Questions tagged [qiskit]

Qiskit is an open source SDK for working with quantum computers at the level of pulses, circuits and application modules. If appropriate, also use the [programming] tag. Please include the version of Qiskit you use when using this tag.

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Big Endian vs. Little Endian in Qiskit

I've noticed that Q# favors Little Endian. Meaning that most operations are designed for this type of encoding. Is is it the same with Qiskit?
Sorin Bolos's user avatar
12 votes
1 answer
8k views

Evaluating expectation values of operators in Qiskit

I'm wondering how in Qiskit one can calculate the expectation value of an operator given as a WeightedPauli (or, at least, of a single ...
mavzolej's user avatar
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8 votes
3 answers
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Can I find the axis of rotation for any single-qubit gate?

Suppose I have an arbitrary qiskit $U_3$ gate: $U_3(\theta,\phi,\lambda)$. Is there a way I can find which axis the gate is rotating around? In other words, given any real numbers $\theta,\phi,\lambda$...
ZR-'s user avatar
  • 2,388
29 votes
4 answers
12k views

How can I implement an n-bit Toffoli gate?

I want to create a Toffoli gate controlled by n qubits, and implement it in QISKit. Can this be done? If so, how?
Ali Javadi's user avatar
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18 votes
1 answer
13k views

How to measure in another basis

I am new to qiskit and I have to simulate a quantum circuit. I read this documentation https://qiskit.org/textbook/ch-states/single-qubit-gates.html where it is left as an exercise to the reader to ...
thedumbkid's user avatar
15 votes
4 answers
2k views

How is the Grover-Algorithm applied to a database?

Question I want to use the Grover-Algorithm to search an unsorted database for an element $x$. Now the question arises, how do I initialize index and value of the database with the qubits? Example ...
alex's user avatar
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11 votes
1 answer
2k views

What is the relationship between Choi and Chi matrix in Qiskit?

I'm struggling with the framework for quantum process tomography on Qiskit. The final step of such a framework is running fit method of ...
Daniele Cuomo's user avatar
22 votes
1 answer
10k views

What is a "barrier" in Qiskit circuits?

I just started studying IBM Qiskit, and cannot find details about the barrier method on the QuantumCircuit class. It is shown in the circuit drawing, but I never heard about it after reading quantum ...
czwang's user avatar
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31 votes
6 answers
13k views

How do I build a gate from a matrix on Qiskit?

I'm creating a gate for a project and need to test if it has the same results as the original circuit in a simulator, how do I build this gate on Qiskit? It's a 3 qubit gate, 8x8 matrix: $$ \frac{1}{...
Nillmer's user avatar
  • 735
9 votes
2 answers
2k views

Transpilation into custom gate set in qiskit

In qiskit, I can transpile a given circuit into a some predefined gate set as follows (just an example) ...
Nikita Nemkov's user avatar
8 votes
1 answer
8k views

How to create an arbitrary state in QISKit for a local_qasm_simulator?

I would like to play with a quantum circuit local_qasm_simulator in QISKit, but I do not want to implement a separate quantum circuit that would prepare an initial ...
Alexander Pozdneev's user avatar
5 votes
2 answers
2k views

Given a state $|\phi\rangle=\frac{1}{\sqrt{2}}(|0\rangle+e^{i\theta}|1\rangle)$, how do I know the angle $\theta$?

Question1. If there is a state $|\phi\rangle=\frac{1}{\sqrt{2}}(|0\rangle+e^{i\theta}|1\rangle)$, and I want to know the angle $\theta$. What kind of measurement should I do? Could somebody give me ...
WilliamYang's user avatar
4 votes
2 answers
609 views

In Grover's Algorithm, does the exact solution need to be given to the oracle?

From my understanding, the oracle function in Grover's algorithm is used as a way to check for the desired outcome. I have looked at this example which implements the Exactly-1 3-SAT problem and the ...
desirooo's user avatar
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2 votes
2 answers
340 views

quantum random number generator implementation in quantum lab

How can I generate and print a 32 bit sequence of 0s and 1s in Qiskit or IBM Q experience quantum lab using quantum random number generator implementation?
parth's user avatar
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12 votes
4 answers
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How to quickly calculate the custom U3 gate parameters $\theta, \phi$ and $\lambda$ for any unitary?

In IBM Qiskit and Quantum Experience, the custom U3 gate is defined as $$ U(\theta, \phi, \lambda) = \begin{pmatrix} \cos\left(\frac{\theta}{2}\right) & -e^{...
Sanchayan Dutta's user avatar
9 votes
1 answer
3k views

Phase-Shift Gate in Qiskit

How to implement the phase shift gate in qiskit or ibmq? Phase Shift Gate : $$\begin{pmatrix}e^{ia} && 0 \\ 0 && e^{ia}\end{pmatrix} = e^{ia}I$$
Debarghya Kundu's user avatar
8 votes
2 answers
2k views

What are theta, phi and lambda in cu1(theta, ctl, tgt) and cu3(theta, phi, lam, ctl, tgt)? What are the rotation matrices being used?

