Questions tagged [qiskit]
Quantum Software Development Kit for writing quantum computing experiments, programs, and applications. If appropriate, also use the [programming] tag.
212
questions
16
votes
3answers
3k 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?
12
votes
3answers
714 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
...
10
votes
2answers
342 views
Composing multiple quantum circuits in single quantum program in QISKit
I was wondering if there is a way to compose a program with multiple quantum circuits without having the register reinitialized at $0$ for each circuit.
Specifically, I would like run a second ...
9
votes
3answers
354 views
Does conditional gate collapse controller's superposition?
I've created a simple circuit in Q-Kit to understand conditional gates and outputted states on each step:
In the beginning there is clear 00 state, which is the input
The first qubit is passed ...
9
votes
2answers
802 views
Quantum algorithm for linear systems of equations (HHL09): Step 2 - Preparation of the initial states $|\Psi_0\rangle$ and $|b\rangle$
This is a continuation of Quantum algorithm for linear systems of equations (HHL09): Step 2 - What is $|\Psi_0\rangle$?
In the paper: Quantum algorithm for linear systems of equations (Harrow, ...
8
votes
2answers
227 views
How to program a controlled Hadamard-Hadamard gate?
I'm trying to program a controlled gate as the figure below in Qiskit. Should it be sufficient to separate and control individually the Hadamard gates?
8
votes
2answers
421 views
Qubits specification on IBMQ devices
As it is shown here, CNOT gates between different qubits have different error rates. I have the following questions:
1) While defining a circuit on QISkit, does ...
8
votes
2answers
439 views
There was an error in the circuit!. Error = 'QISkit Time Out'
I've got the following quantum code using QISKit (based on hello_quantum.py):
...
8
votes
1answer
554 views
How to delete pending jobs on IBM Quantum Computer to retrieve units?
I am trying to run some code using qiskit, but I get the error message, that I have run out of necessary Experiment Units. I ...
8
votes
1answer
240 views
Submitting jobs to IBM devices without Python
Qiskit can be used to submit jobs to IBM devices using Python (or Swift and JavaScript). But what if I want to use a different language?
For example, suppose I have a specific circuit I want to run. ...
8
votes
1answer
2k views
Visualization of Quantum Circuits when using IBM QISKit
I have followed the installation steps, regarding QISKit working environment. For circuit visualization, I've installed latex as in addition to poppler to convert from PDF to images. Afterwards, I ...
7
votes
1answer
719 views
Phase-Shift Gate in Qiskit
How to implement the phase shift gate in qiskit or ibmq?
Phase Shift Gate : $$\begin{pmatrix}e^{ia} && 0 \\ 0 && e^{ia}\end{pmatrix} = e^{ia}I$$
7
votes
1answer
386 views
Changing indices of qubits in QISKit
I was wondering if something like this is possible in QISKit: let's say we have two registers containing target and ancilla qubits:
$a_0$ -------------------
$a_1$--------------------
$\vdots$
$...
7
votes
1answer
273 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 ...
7
votes
1answer
292 views
One-qubit gates results in QISKit
I found it odd that the result of the action of identity gate (namely a $2\times2$ identity matrix) on a pure state $|0\rangle$ (namely the vector corresponding to the $2\times1$ matrix $\begin{...
6
votes
1answer
784 views
What are theta, phi and lambda in cu1(theta, ctl, tgt) and cu3(theta, phi, lam, ctl, tgt)? What are the rotation matrices being used?
I was reading the documentation for qiskit.QuantumCircuit and came across the functions cu1(theta, ctl, tgt) and ...
6
votes
1answer
277 views
Defining qubit operator from scratch
I'm a beginner with Qiskit and the Python language at all.
Here is my question:
One of the VQE function arguments is qubit operator (qubitOp).
I saw some examples ...
6
votes
2answers
301 views
Why do we need a Classical Register for carrying out Quantum Computations?
I've just started to mess about with QISKit on Python and one thing is confusing me a fair bit.
Given that we are building Quantum Circuits what is the need for a classical register ?
Is it because ...
6
votes
2answers
155 views
Construct Controlled-$G^{\dagger}$ from known Controlled-$G$
Let there be a known a scheme (quantum circuit) of Controlled-G, where unitary gate G has G$^†$ such that G≠G$^†$ and GG$^†$=I (for example S and S$^†$, T and T$^†$, V and V$^†$, but not Pauli and H ...
6
votes
1answer
630 views
How would one implement a quantum equivalent of a while loop in IBM QISkit?
I'm writing a simple multiplication algorithm that uses the Quantum Fourier Transform to repetitively add a number (the multiplicand) to itself and decrements another number (the multiplier). The ...
6
votes
1answer
110 views
Why does job.running in QISKit output False, even if the job is still running?
I submitted a job in the 0.5.0 version of QISKit using
job = execute(qc, 'ibmqx5', shots=shots)
This just submits the job, and does not wait for a result.
I ...
6
votes
1answer
172 views
How does measurement calibration work?
One of the possible ways to improve the results of an experiment on the IBM machine using the Qiskit language is to use the measurement calibration methods. This is the link to the documentation.
I ...
5
votes
5answers
1k 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:
$$
\frac{1}{...
5
votes
3answers
457 views
What does fidelity mean?
I am learning qiskit software and this term keeps popping up and I am unable to get a grasp on the technical definition given by wikipedia. For example, the functions state fidelity and process ...
