Questions tagged [chemistry]

For questions regarding (or related to) applications of quantum information theory in chemistry or applications of chemistry in quantum computing.

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Number of Qubits Required for Simulation of Caffeine and Penicillin Molecules

I recently read this report from BCG, which stated: For scientists trying to design a compound that will attach itself to, and modify, a target disease pathway, the critical first step is to ...
Greenstick's user avatar
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10 votes
2 answers
688 views

Quantum Chemistry and Quantum Computing

Predicting the energy of molecules to high accuracy during the course of a chemical reaction, which in turn allows us to predict reaction rates, equilibrium geometries, transition states among others ...
user3483902's user avatar
9 votes
1 answer
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Quantum chemistry: references

I have heard about Quantum chemistry as one of the main applications of quantum computers. However, I have not found concrete related articles with circuit-implementations for these applications. ...
nippon's user avatar
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9 votes
1 answer
293 views

Impact of ordering Hamiltonian terms for Trotterization

In Trotterization, the typical Hamiltonian considered is: $$ H = \sum_{p, q} h_{pq} a^{\dagger}_p a_q + \sum_{p, q, r, s} a^{\dagger}_p a^{\dagger}_q a_r a_s $$ Which is then converted into a sequence ...
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8 votes
3 answers
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If a Hamiltonian is quadratic in the ladder operator, why is its time evolution linear in the ladder operator?

How can one show that $\hat{U}^\dagger\hat{a}\hat{U}$ (with $\hat{U} =e^{-i\hat{H}t}$) involves only linear orders of the ladder operator, when $H$ is the general quadratic Hamiltonian $(\hat{H} = \...
heromano's user avatar
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Roughly speaking, How many qubits will be needed to study (or simulate) a molecule such as: C29H31N7O?

It is often said that one of the early applications for Quantum Computers will be drug discovery. Q: Roughly speaking, How many qubits will be needed to study (or simulate) a molecule such as: $C_{29}...
david's user avatar
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7 votes
1 answer
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What are some current applications of Quantum Computing in drug discovery? Are there any test examples of this?

I am interested in applying the power of Quantum Computing to drug discovery. Although I realize that quantum computing is limited in regards to modeling drug-like compounds and their interactions ...
Rob James's user avatar
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6 votes
1 answer
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Developing quantum circuits for specific quantum chemistry configurations

I am interested in learning more about the following: would it be possible for me to simulate a molecule consisting of copper ions through a quantum circuit? And if so, can that circuit allow me to ...
Enrique Segura's user avatar
6 votes
1 answer
102 views

Do we know anything about the computational complexity of the exchange-correlation functional?

Density functional theory is based on the Hohenberg-Kohn (HK) theorems and aims to compute the ground-state many-body wavefunction of a physical material and/or molecules. To put it simply, the HK ...
Dr. T. Q. Bit's user avatar
6 votes
1 answer
534 views

Defining qubit operator from scratch

I'm a beginner with Qiskit and the Python language at all. Here is my question: One of the VQE function arguments is qubit operator (qubitOp). I saw some examples ...
Alex Tarantul's user avatar
6 votes
1 answer
358 views

Use one_body_integrals to know which orbitals to freeze in ElectronicStructureProblem

In exercise 5 of the this year's IBM Quantum Challenge, you need to use the FreezeCoreTransformer (along two_qubit_reduction and ...
epelaez's user avatar
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5 votes
1 answer
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Molecular orbitals in Qiskit

During the same minute as asking this question, I also asked this at Matter Modeling SE. In Qiskit, each qubit corrrespond to one spin orbital. For example, the $\text{N}_2$ molecule have 10 molecular ...
ironmanaudi's user avatar
5 votes
1 answer
232 views

Is VQE or one of its variations enough to help with medicine development?

One of the reasons quantum computing is often hyped in media is because of how it'll help with vaccine and medicine development. For example, this article in Financial Express and this other in ...
epelaez's user avatar
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5 votes
1 answer
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What set of quantum logical operations can one use to benchmark spin Hamiltonians?

Chemistry background: In magnetic molecules, it is sometimes the case that one can adjust the time-independent Hamiltonian by chemical design. This means there is freedom to adjust parameters in the ...
agaitaarino's user avatar
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5 votes
1 answer
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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: ...
user14660's user avatar
4 votes
3 answers
115 views

Why does joint ground state not change under action of beam splitting unitary operator?