I was reading the documentation for qiskit.QuantumCircuit and came across the functions cu1(theta, ctl, tgt) and ...
Sanchayan Dutta's user avatar
6 votes
5 answers
1k views

How do I get the Unitary matrix of a circuit without using the 'unitary_simulator'?

I am using jupyter notebook and qiskit. I have a simple quantum circuit and I want to know how to get the unitary matrix of the circuit without using 'get_unitary' from the Aer unitary_simulator. i.e.:...
Jared's user avatar
  • 75
6 votes
2 answers
675 views

How can I find a Clifford+T approximation of an arbitrary one qubit gate in Qiskit?

I know the Solovay-Kitaev algorithm can achieve this. Is there an implementation of this or any other algorithm for the same task in Qiskit? Or perhaps some other library that interfaces well with ...
shashvat's user avatar
  • 805
5 votes
1 answer
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How to implement if statement based on measurement results in qiskit?

I tried to implement three qubit bit flip code in qiskit and need to get the result of measurements and then apply recovery quantum operations conditioned on the measurement results. The following is ...
Jacey Li's user avatar
  • 585
0 votes
1 answer
254 views

Building Unitaries in TSP Quantum Phase Estimation Qiskit?

In the paper [https://arxiv.org/pdf/1805.10928.pdf] 2 published by IBM, they use Quantum Phase Estimation to solve the TSP problem. I don't understand the reason why they can decompose the diagonal ...
Nghia Nguyen Huu's user avatar
0 votes
1 answer
361 views

Error while trying to execute the Quantum Circuits in IBMQ

I have been trying to execute the quantum circuit in the backend of the IBM 16 qubit Melbourne machine. I end up getting ...
Monica's user avatar
  • 311
19 votes
1 answer
9k views

What's meant by the depth of a quantum circuit?

I'm using Qiskit to create quantum circuits wherein I've this attribute called depth. The documentation states it is the length of the critical path here. What does ...
Van Peer's user avatar
  • 577
10 votes
1 answer
4k views

Can I remove gates from a QuantumCircuit?

Suppose I want to implement run several circuits one after another, but they are constructed in a similar fashion. I could reinstantiate a QuantumCircuit for each ...
Alexey Uvarov's user avatar
9 votes
1 answer
1k views

How efficient is Qiskit's unitary decomposition?

In Qiskit's extension package we have the UnitaryGate module that you can initialize using a unitary matrix and then add it to your circuit. How efficiently is this ...
Dani007's user avatar
  • 532
8 votes
1 answer
648 views

SWAP gate(s) in the $R(\lambda^{-1})$ step of the HHL circuit for $4\times 4$ systems

Context: On the 5th page of the paper Quantum circuit design for solving linear systems of equations (Cao et al, 2012) there's this circuit: Schematic: A brief schematic of what's actually ...
Sanchayan Dutta's user avatar
7 votes
1 answer
2k 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 ...
James Wootton's user avatar
6 votes
3 answers
7k views

How can I obtain transformation matrix of a quantum circuit in the Qiskit?

I need to draw a quantum circuit in Clifford+T library and obtain automatically its transformation matrix. Is there any feature on Qiskit in this case?
Moein sarvaghad's user avatar
6 votes
1 answer
2k views

What is the difference between Qiskit execute and the IBMQJobManager?

I was researching how to submit multiple pulse schedules/circuits in the same job and came across 2 methods: Executing Experiments with qiskit.execute and ...
MShakeG's user avatar
  • 411
6 votes
1 answer
1k views

How to get subspace of quantum circuit?

How can I get a subspace of a quantum circuit? More precisely, I'm dealing with quantum circuit with data qubits ('q') and ancilla qubits ('anc'), such as $(q_0,q_1,...,q_n,anc_0,..anc_m)$. After some ...
Jin's user avatar
  • 81
6 votes
1 answer
422 views

Does the circuit with qubit-wise CZ gates compute the inner product of two states? If not, is there another circuit that does?

I've been searching for a quantum algorithm to compute the the inner product between two $n$-qubit quantum states, namely $\langle\phi|\psi\rangle$, which is in general a complex number. One can get $|...
cwhsing's user avatar
  • 63
5 votes
1 answer
225 views

Is there a physical definition of barrier operation in qiskit?

