All Questions
8,728
questions
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Understanding the Hadamard Gate and what is meant by Qubits
I'm trying to understand the Qiskit documentation in order to see if there are differences in notation from my quantum mechanics lecture notes.
The Hadamard Gate transforms $ |0 \rangle$ into $|+ \...
0
votes
0
answers
8
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TensorCircuit error mitigation
Does TensorCircuit provide built-in error mitigation methods? To see the effect of error mitigation I would like to insert noise channels in the circuit (this is given through tc.channels), then use ...
- 31
2
votes
0
answers
14
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Independence in state prepared by independently drawn Haar random gates
Consider independently drawn $2 \times 2$ Haar random unitaries $U_1, U_2, \ldots, U_n$ and
$$V = U_1 \otimes U_2 \otimes \cdots U_n.$$ Consider the state $\sigma$ given by
$$\sigma = V \rho V^{*}, $$
...
- 995
1
vote
3
answers
29
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How to get exact measurement probabilities when having intermediate measurements with Qiskit?
Suppose we have a circuit with two qubits, A and B. Both are initialized to $|0\rangle$. Over qubit A we apply a single rotation gate (e.g. $R_y$) with an angle given by $x_0$, and then we entangle ...
- 11
1
vote
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23
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Block encoding for a sum of Pauli terms
Given a qubit Hamiltonian with polynomially many local Pauli terms, what is the most natural way of constructing its block encoding? I know there are multiple ways of doing so, but I am looking for ...
- 1,658
2
votes
1
answer
47
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Computing a ratio involving Haar random unitaries
Consider an $n$-qubit Haar random unitary $U$.
I am trying to compute the expression
\begin{equation}
\mathbb{E}\left[ \frac{\text{Tr}\left(|0^n\rangle \langle 0^n | ~U\rho U^*\right)}{\text{Tr}\left(\...
- 995
1
vote
1
answer
43
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What is the expectation value for the ground state of $ H = \sum_i Z_i Z_{i+1} + \sum_i X_i $?
What is the expectation value for the ground state of $ H = \sum_i Z_i Z_{i+1} + \sum_i X_i $ ? In Eq. 15b this provides a solution in k space. The minimum would be reached for $E = -4$. But for ...
- 31
3
votes
2
answers
28
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Are there open source implementations of quantum error correction decoders?
To detect and correct for errors in a topological quantum memory (toric code for example) one needs a quantum error correction algorithm also known as decoder.
The minimum weight perfect matching (...
- 167
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votes
0
answers
13
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custom gate transpilation to implement the HHL algorithm for 4x4 matrices
I'm trying to relalize an HHL algorithm for 4x4 matrix A.
Suppose, $A =
\begin{bmatrix}
11 & 5 & -1 & -1\\
5 & 11 & 1 & 1\\
-1 & 1 & 11 & -5\\
-1 & 1 & -5 &...
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votes
0
answers
10
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Plotting an ROC Curve with Qiskit's VQC
I'm trying to compare VQC to another algorithm using the ROC curve. I thought of using sklearn, but I am having problem replicating a decision_function for the VQC. The sklearn.metrics.roc_curves ...
1
vote
0
answers
13
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Simulate dual Lindblad master equations in the Heisenberg picture in QuTiP
In QuTiP, it is possible to solve Lindblad master equations describing the time evolution of an open quantum system $\rho$:
$$
\dot{\rho}(t)=-\frac{i}{\hbar}[H(t), \rho(t)]+\sum_n \frac{1}{2}\left[2 ...
- 167
2
votes
1
answer
53
views
Why is the Qiskit transpiler not resolving the equivalence $I = R_y(-\theta) R_y(\theta)$?
Suppose you are given the following quantum circuit in Qiskit:
...
- 682
1
vote
1
answer
26
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Problem with qiskit only accepting ${\rm tr}(\rho^2)=1.$ while performing state tomography
I am performing state tomography after a computation cycle in order to store information about the state before measurement and use that information to re-initialise the state for the new cycle of ...
1
vote
0
answers
15
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How to calculate the Pauli Noise model of a physical gate operation?
I've seen literature and QuTip implementation of calculating a gate fidelity given the transformed density matrix, and in that case it uses a number of different initial states. My question however, ...
- 97
1
vote
0
answers
50
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pennylane: How to carry out MB rotation without CB rotation?
I'm looking at this
MBQC tutorial
where there's an example that shows that a MB and CB single qubit rotations give the same result.
CB version :
...
- 1,435
-2
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answers
13
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Scratch wire in Qiskit
When I go through the Qiskit, I found the following one.
Here you can see a term called 'scratch'. What is the real use of this?
