Questions tagged [simulation]

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

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How to generate a SWAP of $N$ qubits?

I know that SWAP2 (swaps 2 qubits) gate looks like: $$ SWAP2=\begin{bmatrix} 1 & 0 & 0 & 0 \\ 0 & 0 & 1 & 0 \\ 0 & 1 & 0 & 0 \\ 0 & 0 & 0 & 1 \end{...
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1answer
37 views

How do I apply a controlled gate to specific qbits in the register?

Say, I have a specific scheme, where I need to specify inputs for controlled R logical gate, which here is $$ R(\theta)=\begin{bmatrix} 1 & 0 & 0 & 0 \\ 0 & 1 & 0 & 0 \\ 0 &...
3
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1answer
128 views

How is the precision of a quantum simulation algorithm actually proved?

The problem of quantum simulation can be formulated as follows: Given a Hamiltonian $H$ ( $2^n \times 2^n$ hermitian matrix acting on $n$ qubits), a time $t$ and maximum simulation error $\epsilon$,...
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1answer
142 views

In qiskit, doing 2 subsequent measurements of a Hadamard gate on the same qubit always gives 0 on the 2nd one

When I execute the following circuit, I expect that in both classical registers, the content is identical. ...
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1answer
128 views

Can my MatLab code be used as a good simulator of a quantum computer?

I have tried to program universal quantum computer simulator in MatLab. Please find a code here: https://www.mathworks.com/matlabcentral/fileexchange/73035-quantum-computer-simulator Can be this ...
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0answers
36 views

What is the current research status in simulating many-particle systems from first principles?

There is a huge gap between basic physical laws and predicting many particle systems from first principles. It will be so amazing if we can predict most properties of many particle systems (from mass ...
4
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1answer
79 views

How to selectively apply noise in Qiskit simulations?

In Qiskit it is possible to specify noise models to apply to simulations. This allows noise to be defined for certain operations, like measurement or each type of gate. Is it also possible to change ...
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0answers
68 views

What is the cost of implementing the Quantum Fourier transform in a classical computer?

What is the cost of implementing the Quantum Fourier transform (QFT) in a classical computer? We know we require at least $\log{n}$ depth quantum circuits to do a QFT in a quantum computer, with $n$ ...
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0answers
15 views

Quantum Simulation Of Tunneling in Small System

how a single Pauli z-gate (on particular qubit) on the highest order qubit realize square well potential? How upon acting same gate on the second highest qubit, realize double square well potential? ...
2
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1answer
71 views

Can we simulate quantum many-body systems with IBMQ Experience?

Consider physical systems such as electrons in metals, or Bose-Einstein condensates, or any crystal, which are realised in the real three-dimensional space. If we want to simulate these systems on a ...
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0answers
99 views

Error ERROR_TRANSPILING_JOB when trying to simulate the circuit

I'm trying to implement an algorithm (https://dl.acm.org/citation.cfm?id=1128034, basically a simple Grover Algorithm in which the oracle is made of a Fitness operator- some CNOT gates- and 2 adders) ...
3
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0answers
43 views

Simulating depth-2 circuits

Quantum depth-2 circuits can be efficiently simulated classically, as shown in Proposition 2 of this paper. The following is a quote of the proof. After the first time step the quantum state of the ...
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1answer
106 views

Reversible Circuit Simulation (for classical tests of quantum subroutines)

Problem: trying to implement and test quantum subroutines on quantum simulators I run into multiple challenges: Quantum simulation is a very hard problem: a very low number of simulated qubits is ...
2
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1answer
60 views

Implementing noise model in Quantum simulator

I have noticed that a few papers, such as this one, provide models two for typical noise that a qubit encounters during network transmission: Λ is the dephasing channel Λ(ρ) = Pq(ρ) = qρ + (1 − q)ZρZ ...
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2answers
2k views

Why doesn't the Gottesman-Knill theorem render quantum computing almost useless?

The Gottesman-Knill theore states (from Nielsen and Chuang) Suppose a quantum computation is performed which involves only the following elements: state preparations in the computational basis, ...
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3answers
125 views

How to create an Ising coupling gate with Qiskit?

