Questions tagged [simulation]

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

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Matrix multiplication through Block Encodings

For a project, I want to simulate a matrix multiplication on a simulated quantum circuit. Assuming that we have a matrix $A\in \mathbb{R}^{m\times n}$ stored in a quantum superposition, i.e. $$|A\...
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54 views

Statevector Simulation of QAOA always finds exact solution

My question is simple: does applying QAOA with a statevector simulation always result in a perfect solution? I'm trying to calculate the best $\gamma$ & $\beta$ that solve certain problems but my ...
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Trotter error for bosons in various encodings

Mapping second-quantized bosonic modes onto qubits can be done using various encodings. Each of those have their pro et contra. Fewer qubits — more gates, and vice versa. Encoding an $N$-level bosonic ...
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48 views

Types of Quantum Computer [duplicate]

I am confused of all that different Quantum computers. please correct me if I say something wrong. There are two main different types of quantum computing: Quantum Gates based computing quantum ...
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1answer
37 views

Simulating QPE + Grover using Low-Rank Stabilizer Decomposition

I want to simulate a 40-45 Qubit circuit that applies Grover + QPE. I've tried running a simulation on qiskit but can't really go past 18 qubits on my machine. As an alternative, I've been reading ...
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1answer
42 views

Get the gates after fusion optimization in Qiskit statevector simulator

I tried to obtain the gates after fusion in Qiskit-aer statevector simulator. What I can find now is that it provides a backend option saying fusion_verbose (bool): Output gates generated in fusion ...
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1answer
40 views

noisy circuit by openfermion

I am working on designing quantum error mitigation algorithms for simulating chemical systems. Therefore, a necessary component is to add noisy to the ideal circuit when using a quantum simulator. But ...
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1answer
184 views

Q# Simulation Behavior

I am attempting to run a series of tests on a Q# program I'm running on the local simulator, but I'm not seeing any way to use >1 shot and collect the results of those shots at once, as in ...
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1answer
87 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 ...
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1answer
54 views

Applications of Quantum Computing to Economics

I have recently been interested in the field of 'Econophysics' which as I understand it is the practice of basically applying results of physics in areas such as non-linear dynamics and stochastic ...
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1answer
107 views

Job fails when using PulseSimulator: Job Status: job incurred error

I'm trying to simulate a basic circuit using the PulseSimulator in Qiskit. The following Qiskit Pulse code works when I run it on the real device, but not when ...
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1answer
101 views

Simulate a quantum channel with a certain fidelity

I am looking for an easy-to-use framework for simulating a quantum channel that can accept the desired average fidelity of the channel as input. For example, if I want a channel with 98% average ...
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1answer
93 views

Are almost-Clifford circuits almost easy to simulate?

Circuits consisting entirely of Clifford operations in $\{X, Y, Z, H, S, \text{CNOT} \}$ are "easy" to simulate classically since there is a method that can fully compute such circuits over $...
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56 views

How can I fix the BrokenProcessPool error in Qiskit?

I'm running a set of quantum circuits using the ibmq_qasm_simulator. However, sometimes my code works for the simulation, but sometimes it doesn't, and the system ...
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1answer
55 views

Trying to perform Quantum Phase Estimation on T-gate

I'm trying to perform QPE on the T-gate in Quirk but I'm not getting the correct result. For the T-gate, I should be measuring (001) with 100% probability, but instead, I'm getting the following: I'...
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1answer
167 views

Trying to understand this measurement of a simple quantum circuit

It's a newbie question, I know. But I was just wondering if someone could help me understand why this simple circuit results with the measurement shown. I've just didn't get the last step. It's not ...
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60 views

What is the non-recursive form of the sum-over-paths simulation algorithm?

In my previous question on this, I managed to come up with a simple recursive algorithm for the sum-over-paths method. However, what other snatches of material I can find online don't use recursion ...
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1answer
34 views

Is there a faster way to get 'a list of' result from 'a list of inputs'?

I had a question about obtaining the probability of a certain state from the histogram, still using this example, suppose there's a variable in my quantum circuit, it's values are stored in an 'np....
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1answer
45 views

Is it possible to construct Grover search from Clifford gates only?

In the article Is Quantum Search Pratical the authors emphasized that a complexity of an oracle is often neglected when advantages of Grover search are discussed. In the end, a total complexity of the ...
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2answers
108 views

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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59 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
50 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
131 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
37 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
73 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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4answers
65 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
332 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
77 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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48 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
48 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
56 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
122 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
51 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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106 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
63 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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1answer
35 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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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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136 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
72 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
120 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
120 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
64 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
34 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
102 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 ...
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2answers
195 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
115 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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1answer
100 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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84 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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162 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 ...