Questions tagged [ibm-q-experience]

Use this tag for questions about IBM's Quantum Service - Circuit Composer & Quantum Lab. DO NOT use this for questions about general Qiskit issues (use [qiskit] for that).

Filter by
Sorted by
Tagged with
5 votes
2 answers
974 views

Trying to build a circuit for quantum teleportation on IBMQ I get ERROR_RUNNING_JOB error

I am trying to build a circuit for quantum teleportation. On the simulator, everything runs fine and according to expectations, however, I am not able to run the algorithm on the real quantum ...
user avatar
19 votes
1 answer
6k 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 ...
user avatar
  • 749
5 votes
2 answers
873 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 ...
user avatar
9 votes
3 answers
3k views

How to implement the "Square root of Swap gate" on the IBM Q (composer)?

I would like to simulate a quantum algorithm where one of the steps is "Square root of Swap gate" between 2 qubits. How can I implement this step using the IBM composer?
user avatar
  • 1,098
6 votes
2 answers
417 views

Simple Hadamard Circuit gives incorrect results?

I am running the simplest Hadamard circuit possible - one qubit, initialised to 0, apply H gate, measure in Z basis. When I run the circuit on the simulator I obtain the expected result (50% in 0, 50% ...
user avatar
1 vote
2 answers
169 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?
user avatar
  • 245
9 votes
1 answer
2k views

Phase-Shift Gate in Qiskit

How to implement the phase shift gate in qiskit or ibmq? Phase Shift Gate : $$\begin{pmatrix}e^{ia} && 0 \\ 0 && e^{ia}\end{pmatrix} = e^{ia}I$$
user avatar
7 votes
1 answer
875 views

Physical implementation of gates on IBM Q

There is a lot of quantum gates in IBM Q Composer, however, only few are implemented physically while others can be composed of them. When one looks at description of a quantum processor in IBM Q ...
user avatar
0 votes
1 answer
169 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 ...
user avatar
  • 151
3 votes
1 answer
58 views

What is the best IBMQ provider to South America?

What is the best option for South America Brazil to configure: provider.get_backend (''), because melbourne_16 is very slow.
user avatar
4 votes
1 answer
824 views

Simpler implementation of the Toffoli gate on IBM Q for special circumstances

On current quantum hardware, a depth of circuit is constrained because of noise. In some cases, results are totally decoherent and as a result meaningless. This is especially true when Toffoli gates ...
user avatar
3 votes
2 answers
1k views

How do the credit points work in IBM quantum experience?

I am using Qiskit language, and I am working with IBM devices via Quantum Experience beta. How can I find how many credit points I have used and how much there are left till they fill back 24 hour's ...
user avatar
2 votes
1 answer
357 views

IBM Slack links broken

Does anyone know where I can find working Slack invite links to any of IBM's Slack pages? The Slack links on this support page are all broken. Thank you.
user avatar
2 votes
2 answers
424 views

Why IBM Quantum Experience is giving different results under ibmq_qasm_simulator and ibmq_16_melbourne?

I am trying to run following 6 qubit quantum circuit and I am getting different results under ibmq_qasm_simulator and ibmq_16_melbourne (both involving 8192 shots). What is the reason? ...
user avatar
11 votes
3 answers
2k views

Implementation of the oracle of Grover's algorithm on IBM Q using three qubits

I am trying to get used to IBM Q by implementing three qubits Grover's algorithm but having difficulty to implement the oracle. Could you show how to do that or suggest some good resources to get ...
user avatar
  • 842
6 votes
2 answers
1k views

What is maximum circuit depth and size IBM Q5 and Q16 could handle?

I'm trying to implement a couple of algorithms on ibmq_16_melbourne, so I need to know if this device is able to handle with depth and size of my current circuit or ...
user avatar
  • 728
3 votes
2 answers
250 views

IBM Quantum Experience API Without QISKit

I am a computer science master's student who is doing research in the field of quantum computing. I have an IBM quantum experience account(https://quantum-computing.ibm.com/) and as such I was ...
user avatar
  • 31
8 votes
1 answer
689 views

Depolarizing channel implementation on IBM Q

Given a single qubit in the computational basis, $|\psi\rangle =\alpha |0\rangle + \beta|1\rangle$, the density matrix is $\rho=|\psi\rangle\langle\psi|=\begin{pmatrix} \alpha^2 & \alpha \beta^*\\ ...
user avatar
  • 485
6 votes
1 answer
359 views

Why is a different convention used for the $Rz$ implementation on IBM Q?