5
votes
2answers
204 views
Transform matrix into a combination of simple quantum gates
I am trying to transform this matrix into a combination of quantum gates but I cannot find any such functionality on Qiskit or anywhere else. I have tried to use Quirk but I do not understand it.
$$\...
5
votes
1answer
232 views
What is the purpose of the TDG gate in QISKit?
The QISKIT documentation doesn't explain what a TDG gate does and I can't find it anywhere else online.
5
votes
1answer
756 views
What is Qconfig in QISKit and how do I set it up?
To use certain things in QISKIt, such as acessing the real quantum processors, it seems that there is a file 'Qconfig.py'. That needs to be set up.
How do I do this?
5
votes
1answer
165 views
Status of software packages for quantum compiling
By "quantum compiling", what I mean is classical algorithms to solve the following problem: given a $SU(D)$ matrix $U$ (the goal) and a set of $SU(D)$ unitary matrices $V_1 \cdots V_N$ (the gates), ...
5
votes
1answer
231 views
How to calculate the fidelity of a certain gate of a IBMQ device in Qiskit using randomized benchmarking/tomography?
For example, I want to calculate the fidelity of a 1-qubit and 2-qubit gates (similar to the result shown in figure 2 in this paper). Is there any way to do that in Qiskit? I've gone through the ...
5
votes
1answer
250 views
Quantum SVM Algorithm Error on import
I am experimenting with some Qiskit ACQUA AI algorithms which require the following import statement:
from datasets import *
However, ...
5
votes
2answers
274 views
Checking value of variable using quantum approach
A beginner question after watching few videos.
Say, var=a; var can be either of two values, ...
5
votes
1answer
174 views
Get result measurement into a circuit with Qiskit
I'm trying to implement the three qubit bit flip code in Qiskit.
Therefore, I need to get the result of a measure of two ancilla qubits, to deduce which gate I need to use do recover my logical qubit....
5
votes
1answer
325 views
Quantum algorithm for linear system of equations (HHL) - Final Step: How can I find my vector of solution $|x\rangle$?
I'm working on solving a linear system with the quantum algorithm HHL. I don't understand how I can recover my vector $|x\rangle$ of real solution of the system starting from the states measured with ...
5
votes
1answer
197 views
Entanglement state preparation by using amplitude values
I have an algorithm that uses QRAM, after accessing the given QRAM that store M d-dimensional classical vectors, the state of the index register and the data register become entangled. But for now I ...
5
votes
1answer
279 views
Is there a common set of modules for user-defining-quantum-gate for QISKit
I am wondering if there exists a common library or a set of modules for user-defining-quantum-gate for QISKit.
If it does, could you tell me?
By referring to Define Quantum Gates and How to define ...
5
votes
0answers
70 views
Graphing the decoherence of qubits being used to perform an algorithm
How would I be able to graph the decoherence of qubits being used to perform an algorithm? I'm working with the IBMQ Qiskit framework and I'm trying to write a program that allows me to find the ...
4
votes
3answers
484 views
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^{...
4
votes
1answer
953 views
ImportError: cannot import name 'QuantumProgram' from 'qiskit'
I get below error when I run a code on spyder environment:
File C:/MYPYTHON Programs/My Quantum Programs/Shor algo.py, line 4, in from ...
4
votes
1answer
275 views
About the Qiskit draw function
Where does Qiskit put the rendered figure created by circuit.draw(output='mpl')?
4
votes
1answer
1k 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 ...
4
votes
1answer
104 views
How to parallelly run a quantum circuit on IBMQ?
I am trying to implement the following circuit
and my code is
The above circuit has size 5 and depth 3. My question is, how can I run the circuit parallelly. I mean, the gate ...
4
votes
3answers
109 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:
$I=\begin{pmatrix}...
4
votes
1answer
264 views
Can I remove gates from a QuantumCircuit?
Suppose I want to implement run several circuits one after another, but they are constructed in a similar fashion. I could reinstantiate a QuantumCircuit for each ...
4
votes
1answer
292 views
How can noise on a device be simulated using measured noise parameters?
The real devices used as backends for Qiskit have calibration data that quantifies errors ($T_1$ and $T_2$, gate fidelities, etc). This can be accessed by, for example
...
4
votes
2answers
430 views
How to create a condition on only one classical bit when we have a total of 2 classic bits in the system
I am trying to make a quantum circuit with one qubit and 2 classical bits for each measurment in the system below:
I want to make condition on the first bit: if the first collapse to zero so x ...
4
votes
1answer
60 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 ...
4
votes
1answer
66 views
Resources in Spanish to start learning quantum computing and quantum programming (Qiskit)
I’m starting an engineering degree in computer systems and I’m starting to get really interested in quantum computing. First of all, I don’t know where or how to start and I would really like to learn ...
4
votes
1answer
223 views
Controlled unitary from the HHL algorithm – practical implementation using Qiskit
I have a question about the implementation of the controlled unitary $e^{iAt}$, from the paper Demonstration of a Quantum Circuit Design Methodology for Multiple Regression, using the Qiskit framework....
4
votes
1answer
363 views
Qiskit - How do we measure the same single qubit system multiple times while also getting the counts/results after each measurement?
I am able to apply multiple measurements (2) to the same qubit system. However, I would like to get the counts right after each measurement is executed. I realize that the counts should be the same ...
4
votes
1answer
367 views
Deprecation warnings in Qiskit (circuit drawing)
I am just starting to get around Qiskit, I'm going at baby steps, so I tried to run the code below and I noticed three things:
I tried using ...