How can one show that $\hat{U}|00\rangle=|00\rangle$ where $\hat{U}=e^{-igt(\hat{a}^\dagger_2\hat{a}_1+\hat{a}^\dagger_1\hat{a}_2)}$ and $|00\rangle$ is the unique joint zero eigenstate of the ...
heromano's user avatar
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4 votes
2 answers
429 views

Fermionic occupation operator and nearest neighbor Fermionic hopping interaction as a qubit operator

How to express Fermionic occupation operator $(\hat{a}_j^\dagger\hat{a}_j)$ and nearest neighbor Fermionic hopping interaction ($H_h= J\sum_{i=1}\hat{a}_i^\dagger \hat{a}_{i+1}+\hat{a}_{i+1}^\dagger \...
heromano's user avatar
  • 525
4 votes
1 answer
271 views

Electronic structure calculations and the Ising model: practical?

I was reading this paper which introduces a mapping from a qubit Hamiltonian to an Ising model. Firstly, the first step of the mapping seems to assume that we know an eigenstate of the system (correct ...
cnada's user avatar
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4 votes
1 answer
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If you had a 1000 qubit NISQ machine with arbitrary connectivity, what would you do?

Many current devices are constrained to nearest neighbor connectivity or small system sizes, but suppose that a NISQ machine with 99-99.5% level two-qubit gate fidelities and arbitrary connectivity ...
shixian105's user avatar
4 votes
1 answer
489 views

Is molecule simulation by quantum computing critical for drug discovery?

It is often said that the molecule simulation for drug discovery will be one of the most important applications of Quantum Computing (QC). As we all know that the entire process of new drug discovery ...
david's user avatar
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4 votes
2 answers
317 views

How do I identify a VQE job run in real hardware?

I am running a VQEUCCFactory for H2 on a real hardware device. ...
bjail66's user avatar
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4 votes
0 answers
51 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 ...
Eugen's user avatar
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3 votes
1 answer
165 views

Efficiently compute $\langle 0^{\otimes n} | e^{iA} H e^{-iB} |0^{\otimes n} \rangle$ in Qiskit

From this SE question and this Qiskit tutorial, I understand how to compute the expectation such in the form of $\langle \psi|H|\psi\rangle$ or $\langle 0^{\otimes n} |e^{iA} H e^{-iA}|0^{\otimes n} \...
Firepanda's user avatar
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3 votes
1 answer
59 views

Primer for learning about quantum circuits simulating systems

I am interested in a couple of books or arXiv links to learn how to develop quantum circuits for the purpose of simulating quantum multi-body systems. Moreover, I am interested in learning how to ...
Enrique Segura's user avatar
3 votes
1 answer
487 views

How to construct a parameterised UCCSD ansatz?

I want to try the UCC ansatz for problems other than quantum chemistry. For that I want to 'extract' the UCC ansatz (say from Qiskit) and supply it to my own VQE: I need a parameterised circuit where ...
quantum's user avatar
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3 votes
4 answers
135 views

Where can I get circuits of interest to quantum chemistry to try and simplify?

I am a computer science undergraduate working on a project in simplifying quantum circuits (using the ZX-calculus). I was hoping to try to simplify some circuits of interest rather than randomly ...
shashvat's user avatar
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3 votes
1 answer
81 views

Rabi oscillations with different energy differences

Please check this Rabi oscillations image1: Now, let's say I want to create a superposition of E1 and E2, so I started an EM field tuned to a frequency related to E2-E1. But, let's say there is ...
Tech Solver's user avatar
3 votes
0 answers
43 views

Updating qiskit.chemistry.core.Hamiltonian to qiskit-nature Framework

I recently saw a piece of code that computes molecular bond energy with respect to bond length. I am trying to update the code to the newer qiskit framework (I'm running qiskit 0.45.1 and ...
ScientiaNatura's user avatar
3 votes
0 answers
37 views

Advantage of quantum computers over classical computers in fully modeling interactions between atoms?

I'm trying to better understand the advantage quantum computers offer in terms of their ability to more accurately model chemical reactions. As a way to come to a deeper understanding, my question is: ...
Poe's user avatar
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3 votes
1 answer
279 views

What is the convention of indices for the one and two-body integrals in qiskit

I was able to calculate the one and two-body integrals for the H2 with the following code ...
fagd's user avatar
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3 votes
1 answer
345 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 ...
Joshua's user avatar
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3 votes
0 answers
171 views

How to apply unitary coupled cluster to a spin problem?

I understand how to apply UCC to a problem formulated in a second-quantized (fermion) form: you start with some state and then create a unitary operator out of single-body (or double-, triple- and so ...
Alexey Uvarov's user avatar
3 votes
0 answers
35 views

Can one make NV centred type qubits from analogus materials in the periodic table?