0
votes
1
answer
21
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Stim: Surface code with manipulated data qubits
In stim, when we want to create surface code, we can simply do that:
...
- 544
1
vote
2
answers
26
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Problem adding two numbers in a quantum computer with Drapper's algorithm
I would like to add numbers. In this simple example a = 1 and b = 1.
The circuit I created looks like this:
We have two registers a and b. Both have a size of 3 qubits. I'm using Big Endian notation, ...
- 37
0
votes
0
answers
23
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Unexpected behavior of qiskit runtime estimator
When using the qiskit-ibm-runtime estimator (accessing the statevector simulator here) to calculate the expectation value of a Paulistring composed of identities and PauliZs I always get an ...
- 105
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0
answers
12
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AerSimulator measurements
When I use the simulator
Aer.get_backend('aer_simulator')
and the circuit contains measurements at the end, how do Qiskit performs these measurements?
I thought ...
- 341
3
votes
0
answers
40
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Quantum entanglement as topological entanglement
According with Aravind:
the Hopf link, L2a1, corresponds to the Bell state $\frac{1}{\sqrt 2}\big (|00\rangle+|11\rangle\big )$,
the Borromean link (L6a4) can be considered as GHZ state $\frac{1}{\...
- 131
0
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0
answers
62
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Conditions for Fault-tolerant QC to work better than not doing any EC (except the ideal decoder)
I've been exploring fault-tolerant QC with the simplest 7-qubit Steane code, yes I'm able to obtain all the predicted thresholds for various transversal gates and the EC gadgets. I then tried to ...
- 13
3
votes
1
answer
62
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Is Qiskit transpile function (with basis_gates=['u', 'cx']) universal?
It's well known that the single-qubit rotation gate $U(\theta, \phi, \lambda)$ and the controlled-not gate $CX_{i,j}$ form one of the universal set of gates for quantum computation. So here's my ...
- 682
2
votes
1
answer
72
views
How many gates can I put on a 27 qubit quantum computer
Recently I've been wondering how many gates I can put on a 27 qubit quantum computer, for example can I put like a million gates?
And also will that increase the time for the result to be calculated?
- 29
0
votes
0
answers
13
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Time ordering in topological cluster state creation
When performing syndrome measurements of the surface code, the time ordering of the CNOT\CZ gates between data and ancilla qubits is important. Namely, not every time ordering is valid.
Is it the same ...
- 45
-3
votes
0
answers
60
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How to compute a divide operation and add it to initialize function [closed]
Let Q={s1,s2...sn} with si = [P1,P2,...Pn,q1,q2...qn]` with this order.
Let $${|\psi_0>} = \frac{1}{\sqrt{n}}\sum_{i=0}^{n} {|q_i>}$$ the initial state of my circuit with Q, which I will ...
3
votes
2
answers
107
views
Converting $T_1$ and $T_2$ decay rates to noise supported by stim
Stim only supports Pauli noises like DEPOLARIZE1, DEPOLARIZE2, X_ERROR, ...
- 55
1
vote
2
answers
55
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How to implement Hamiltonian $0.01Z$?
I have a task in an assignment that wants me to apply a Hamiltonian to a state.
The Hamiltonial is 0.01*sigma_z. I know how to apply a Z gate to a state but I don't know to process the factor 0.01 in ...
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0
answers
19
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why entanglement of an Antiferromagnetism case decreases in presence of a nonuniform magnetic field?
supposing a two qubit xxx Heisenberg chain in presence of a non-uniform external magnetic field (in z direction), the Hamiltonian of the system is as follow:
H = J (σx ⊗ σx + σy ⊗ σy + σz ⊗ σz ) + (B-...
- 89
3
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0
answers
51
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Is it ever beneficial to communicate qubits that aren't EPR pairs?
When Alice wants to send a qubit $q$ to Bob, she doesn't have to send $q$ itself. She can instead generate an EPR pair $(a, b)$, send $b$ to Bob, and teleport $q$ to Bob by consuming $(a,b)$ and ...
- 27.2k
3
votes
1
answer
40
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Are MUBs complex projective 3-designs?
Consider a finite subset $X\subset\mathbb{CP}^{d-1}$ of $d$-dimensional pure states.
Following e.g. (Roy and Scott 2007), we say that $X$ is a complex projective $t$-design if
$$\frac1{|X|}\sum_{x\in ...
glS♦
- 20.7k
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votes
1
answer
14
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How to change the qubits of a cirq Circuit?
I am constructing generic circuits, and I would like to change the qubits after creating the circuits. Is there a way in cirq to do so?
for instance:
...
