Questions tagged [simulation]

For questions about simulating either quantum computers or simulating things on quantum computers.

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What is the “sum-over-paths” picture of quantum computing?

In chapter 9 of Scott Aaronson's book Quantum Computing Since Democritus (see online progenitor lecture notes here), he introduces a strange (to me) conceptualization of applying two Hadamard-like ...
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0answers
50 views

Length / transpilation issues with Grover's algorithm

I would like to discuss the discrepancies between what we see in the simulator versus what we see in the actual running of the code on any IBMQ machine for any qubits at 5 or above. I am doing a final ...
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1answer
44 views

Computation of qubits with quantum gates using density matrix form

I'm making a quantum circuit with qubits and quantum gates. While I'm doing it, I have some problem with it. My calculation process is below. As you can see, start qubit is $|0 \rangle$ and after 'X' ...
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1answer
49 views

Qiskit “statevector_gpu” method not available

I am trying to use the statevector_gpu simulation method in Qiskit Aer (see this page). I installed qiskit-aer-gpu according to ...
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1answer
31 views

Qiskit BasicAer simulator options

I usually use Qiskit "Aer" to simulate quantum circuit with several methods such as statevector, density_matrix, ...
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1answer
43 views

Qiskit BasicAer & Aer

While I'm simulating grover's algorithm, I found that with BasicAer backend it works well but with Aer it is not. What is the difference between ...
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3answers
31 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 ...
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2answers
163 views

How is a quantum simulator able to simulate a quantum mechanical properties on a classical computer?

I'm confused as to how a classical computer can simulate quantum mechanical properties through the use of classical bits. Why do we need quantum computers if a quantum simulator can do it's job on a ...
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2answers
75 views

What is the best approach for classically simulating quantum devices?

Now I'm focusing on quantum simulation (especially on classical supercomputers), but I saw there exist so many simulators. Is there any criteria to judge which is the best? https://www.quantiki.org/...
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1answer
40 views

Inconsistency in Qiskit Aqua CircuitSampler from Operator Flow

I am trying to wrap my head around Qiskit Aqua Operators and I stumbled upon this: My code ...
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1answer
45 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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1answer
50 views

Why running time of qasm simulator is significantly smaller in comparison with quantum machines?

I ran a 3-qubit measurement circuit on QASM simulator as well as on IBM Q Melbourne, Santiago and Vigo machines. The running time on the simulator is in few milliseconds (400-800) while in the case of ...
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2answers
67 views

How to plot histogram using statevector simulator?

I'm trying to run my quantum circuit and plot the simulation result (counts) using the statevector simulator (to avoid 'shot noise'). However, instead of a 2-d histogram, the examples on Qiskit ...
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1answer
45 views

How can I print out the probability of a certain state in histogram?

This is a simulation I did in my program. I'm hoping to print out the probability of the state $|0001\rangle$ (which is $0.052$), and store this number in a letter (a). How can I do this? Thanks!!
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2answers
44 views

How to fix “QiskitChemistryError:PySCF is not installed”

I’m trying to simulate LiH using VQE. But I keep getting the error QiskitChemistryError:PySCF is not installed And I tried several ways to see whether my driver for the molecule was typed wrong. But ...
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1answer
36 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: ...
2
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1answer
23 views

Any good resources for learning about quantum networks and how to do a simulation of BB84 protocol?

I'm a communication engineering student. And I'm thinking of doing my project on BB84 protocol but I don't know where to start. As a beginner, are there any documents or tutorials about quantum ...
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0answers
24 views

Simulating a Quantum Network over a real Classical Network Using Simulaqron

I'm trying to simulate a quantum network over a real classical network using the Simulaqron framework. I know the documentations says this is possible but I am having trouble finding examples of how ...
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1answer
91 views

Preparing any superposition of fixed Hamming weight states

There exists a nice way of preparing any superposition (with real amplitudes — this is the case I'm interested in) of states $\{\ldots0001\rangle,\,|\ldots0010\rangle,\,|\ldots0100\rangle,\ldots\}$, ...
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1answer
60 views

IBMQ_Melbourne Readout error

I am trying to simulate an experiment on IBM's melbourne quantum computer and here are the results Qasm simulator : ibmq_16_melbourne: error why is there such high probability of unwanted states i....
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2answers
115 views

Why should we use density matrices to simulate quantum systems with noise?

Why we should use density matrices to simulate quantum systems with noise? I found that the any QEC circuit is included by some quantum gates just like normal cases, which means the state vector can ...
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1answer
113 views

How the simulator work?

Recently I focused on how to simulate in classical computer, and I found Qiskit offers qasmsimulator and statevector simulator. ...
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1answer
61 views

A question about how does the single qubit gate simulated in simulator?

I have found the procedure of simulation process as this picture : Image reference. So in the low-level compilers, all single-qubit gates are approximated by the universal gate set (CNOT, H, T, S). ...
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1answer
30 views

What would be the difference between using qsharp library on python vs learning the Q# langauge?

One difference of course is the syntax. But I'm guessing the idea is eventually quantum computers will be able run Q#, whereas now it uses simulations. Will code written in Python with the qSharp ...
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2answers
83 views

Why do I get positive amplitudes when I create a qiskit StateVectorCircuit from only negative amplitudes?

I am using amplitude encoding to encode my features in a quantum circuit. With this I expect to encode e.g. 32 features in five qubits. For the encoding I use qiskit's ...
4
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2answers
192 views

How does a classical computer simulate nonclassical correlations?