Can one replace Nitrogen with Phosphorus and Carbon with Silicon and so on? What would be the conditions that would preclude such a realisation? Are there any implemenations so far?
Tejas Shetty's user avatar
3 votes
0 answers
49 views

Spin precession using a laser

According to Christopher Monroe: "Modular Ion Trap Quantum Networks: Going Big", the hyperfine states of the valence electron in the Yb+ is used as a qubit. I know that we can change the spin ...
Tech Solver's user avatar
2 votes
2 answers
831 views

Why does Parity mapping allow 2 qubit reduction?

when mapping from fermionic to qubit hamiltonian, using Parity mapper allow us to reduce 2 qubit in the final hamiltonian. I would like to understand which kind of symmetries are being used and how it ...
bjail66's user avatar
  • 155
2 votes
1 answer
338 views

No. of bits in 160 qubits computer [duplicate]

I read in a book that (https://hub.packtpub.com/quantum-expert-robert-sutor-explains-the-basics-of-quantum-computing/) 160 qubits (quantum bits) could hold $2^{160} \approx1.46\times 10^{48}$ bits ...
Manu Chadha's user avatar
2 votes
1 answer
248 views

From general Hamiltonian to Ising Hamiltonian

I would like to convert my qubit hamiltonian fom the HeH+ system that I have obtained using Qiskit to an Ising or QUBO model. I have seen multiples examples from QUBO to Qubit Hamiltonian but on the ...
bjail66's user avatar
  • 155
2 votes
1 answer
772 views

How is the Hartree accuracy calculated between the exact and VQE results?

In the Simulating Molecules using VQE section of the Qiskit textbook it states an accuracy of $0.0016$ Hartree between the exact and ...
MShakeG's user avatar
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2 votes
1 answer
203 views

Logical vs Physical Qubits for Quantum Chemistry DFT

How many physical qubits are required per logical qubit in a typical Density Functional Theory implementation for a large number of atoms?
user23301's user avatar
2 votes
1 answer
916 views

How to calculate the Hartree-Fock energy in Qiskit?

I am wondering how to calculate the Hartree-Fock energy efficiently using Qiskit. For one can get the Hartree-Fock state efficiently in Qiskit, however, it seems that it is not so obvious to get the ...
ironmanaudi's user avatar
2 votes
1 answer
462 views

Fermionic commutation relation using Jordan-Wigner transformation

How can one show in detailed steps that Fermionic annihilation and creation operators, under Jordan-Wigner transformation, satisfy the Fermionic commutation relations? The Fermionic commutation ...
heromano's user avatar
  • 525
2 votes
1 answer
242 views

Qiskit - nuclear repulsion energy derivative

I know a function in PSI4 computing a nuclear repulsion energy derivative located in psi4.core.Molecule. Is there a possibility to access such function from Qiskit interface? By this "interface&...
Eenoku's user avatar
  • 255
2 votes
1 answer
494 views

Add FreezeCoreOrbitals on ElectronicStructureProblem

I want to freeze core orbitals of my molecule and I know ElectronicStructureProblem has the possibility (es_problem = ElectronicStructureProblem(driver=driver, q_molecule_transformers=...
bjail66's user avatar
  • 155
2 votes
2 answers
484 views

Need some help with simulating molecules with VQE

I have studied the example of the simulation of LiH molecule in Learning Quantum Computation using Qiskit. It is available on this link: https://qiskit.org/textbook/ch-applications/vqe-molecules.html#...
Antonio Sannia's user avatar
2 votes
1 answer
261 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 ...
LouisL's user avatar
  • 61
2 votes
1 answer
438 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 ...
fagd's user avatar
  • 940
2 votes
1 answer
269 views

Modifying Qiskit Hamiltonian

I'm fairly new to the Qiskit API. I was wondering if I could get some assistance with trying to implement our technique of projecting out a new Hamiltonian from the ground-state Hamiltonian. The ...
Stefan's user avatar
  • 21
2 votes
1 answer
341 views

What are the rules that map the second-quantized fermionic Hamiltonian into spin-form in OpenFermion?

We can use OpenFermion to get the molecular Hamiltonian in the form of: $$H = \sum_{pq} h_{pq} a_p^\dagger a_q + \frac12 \sum_{pqrs} h_{pqrs} a_p^\dagger a_q^\dagger a_r a_s$$ and we can also use the ...
刘环宇's user avatar
2 votes
0 answers
36 views

How to define an energy function, for predicting protein structure in quantum computing? [closed]

Let q denote a particular configuration of the protein in a grid, written in the form where $x_i$ and $y_i$ are the $x$ and $y$ coordinate of the $i$th amino acid. For this configuration, how to ...
Pretty's user avatar
  • 21
2 votes
0 answers
19 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 ...
Akash Yadav's user avatar