As far as I know, we can use barrier method in qiskit to split circuits into two sets to prevent the optimization. However, is there any physical meaning of the barrier? Like a delay operation or ...
peachnuts's user avatar
  • 1,383
5 votes
1 answer
682 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 ...
James Wootton's user avatar
4 votes
1 answer
786 views

API error when trying to access IBM Quantum Computer using IBMQ API Token

I'm trying to write a code so that if the token exists then it loads the account or else it asks the user for the API token. Below is the code for reference: ...
Shadab Hussain's user avatar
4 votes
1 answer
438 views

How the real IBM quantum computers apply arbitrary Rz(θ) gate rotation? [closed]

I want to ask the following questions: (1) The basis gate set of IBM quantum computers is { Id, Rz(θ),√X, X, CNOT, reset}. Somebody said that IBM didn’t really apply Rz(θ) gate on the machine. The ...
劉承瀚's user avatar
4 votes
1 answer
1k views

What is the difference between Qiskit Terra, Aer, Ignis and Aqua?

I am going through the Qiskit tutorials and they have an article on each of the above 4. however, As a beginner, I am not very clear. Could anyone share some insights on these?
Kittu A's user avatar
  • 173
4 votes
1 answer
252 views

How to make a half adder for x number of qubits with min. cost?

How to make a half adder for N inputs and getting the output on another x+1 output. Where x ...
zircon's user avatar
  • 439
4 votes
1 answer
1k views

How to use external .csv data file in quantum support vector machine qiskit python code?

I am new to python programming and Qiskit. I would like to ask can we use sklearn for adding external .csv data file before Qiskit libraries, or without sklearn, we can do or is there any other Qiskit ...
vis555's user avatar
  • 53
4 votes
3 answers
1k views

How to plot custom gate labels in Qiskit?

How can I create a custom gate in qiskit that is plotted using latex formatting (or another type of formatting)? For example the following code generates a circuit diagram ...
user8627's user avatar
4 votes
2 answers
3k views

How to decompose this two-qubit unitary matrix to the standard gate set?

I have read some of the other decomposition questions here however still don't understand how to do it manually. The matrix I wish to decompose is the following for 2 qubits: $M=\frac{1}{\sqrt2}\...
desirooo's user avatar
  • 117
4 votes
1 answer
199 views

Vary parameter between shots

Is it possible to tell Qiskit to execute a parameterized gate where the parameter varies between shots? Let's say, for whatever reason, I'd like to speed up the dephasing of a qubit during a run. I ...
bRost03's user avatar
  • 579
4 votes
1 answer
1k views

How to implement the swap test with the help of qiskit?

It's creating a real confusion for me especially the parameterized circuit which I have to create. Can anybody please solve this for me? I want to create this circuit.
sohamb172's user avatar
  • 345
3 votes
1 answer
617 views

Trying to construct modular exponentiation gate in Qiskit

https://qiskit.org/textbook/ch-algorithms/shor.html in this tutorial I don't understand especially in how they define for the modular exponentiation gate with only swap gate (inside c_amod15 function)....
Taufiq Datau's user avatar
3 votes
2 answers
1k views

Conjugate transpose of a U-gate

I want to be able to create the circuit depicted below, but running the code below results in an empty circuit when viewing the job afterwards. ...
Anders Julton's user avatar
3 votes
3 answers
2k views

Qiskit: Get approximate execution time

The IBMQ web interface shows both queue position and an approximate execution time for every pending job (see image below). Is there a way to retrieve this information via Qiskit? I know that ...
smuecke's user avatar
  • 77
3 votes
2 answers
998 views

Qiskit: count the type of gates on the qubit with the largest number of gates in a multi-qubit circuit

I would like to know the number and type of all the gates on the wire/qubit with the largest operations in a quantum circuit with multiple qubits. Is there any inbuilt functionality, or what is the ...
quantum's user avatar
  • 575
2 votes
1 answer
914 views

Decomposition of an arbitrary gate using given matrix in Qiskit

If I have an arbitrary non-unitary matrix of say $$ U = \begin{pmatrix} 1.5 & 0 & 0 & 0 \\ 0 & 0 & 0 & 1.6 \\ 0 & 0 & 1 & 0 \\ 0 & 1 & 0 & 0 \\ \end{...
Monica's user avatar
  • 311
2 votes
2 answers
632 views

Mitigating the noise in a quantum circuit

I'm using Qiskit and I have a Quantum Circuit (say, circuit) that gives reasonable results when using the simulator, namely ...
Vitality's user avatar
  • 143
2 votes
1 answer
284 views

Creating a Qiskit Circuit sending $|00\rangle$ to $|1,-\rangle$ and $|11\rangle$ to $|0,-\rangle$

I am trying to create a circuit in Qiskit that performs the following transformations: starting in state |00⟩ generates a √(2)/2 * (-|10⟩+|11⟩) state starting in state |11⟩ generates a √(2)/2 * (|00⟩-|...
Hamideh's user avatar
  • 269
2 votes
2 answers
2k views

Qiskit CNOT-gate matrix mixup?

In the qiskit textbook chapter 1.3.1 "The CNOT-Gate" it says that the matrix representation on the right is the own corresponding to the circuit shown above, with q_0 being the control and ...
Alvo's user avatar
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