Questions tagged [simulation]

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

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How to import a generic stabilizer code in stim

I just started using stim to simulate the performance of quantum error correcting codes. I hope this is the right place to ask questions about the subject. The example code with the repetition code ...
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44 views

Random circuits with google cirq

For my dissertation I need to simulate random circuits and I have been trying to use google Cirq for that. Looking at the documentation I have seen how to create my own circuit and simulate it, but it ...
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how can i find ground state of final hamiltonian

decompose the evolution operator into a sequence of steps using the Trotter-Suzuki formula unitary operator is the evolution operator from 0 to T , k is a large integer so that τ = T /k is a small ...
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53 views

What are the evidences that quantum simulation have a future?

Here future means orders of improvement which can solve rather different problems e.g. emergent phenomenon. For example, the first integrated logic only have several transistors, now it have billions ...
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40 views

Could quantum computers answer the question of whether QCD predicts quark gluon confinement?

As I understand it, it is not known whether or not QCD actually predicts quark gluon confinement. As I understand it answering questions in quantum field theories is generally harder in terms of ...
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1answer
81 views

What is difference between qasm_simulator and ibmq_qasm_simulator?

There are many ways how to simulate a quantum circuit on IBM Q. However, in partiuclar I am interested in a difference between qasm_simulator and ...
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62 views

Accuracy of rotational gates on IBM Quantum

As a computer memory is finite, it seems reasonable to assume that a rotational angle of gates $Rx$, $Ry$ and $Rz$ (and $U1$, $U2$ and $U3$ gates as well) has some smallest step which can be ...
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70 views

Can I extract information from a single shot efficiently?

I'm running a quantum simulation and want to obtain some information from a single shot of an experiment. Here's part of the code I'm working on: ...
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2answers
174 views

What is the role of entanglement in quantum-computational speed-up?

The way I see it, there are three main quantum properties utilized in quantum computing - superposition, quantum interference, and quantum entanglement. I'm looking to understand which one is ...
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Efficient simulation of linearly assembled Quantum States

In this paper section 4.2 the author describes how to efficiently simulate linearly assembled quantum states. When describing the procedure to do so the author shows the following circuit: The ...
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119 views

Explicit states with high $T$ count

It is well known, that the Clifford $+T$ gate set consisting of the gates $\lbrace H, S, CNOT, T \rbrace$ is universal for quantum computation, that is, for any n-qubit unitary $U:\left( \mathbb{C}^2\...
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50 views

How can I simulate the Avg CNOT Error on IBMQ Backends?

I want to know exactly how to estimate the Avg CNOT Error rate for IBMQ Backends? For instance, I tried to estimate the Avg CNOT Error rate for Belem Backend; I randomly prepared the 00,01,10,11 ...
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94 views

What is the maximum number of qubits that can be simulated by Qiskit using any method?

I'm looking to write an algorithm (potentially) using Qiskit, and am trying to find out what the maximum number of Qubits is that Qiskit can support with various simulation methods. From reading other ...
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98 views

Is a black-box gate whose output is conditional on the value of an input amplitude possible?

Suppose we have a qubit in the state $|q\rangle = a |0\rangle + b |1\rangle$, and another ancilla qubit $= |0\rangle$. I wish to have the following black-box gate: ...
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49 views

Which single fixed unitary can be used to efficiently simulate arbitrary quantum circuit?

Let $|p\rangle|00\ldots0\rangle$ be an initial (basis) state, where $p$ is a binary encoding of the circuit to be simulated and zeros are the working space. We apply some fixed unitary transformation $...
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383 views

How can I specify the qubits on quantum computers that I want to use?

Suppose I have the following 2-qubit quantum circuit: ...
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71 views

How to create CNOT from an entangling gate and arbitrary single-qubit gates?

I am working on the classical simulation of quantum circuits. I know how to efficiently implement the following entangling gate, which -- in the following paper: https://arxiv.org/pdf/1803.02118 -- ...
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75 views

Why does entanglement complicate quantum simulation?

To model a single qubit one would need enough memory for $2$ complex numbers. If we have an $N$ qubit system, we would have to store $2N$ complex numbers. The general statement is that to store an $N$-...
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91 views

When and how do we use basis embedding?

It is suggested in various sources that a possible approach to representing classical data as a quantum state is simply to take the binary sequence $x$ and turn it to $|x\rangle$ (i.e., "basis ...
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81 views

Why does running my circuit on Quantum Hardware produce such unexpected resultss?

I am using Jupyter Notebook with Qiskit. I have created a program that can add two 3-bit numbers together. When I simulate this program on a qasm_simulator it works as expected and I can add any two 3-...
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112 views

What is the superop simulator in Qiskit for?

I'm trying to understand what the use case of a superop simulator would be. My understanding is that density matrix is generally more resource intensive than state vector, but it has additional ...
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71 views

How accurate are Qiskit’s unitary and Statevector simulators for very large circuits?

Background: I wrote a code that takes a Qiskit circuit C as an input and outputs a random circuit C’ such that C and C’ have the same unitaries. I tested my code using Qiskit’s Statevector simulator ...
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1answer
165 views

'Best practices' for making Stim run as fast as possible?

I'm currently testing out an error-correction surface code circuit in Stim. I've tried a 19x19 surface code over 10k rounds of syndrome extraction sampled 256 times, and this takes about 165 seconds. ...
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1answer
68 views

What is the largest reported number of qubits used in a VQE simulation?

Numerous studies have investigated the simulation of an X-qubit circuit, demonstrating the 'classical simulation supremacy' on supercomputers. X is less than 50. However, useful VQE circuits are often ...
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180 views

Measuring entanglement entropy using a stabilizer circuit simulator

I'm trying to simulate stabilizer circuits using the Clifford tableau formalism that lets you scale up to hundreds of qubits. What I want to do is find the entanglement entropy on by splitting my ...
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1answer
39 views

How do I export the rightmost state of circuit wires (qbits and cbits) in a qiskit simulation

qiskit has a quantum teleportation tutorial which winds up with this simulation code: ...
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67 views

Setting the Initial State of Density Matrix Simulation in Cirq

I am trying to use the DensityMatrixSimulator in Cirq. I want to append gates to the circuit conditional on measurements. In order to reduce computational resources, I am trying to run these ...
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199 views

Memory Requirements for Qiskit Aer Simulator

I'm trying to work out how much memory is used for simulations of different sizes using the Aer simulator. Here are my calculations: $$ \text{Number of Qubits} = n $$ $$ \text{Number of Amplitudes} = ...
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1answer
140 views

What's the state-of-the-art to calculate $|Ab\rangle$, given a matrix $|A\rangle$ and a vector $|b\rangle$ in QRAM encoding

Assuming that we have a matrix $A\in \mathbb{R}^{m\times n}$ stored in a quantum superposition, i.e. $$|A\rangle= \frac{1}{\|A\|_F}\sum_{i,j=0}^{n-1}{a_{ij}}|i,j\rangle$$ and a vector $b\in \mathbb{R}^...
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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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2answers
128 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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64 views

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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55 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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45 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
78 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
56 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
195 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
131 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
85 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
177 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
170 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
169 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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107 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
86 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
174 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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66 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
40 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
84 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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161 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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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 ...