I'm trying to apply a time evolution algorithm for a physical system I'm trying to simulate on QISkit, however, in order to do that, I need to use the so-called Ising coupling gate: $I=\begin{pmatrix}...
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0answers
48 views

Anti-symmetrization on the lattice

Assume, I'm using a system of qubits to simulate a fermionic system. If I'm using the second-quantized formalism (e.g. orbitals in quantum chemistry), the anti-symmetric nature of the fermionic wave ...
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2answers
130 views

How to get samples in “bins” from D-Wave's dimod?

at 1, the following code example is available: ...
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2answers
58 views

GridQubit in Cirq vs LineQubit

It's perhaps a very silly question, but in what ways is it advantageous to use GridQubit vs LineQubits to develop quantum circuits? Specially to develop ansatz ? Are GridQubits Cirq's way of ...
4
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1answer
124 views

How to implement NM Algorithm for Variational Quantum Eigensolver?

First of all: thanks for reading again. I appreciate the feedback I have gotten from this community the past weeks as I started to feel ready to ask questions about quantum computing topics. I am ...
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0answers
25 views

Quantum Codes and Plasma Codes for Simulation Applications

I am wondering if anyone in here has heard/read is involved in quantum codes applied to simulate plasmas? I have read that PPNL is working on that but have not actually seen/found any of their ...
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0answers
48 views

Illustrating limitations of quantum computing

Can you illustrate why even with a functioning quantum computing energy minimization in an Ising Model simulation, an NP-hard problem, cannot be solved?
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1answer
176 views

Plotting Bloch sphere in QuTiP

Is there anyone who reproduced the Bloch sphere given in the paper QuTiP: An open-source Python framework for the dynamics of open quantum systems by J. R. Johansson, P. D. Nation, Franco Nori? I am ...
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0answers
45 views

How to determine the minimum number of experiments needed to compute m-many k-local Pauli expectations?

Say I have an algorithm over N qubits and I want to find the expectation value of an operator $O$ composed of a sum of mterms, each of which is the tensor product of some number of single-qubit Pauli ...
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2answers
544 views

Is there any online Bloch sphere simulator?

While writing this answer I realized it would be really helpful if I could show the OP a video or .gif of how qubit states in Bloch spheres transform under certain unitary operations. I googled up a ...
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0answers
67 views

Simulating quantum computers using anyon braiding

I am new to the concept of topological quantum computation (TQC). Recently I have been thinking about simulating a quantum computer on a classical computer. I know that if I use merely the unitary ...
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1answer
48 views

Interpreting results from IBM's processor vs. simulator

I am working with a circuit where I use 4 cables, and perform measurements in all of them. Nevertheless, I am only interested in the results from two cables since the other two are ancillas. When I ...
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2answers
209 views

Why can't a quantum computer strongly simulate itself?

We can strongly simulate a quantum circuit if we can estimate the probability of measuring $|0^n\rangle$, say, at the end to within some fixed relative error. Now, by measurement, a quantum ...
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0answers
58 views

What are reasonable noise/dephasing parameters for QuEST to emulate state-of-the-art quantum computers?

The QuEST code allows for simulation of quantum computers taking dephasing and depolarizing noise into account via one and two qubit dephasing and depolarization. What are realistic parameters for ...
3
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1answer
124 views

For CNOT gate with control qubit set to 1, the measured state of the second qubit unexpectedly depends on the measurement

I have the following circuit in qiskit. It is a simple CNOT operation with the control qubit set to 1, by running the control qubit through an X-gate. However, when I measure the 2nd qubit, I get the ...
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1answer
54 views

Creating .gifs corresponding to Quirk simulations

Craig Gidney's blog has some .gifs which directly link to the corresponding simulation on Quirk. For example: Grover Search Delayed Eraser Is it possible to create these .gifs from within Quirk? Or ...
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3answers
232 views

Why is there a difference between the simulation results and the actual quantum computer results?