- 325
3
votes
1
answer
74
views
Which gate based quantum computer is the best? [closed]
I am interested in Drug Discovery and Materials Simulation.
I was told that the IBM 433 qubit quantum computer can only do a circuit of 11 qubits x 11 gates. And Honeywell's quantum computer can only ...
0
votes
0
answers
19
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How to install qiskit-research in IBM quantum lab?
When I study ‘Dynamic decoupling’, one method is add_dynamical_decoupling.
Firstly I should install qiskit_research in my ...
0
votes
1
answer
19
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Basic import problem for qiskit_experiments module, how to fix?
I'm trying to make use of the qiskit_experiments module but I always get a "No module named 'qiskit_experiments'" error while trying to import it. I've uninstalled and reinstalled qiskit in ...
0
votes
0
answers
26
views
Topmost Universal Gate Based Quantum Simulator?
I am Elijah I'm interested in Drug Discovery and Materials Simulation. I want to purchase a gate based Quantum Simulator for research. I received a proposal.
Full State Simulator 30 Qubits on Laptop, ...
1
vote
1
answer
92
views
stim : How to create a circuit like qiskit's c_if
In qikit, there is a circuit called c_if that feeds back to the quantum circuit according to the measured results.
https://qiskit.org/documentation/stable/0.39/stubs/qiskit.circuit.InstructionSet.c_if....
- 21
1
vote
0
answers
20
views
is it possible to use STIM for non-clifford circuits?
I know STIM is for clifford gate circuits but I wonder if there is a way around this? Is it possible to use STIM for non clifford circuits? Do we have any example for it?
- 544
0
votes
1
answer
33
views
Do detection events mean temporal and spatial coordinates?
In pymatching, the check_matrix structure is for stabilizers rather than measurement outcome of stabilizers.
I want to plot "matching" for my measurement outcomes.To do that, I need to ...
- 544
1
vote
1
answer
54
views
Classical register implementation in Amazon Braket
How to implement classical register in a quantum circuit in Amazon Braket ? I am trying to preproduce results of a circuit build in qiskit on AWS braket services. Thanks
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8
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Has anyone had problems installing Q# QDK on VS2022? looks like you need dotnet 4.5 [closed]
I installed VS2022 Community Edition, then installed the Microsoft Quantum Development Kit Extension from the Visual Studio marketplace from within VS. The extension downloaded and the VSIX installer ...
- 1
3
votes
1
answer
67
views
Classes of quantum circuits that can be "efficiently" simulated
Which kind of quantum circuits can be simulated with classical algorithms in a reasonable amount of time (for a large number of qubits)?
For example the ones with only Clifford gates. Or the ones with ...
- 341
0
votes
1
answer
24
views
Why does the single-shot error correction with 3D gauge color codes save qubits or times?
I read about single-shot error correction using 3D gauge color codes. I saw the claim that it enables significant qubit and time overhead improvement regarding 2D surface codes, since it does not ...
- 45
0
votes
1
answer
30
views
How to extract resulting qubit states from a circuit after one round of computation?
I'm running the simulation of some circuit on the Qiskit qasm_simulator backend. My end goal is running this simulation several times and finally extract for each iteration the final qubit state and ...
2
votes
1
answer
48
views
Grover, CCZ Gate on IBM Quantum Lab & unexpected outputs
Studying Grover on IBM lab using Qiskit. But the following code produces unexpected outputs. Note that `PhaseOracle produces 2 CCZ gates. Could anyone check (and explain) why are those unexpected ...
- 23
0
votes
1
answer
14
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Pymatching decoder version in sinter package
Does the "Pymatching" decoder of the "sinter" python package use Pymatching 1.0 or 2.0?
https://pypi.org/project/sinter/
- 45
0
votes
1
answer
32
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Is there a state vector simulator written in pure python?
For educational purposes, I am looking for a simulator written in pure python.
It may use scientific-python libraries such as numpy to exploit the data structures they provide, but the core algorithms ...
1
vote
1
answer
26
views
IBM Quantum Computing Pulse Control
Does any body know if there is a free IBM quantum computer that supports Pulse Control? All of the ones I see don't support it.
3
votes
2
answers
53
views
Why is rz gate error not exactly zero in IBMQ washington device?
I am looking at the calibration data for IBMQ's washington device (which is published daily) and am finding non-zero values for the field "rz_gate_error_value".
I used to think that RZ gates ...
- 157
2
votes
1
answer
45
views
traveling salesman output from qiskit docs
In this tutorial https://qiskit.org/textbook/ch-paper-implementations/tsp.html I understood most of the steps of how to build it, but not the result. In the code, I see they don't get to the part of ...
- 135