circuit inverse not working for EfficientSU2?

For some reason I get the following error when attempting to find the inverse of the EfficientSU2 VQE variational form: TypeError: 'NoneType' object is not ...
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1answer
58 views

On number of parameters and operators in UCCSD in qiskit

I have two questions on UCCSD in qiskit, please see the code below. ...
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1answer
60 views

Why is local qasm simulation taking so long for VQE?

I've successfully run the $LiH$ VQE simulation detailed in Simulating Molecules using VQE using the statevector_simulator, however when attempting to run the same ...
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1answer
53 views

In Variational Quantum Eigensolvers, what does “grouping Pauli operators into tensor products requiring the same post-rotations” mean?

In this paper (nature version), the authors state We group the Pauli operators into tensor product basis sets that require the same post-rotations. As a result, they have the table S2 in the suppl. ...
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1answer
132 views

XX and YY and ZZ Hamiltonians in vqe

I'm trying to implement a vqe in cirq and I have sort of a brain knot. I have a 4 qubit chain with periodic boundary condition. So in fact a 2x2 qubit grid. Now 2 of them each are coupled. How do I ...
2
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1answer
47 views

Why is the lowest energy important to simulate a quantum system?

Quantum computers promise that they will simulate complex quantum systems, and I keep hearing that finding the ground state of that system (using for example Variational quantum eigensolver) is ...
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0answers
24 views

How to construct Hamiltonian for combinatorial optimization problems and then convert into Pauli basis?

Suppose I have a portfolio optimization problem where I have to minimize, $$qx^T\sum x - \mu^Tx$$ where q is the maximum risk and x is {0,1}^n and $\mu$ are the expected returns. Now I have to convert ...
6
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1answer
187 views

Circuit for VQE Expectation Value Finding

I'm looking into the circuit for the VQE, but am stumped at how we can identify the expectation value of the Pauli series. Essentially, how do we find: $$ \langle \psi | H_i | \psi \rangle $$ Given $...
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1answer
166 views

Examples of VQE on Qiskit

I'm a quantum beginner, and I really need some examples to help me understand quantum computing. In particular, how to get the ground energy of Hubbard or using model with VQE in Qiskit. Code examples ...
2
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1answer
248 views

How to add several parameters in qiskit circuit?

I want to construct an ansatz circuit in Qiskit, so I need some parameters to act on the gates (e.g. RX(a), RY(b)). In the Qiskit tutorials I find a way to implement a parameter: ...
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1answer
38 views

How to build an ExpectationBase object?

I'm trying to wrap my head around the expectation argument in Qiskit's VQE class, so to understand it I'm trying to create an ExpectationBase object to understand ...
2
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1answer
95 views

What is the best way to handle parametric circuits in Qiskit?

What is the best way to handle parametric circuits in Qiskit? When I create a variational form like TwoLocal and then do ...
0
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1answer
50 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: ...
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0answers
59 views

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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2answers
92 views

Suppress deprecation warnings from Qiskit

I am running a standard VQE from the example shown in here https://qiskit.org/textbook/ch-applications/vqe-molecules.html, however I keep getting this output constantly (as many times the vqe runs ...
2
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1answer
80 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 ...
1
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1answer
59 views

In which situations is it hard to find an ansatz?

Looking at the single-qubit, toy example of VQE it's pretty much trivial that arbitrary X and Y rotations are sufficient to cover all of state space for our toy system. Unfortunately, the toy example ...
3
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1answer
99 views

VQE: Can I build a non-hermitian Hamiltonian with just Pauli matrices?

From the VQE paper they claim that a Hamiltonian can be expressed as a polynomial series of pauli operators (equation 1). While coding up VQE from scratch I made a function which would allow me to ...
4
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1answer
55 views

Resource recommendation on quantum simulations

I would like to know more about quantum simulations, so as to start on a few standard physical models (maybe particle in a box, harmonic oscillator, etc.) and then build up on more complex things. But ...
2
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1answer
131 views

What's the point of VQE if classical computers can solve for eigenvalues easily?

From a few VQE tutorials online I see that they normally start with something like: VQE is a way of getting a good estimate for the upper bound of the ground state of a quantum system's Hamiltonian....
2
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3answers
344 views

Creating a custom VariationalForm in Qiskit

I would like to use the built-in Qiskit VQE() function, with my own variational form. What is the proper way to define it? I was expecting ...