This may be a dumb question, if so please forgive me, it is late at night. I have learned that a classical computer can simulate a quantum computer in exponential time and space, but classical ...
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1answer
38 views

A question about how to emulate quantum states and computation on classical computer

I have understood the concept of "universal quantum gates" in real quantum computer, and the quantum gates and states can be emulated as matrix in classical computer, and the matrix operation can be ...
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2answers
100 views

How to run an approximate simulation, and why

I'm looking at the Qiskit getting started documentation, https://qiskit.org/documentation/getting_started.html. They create a quantum circuit and run an approximate simulation on it 1000 times: Why ...
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0answers
48 views

How to turn off multiprocessing in TensorFlow Quantum

Some background: I'm currently running the same training algorithm with a classical neural network and a quantum circuit, respectively. The NN is implemented in Keras with a TensorFlow backend, the ...
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1answer
71 views

Is it a good idea to publish a research paper about the simulation of BB84 protocol?

I'm an engineering student. As my end of year project I've simulated BB84 protocol using simulaqron(python). I'm thinking about publishing a paper about this simulation. I haven't published any ...
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0answers
129 views

What is the usefulness of the Suzuki-Trotter formula?

I can't seem to wrap my head around the suzuki-trotter formula. I have seen This answer but I am still confused of the applicability of the formula. Let me explain: As I understand it Trotterization ...
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1answer
54 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 ...
3
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1answer
141 views

What are the biggest obstacles currently preventing us from solving real world problems defined in terms of quantum simulation?

Quantum simulation (also referred to as Hamiltonian simulation) is defined as follows: In the Hamiltonian simulation problem, given a Hamiltonian $H$ ($2^n \times 2^n$ hermitian matrix acting on $n$...
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1answer
100 views

Problem with building quantum circuit for Hamiltonian operation

In the book, Nielsen and Chuang, there is a section on quantum simulation of the quantum search algorithm. Hamiltonion operator is defined as follows- $$ H = |x\rangle\langle x| + |\psi\rangle\langle\...
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26 views

Can We Currently Import Quantum Datasets (Datasets Containing Quantum Data) Onto NISQ-era Quantum Computers?

I'm still investigating the TFQ whitepaper. In one section of the paper, the authors say this with respect to Quantum Datasets In general, [a quantum dataset] might come from a given black-box ...
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1answer
104 views

Question Regarding Simulating Hamiltonian With Quantum Circuit

There have been a few other questions about this section of Nielsen and Chuang, but when working through the output of the circuit, there are some inconsistencies that are probably due to some mistep/...
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1answer
101 views

Can every process in nature be simulated by a Turing Machine or a quantum computer?

Given any initial condition or value A, A leads to B after a procedure of physics or nature P. Now is there any turing machine or quantum computer that can simulates P,converting A into B? In other ...
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1answer
49 views

Results of SAT on the Qiskit simulator

I computed SAT formula with the Grover search algorithm on the Qiskit simulator with default parameters, but I don't understand why the incorrect solutions don't have a probability of 0? The SAT ...
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1answer
59 views

A question about quantum circuit simulation on PC

In classical logic circuit consisting of AND, OR and others, common gates can be realized by electrnic signal. Each time cycle can run a function unit like the picture below. Now I have read many ...
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1answer
118 views

What did exactly Google do in simulating a random quantum circuit on a classical computer in supremacy experiment?

I've been working on Google quantum supremacy paper for quite some time now and I have a problem in understanding how exactly they simulate their actual random quantum circuit on a classical computer. ...
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5answers
178 views

Does a classical computer really require $2^n$ complex numbers to represent the state of $n$ qubit quantum computer?

One often reads that the key reason why classical computers (probabilistic or deterministic) are unable to simulate quantum algorithms such as Simon's or Shor's efficiently is that a classical ...
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1answer
249 views

How Mature is the Tensorflow Quantum Library [closed]

Where does The Tensorflow Quantum ( TFQ ) library fall on it's maturity curve. In other words can we currently leverage the TFQ ...
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0answers
59 views

What Are The Most Promising Real-World Applications For Quantum Machine Learning

I know this has been asked before in different ways, however, I am interested in something with a degree of clarity and focus not found in other questions. What I am looking to get is a list of the ...
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3answers
132 views

Does Planck's constant have any role in quantum computing?

I am new to the area of quantum computing, but as I study it I can't help wonder about the role of the Planck's constant. When one studies quantum mechanics one often finds statements that quantum ...
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2answers
63 views

Ansatz state for finding the lowest eigenvalue of a $2^n\times 2^n$ real matrix using VQE

I would like to find the lowest eigenvalue of a $2^n\times 2^n$ real matrix $H$ using the VQE procedure. The measurement part is simple — I just expand $H$ in a sum of all possible $n$-qubit Pauli ...
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1answer
43 views

Rotation of multi-body interaction in quantum circuit

In quantum circuit, how do you implement the rotation of multi-body interaction, such as $e^{-i\theta\sigma_z^1\sigma_z^2\sigma_z^3}$? I already know the case of less than two-body interaction, but I ...
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0answers
30 views

How to get the $T1$ specs for the Rigetti's quantum processor (Aspen 7)

I am trying to find the $T1$ coherence time for different qubits of Rigetti's quantum processor (Aspen 7) using Python. I tried using Specs() but encountered an ...
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42 views

Why Alice and Bob don't get the same result when they measure in the same basis?

I'm simulating the BB84 protocol using simulaqron. My problem is that when Alice and Bob measure in the same basis, they don't get the same result. How can I fix this error? . BB84.py ...
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2answers
189 views

Entanglement Swapping Circuit

I implemented 2 versions of the entanglement swapping circuit in IBM Q. One is using classical measurement to control X, Z gates. Another is just us C-NOT and Controlled-Z. They should be equivalent. ...
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0answers
44 views

“$W_n$ state” in Bravyi-Kitaev encoding

For a particular simulation, I need the initial (physical) state of the QC to represent the equal superposition of all single-occupancy fermionic second-quantized states. In Jordan-Wigner encoding, I ...