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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Path to learn Qiskit as a tool for the future

I am an undergraduate in Engineering physics, yet to take classes on Quantum mechanics, but none (if I'm not mistaken) on quantum information and quantum algorithms, and I am curious about the subject ...
Bidon's user avatar
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3 votes
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Why won't Qiskit ccx gate accept registers?

In Qiskit, they have the concept of a Toffoli gate (ccx). However, the following code throws an error: ...
Woody1193's user avatar
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11 votes
1 answer
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Submitting jobs to IBMQ backend via HTTP API Requests

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. ...
James Wootton's user avatar
2 votes
1 answer
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Plotting data in QISKit using plot_histogram

I'm trying to plot a set of data using plot_histogram, but the rendered image looks like this (the larger values are outside the image): How can I set the y-...
Mathist's user avatar
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TypeError: unorderable types: QuantumRegister() >= int()

I've been using qiskit for about a year now, and as of late, I've had issues finding an available backend to run my circuit on. Looking into the matter, I reinstalled qiskit to find that most ...
Anthony Micciche's user avatar
7 votes
1 answer
263 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), ...
Scott Lawrence's user avatar
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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
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1 answer
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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
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2 answers
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Result of a job for a list of circuits on QISKit

Suppose Circuits= [circuit1, circuit2, ..., circuitn] is a list of defined circuits. Then, ...
Mathist's user avatar
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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 ...
Daniel Mahler's user avatar
1 vote
1 answer
295 views

Entanglement in VQE ansatz in Qiskit

The Qiskit documentation on VQE describes two of the ansatz as "rotations with entanglements". The rotation gates are more or less clear, but the documentation doesn't mention what gate is used for ...
Alexey Uvarov's user avatar
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Programming quantum half adder

While computing the carry bit [C=0 XOR (AB)] I am unable to compute that AB in Qiskit. I don't whether Toffoli gate is available in Qiskit. So does anyone know how to perform AB, which is basically ...
pinkdroid's user avatar
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Qiskit - Authorization Required error

When I use Qiskit to do quantum computing, I suffer from a big problem. When running the code,it turns out to be: ...
bo-ruei Chen's user avatar
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1 answer
1k views

Qiskit - expand and/or merge registers

Suppose one of my functions create some ancillary qubits and reset them. Then, another function wants to create a larger number of ancillary qubits. So, I'd like to reuse the first set of qubits and ...
tigerjack's user avatar
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ModuleNotFoundError: No module named qiskit.providers

The following message I got by running the qft.py code Traceback (most recent call last): File "qft.py", line 18, in ...
Holger's user avatar
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Module BasicAer not found

After installing qiskit-terra via git (pip install qiskit), all python programs involving the line ...
Holger's user avatar
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31 votes
6 answers
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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
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Print circuit compiled on hardware?

I would like to see the compiled circuit as executed on a hardware. Nominally, this sequence of commands should return the QASM circuit in the variable ran_qc, but ...
Jan Balewski's user avatar
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2 answers
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How to fix? 'E1101:Instance of 'QuantumCircuit' has no 'h' member' and 'E1101:Instance of 'QuantumCircuit' has no 'cx' member'

I'm using this simple code to test my Qiskit and learn how to use it but it keeps giving this problems, how do I fix it (Using VS Code and Anaconda Python 3.7) ...
Nillmer's user avatar
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qiskit - Is there any way to discard the results of a measurement?

I have a circuit composed by n qubits, plus a single one which is an ancilla. I'm making multiple measurements on the ancilla at different stages of the circuit, ...
tigerjack's user avatar
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Is it possible to expand/merge different circuits?

Suppose I have created a circuit composed of some registers with the usual qc = QuantumCircuit(qr, cr) where qr and ...
tigerjack's user avatar
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How to set up Qconfig.py and where is the file?

How to set up Qconfig.py and where is the file? I mean under which folder? Like /anaconda/lib/python3.6/site-packages/qiskit/.
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Implementing gate with two parameters using Qiskit in Python

I am trying to implement the HHL algorithm (for solving $Ax=b$). I am assuming $A$ to be unitary and Hermitian so that I can find the Hamiltonian simulation for it easily. For any $A$ to be Hermitian ...
MeetR's user avatar
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9 votes
2 answers
839 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 ...
Mathist's user avatar
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How can the state $\lvert0\rangle+M^{-1/2}\sum_{j=1}^M\lvert j\rangle$ be generated?

I was wondering if anybody to help me to generate the following state. It would be preferable if you use only Hadamard, CNOT and T-gates, on $\lceil\log_2(M+1)\rceil$ qubits: $$|\psi\rangle = \frac{1}{...
Aman's user avatar
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3 answers
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How to run algorithms on IBMQ via Qiskit-Aqua?

I am trying to run an optimization problem on IBMQ. Running the same code on QASM simulator works fine. However, changing only the backend name to IBMQX takes long time. I am aware of the queues ...
Akshay Ajagekar's user avatar
2 votes
0 answers
532 views

Qiskit SDK problem [closed]

So I am getting this error when I fire the command on Ipython or Jupyter Notebook ...
pinkdroid's user avatar
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3 votes
0 answers
651 views

Qiskit Python program cannot connect to QE API

I am just getting started with Qiskit and IBM Quantum Experience, so please forgive my newby question. I have a IBM Quantum Experience account and I generated an API token. I used the generated ...
Bruno Rijsman's user avatar
5 votes
1 answer
419 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 ...
Aman's user avatar
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3 votes
1 answer
225 views

How can I resolve the error QISkit Error: The same provider has already been registered!

I am writing a small algorithm to multiply two numbers using IBM's QISkit. The code is below: times_shell.py ...
Sashwat Anagolum's user avatar
3 votes
3 answers
286 views

How can I get the qiskit module

I have successfully installed qiskit. However, when I try to run a simulation I get the error "No module named 'qiskit' ...
Gene Naden's user avatar
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1 answer
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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 ...
Sashwat Anagolum's user avatar
5 votes
2 answers
2k 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 ...
Daniel Vainshtein's user avatar
4 votes
1 answer
253 views

How to deal with -LookupError: backend "ibmqx4" is not found?

I am using Jupyter notebook to write and running my qiskit codes (python 3.6) and every time I encounter the message: LookupError: backend "ibmqx4" is not found, right now the ibmqx4 computer is not ...
Daniel Vainshtein's user avatar
4 votes
1 answer
1k views

How to install qiskit in spyder editor?

I am working in Anaconda using spyder editor. Can anyone tell me how to install qiskit in spyder?
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8 votes
2 answers
759 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 ...
Jake Xuereb's user avatar
4 votes
3 answers
2k views

Comparing run times on IBM Quantum Experience

I have run this program - ...
Trevor Oakley's user avatar
9 votes
3 answers
866 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 ...
CodeSandwich's user avatar
7 votes
1 answer
1k 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.
Theodore Lewitt's user avatar
5 votes
1 answer
345 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, ...
DrHamed's user avatar
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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
5 votes
1 answer
504 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 ...
Bick's user avatar
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8 votes
2 answers
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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
5 votes
2 answers
533 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, ...
Dr.PB's user avatar
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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
599 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 ...
John Lancaster's user avatar
7 votes
1 answer
493 views

One-qubit gate 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{...
Mathist's user avatar
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10 votes
2 answers
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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, ...
Sanchayan Dutta's user avatar
8 votes
2 answers
1k 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: $a_0$ ------------------- $a_1$-------------------- $\vdots$ $...
brzepkowski's user avatar
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11 votes
2 answers
5k 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 ...
asdf's user avatar
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