I ran the Grover's Algorithm for 3 Qubits on the IBM Q platform (ibmqx4) and the results of the simulation and the actual computer differ a lot. The screenshots of the circuit and the results are ...
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1answer
79 views

ProjectQ - In which part of the controlled gate object are the control bits scored

I've been trying to decompose the ProjectQ objects and I could manage to decompose non-controlled gates and daggered gates. But I noticed that the object of a controlled version of a gate is the ...
5
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1answer
86 views

Where does the Xmon simulator from Googles cirq framework its entropy from?

Measurements create entropy as we all know. But computers themselves are deterministic machines. Most devices use processor heat as a source for random number generation as far as I know - which has ...
4
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1answer
320 views

How can noise on a device be simulated using measured noise parameters?

The real devices used as backends for Qiskit have calibration data that quantifies errors ($T_1$ and $T_2$, gate fidelities, etc). This can be accessed by, for example ...
4
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1answer
82 views

Introspecting quantum circuit execution on Qiskit Aer simulators

Is there any way to get information from intermediate points in the execution of a quantum circuit. This is not possible on real quantum hardware but would be very useful on the Aer simulators for ...
4
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1answer
94 views

Numerical quantum state tomography simulator

On a classical computer, I want to simulate a learning-based quantum state tomography of a qubit. We can formulate it as finding a parametrized unitary evolution that takes the unknown pure state to a ...
2
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2answers
170 views

Are there emulators for quantum networks?

Inspired by the question Are there emulators for quantum computers?, I'm curious to know if it's possible to emulate a quantum network on a classic computer. Additionally, is it possible to emulate a ...
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1answer
62 views
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1answer
145 views

Unitary gate(s) from product of exponent

Often unitary gates are defined as a product of exponentials, with some parameter in the power-term. However, often it is not clear how to construct unitary gates from it, at least not for me that is. ...
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0answers
398 views

FPGA qubit simulation

This question is regarding the simulation of qubits, using FPGAs. My question is: how does using FPGAs to simulate qubits help us understand or give us an insight into how quantum computers could be ...
2
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1answer
90 views

List of known circuits and their expected output

I've written an API which takes in a circuit scaffold, according to some specifications, and outputs the results of simulating the circuit. The circuit constraints are that the measurements are ...
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0answers
71 views

Deutsch Algorithm on a Quantum Turing Machine

I understood how a Quantum Turing Machine works from this lecture. It would be great if someone could give an example of how this machine could be used to solve a real problem though, for example, ...
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5answers
2k views

How would I implement the quantum oracle in Deutsch's algorithm?

I am trying to simulate Deutsch's algorithm (elementary case of Deutsch-Josza algorithm), and I am not entirely sure how I would go about implementing the quantum oracle necessary for the algorithm to ...
3
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1answer
67 views

Could we use varying voltage with programmable gates?

One of the benefits I'm reading about qubits is that they can be in an infinite number of states. I'm aware of Holevo's bound (even though I don't fully understand it). However, it made me think of ...
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1answer
103 views

How to simulate quantum entanglement variation in different quantum gates?

I'm trying to study quantum entanglement variation during quantum computation with 4 qubit systems comprising a variety of quantum gates. How can I simulate this variation on MATLAB? Is there any ...
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1answer
120 views

Which QC platform is better to use on HPC cluster?

I have a HPC (High Performance Computing) cluster with NVIDIA GPU and Xeon CPU partitions. Is this simulator list complete? Which do you recommended to use on a HPC cluster? Will it increase the ...
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2answers
118 views

How does one obtain amplitude information in Q#?

Is it possible to obtain amplitude information (in lexicographic ordering) for a particular qubit register in Q#? For example, in the following code: ...
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2answers
2k views

Classical Memory enough to store states up to 40 qubits quantum system?

As a part of a discussion with my 'classical' friend, he insisted that making a a state machine for calculating the outcome of quantum computer is possible; so, simply calculate the outcomes of (known)...
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2answers
233 views

Finding the maximum number of Q# simulatable qubits

I'm new to Q# and I was curious on how one would find the number of Q# simulatable qubits for a specific machine. I know Microsoft has an approximation of 16GB ~ 30 qubits but I wanted a better ...