A $z$ rotation gate is defined as $$ Rz(\theta)=\mathrm{e}^{-i\frac{\theta}{2}Z}= \begin{pmatrix} \mathrm{e}^{-i\frac{\theta}{2}} & 0 \\ 0 & \mathrm{e}^{i\frac{\theta}{2}} \end{pmatrix}, $$ ...
user avatar
4 votes
1 answer
121 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 ...
user avatar
  • 549
4 votes
1 answer
329 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: ...
user avatar
2 votes
2 answers
408 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 ...
user avatar
  • 143
1 vote
1 answer
133 views

How to get QASM code from IBMQ experience

I am interested in retrieving the OpenQasm code of a quantum circuit, as it appears on IBM Quantum Experience. This is the code that the quantum machine actually runs. I used to be able to just copy ...
user avatar
  • 102
6 votes
1 answer
748 views

What is the state of the art on Quantum Random Access Memories? [duplicate]

I realized that Quantum Random Access Memory (qRAM) was proposed to make quantum computers more similar to classical one. Currently quantum computers have very constrained memory, given only quantum ...
user avatar
3 votes
1 answer
404 views

Cannot replicate results in article on pricing financial derivatives on IBM Q

I am trying to implement a circuit for searching for the largest eigenvalue and respective eigenvector of an operator, i.e. phase estimation, introduced in article Towards Pricing Financial ...
user avatar
3 votes
1 answer
143 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 ...
user avatar
  • 381
17 votes
1 answer
3k views

Which subatomic particle does each company use in quantum computing?

Probably each company (Google, Amazon, Intel, IBM, Microsoft, D-Wave and so on) uses a mix of subatomic particles and technologies. I would like to know which particles/technologies are used by each ...
user avatar
9 votes
3 answers
4k 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^{...
user avatar
2 votes
1 answer
231 views

When increase the shot, why the result is different?

when I measure the shot = 1024 when I measure the shot = 8192 I want to derive result value 011(=3) However, I know if measure the more shots, increase the accuracy. why this result derive??? why ...
user avatar
  • 189
15 votes
2 answers
7k views

How to implement the 4 Bell states on the IBM Q (composer)?

I would like to simulate the 4 "Bell States" on the IBM composer? How can I best implement those 4 Bell states using the existing set of gates ? Here below you see the definition of the 4 Bell ...
user avatar
  • 1,098
8 votes
3 answers
2k views

Access results from an experiment without having to run the script again

I have ran an experiment in one of the IBM processors and the work has finished. However, I can not obtain the data as histograms or counts in the qiskit notebook because the experiment was concluded ...
user avatar
  • 113
4 votes
1 answer
219 views

Do all physical architectures for quantum computers use the same universal gate sets?

Now I have understood that physical implementation of quantum computer need a universal quantum gate set like Clifford+T to realize any unitary quantum gate. However, I don't know if it is all the ...
user avatar
4 votes
2 answers
842 views

Question About How Qiskit Reset Gate Affects Other Entangled Qubits

I am trying to understand how the reset gate in Qiskit affects qubits its entangled with. Consider the following circuit with qubits $q_0$ and $q_1$: Where circuit240 takes $|0\rangle$ to $a|0\rangle ...
user avatar
3 votes
1 answer
676 views

What is the $\lambda$ parameter in the $U3$ gate used for?

The most general single qubit gate is $\mathrm{U3}$ given by matrix $$ \mathrm{U3}= \begin{pmatrix} \cos(\theta/2) & -\mathrm{e}^{i\lambda}\sin(\theta/2) \\ \mathrm{e}^{i\phi}\sin(\theta/2) & ...
user avatar
12 votes
1 answer
3k 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 ...
user avatar
  • 385
4 votes
3 answers
2k views

Comparing run times on IBM Quantum Experience

I have run this program - ...
user avatar
2 votes
1 answer
302 views

$T_1/T_2$ thermal relaxation example

The built in noise models in Qiskit have an example of $T_1/2T_2$ relaxation here. I have a couple of doubts; the notebook is not very clear in some of the steps. Why does one need $T_2\leq 2T_1$? ...
user avatar
11 votes
1 answer
467 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. ...
user avatar
11 votes
1 answer
3k views

How can a controlled-Ry be made from CNOTs and rotations?

I want to be able to applied controlled versions of the $R_y$ gate (rotation around the Y axis) for real devices on the IBM Q Experience. Can this be done? If so, how?
user avatar
9 votes
2 answers
2k 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, ...
user avatar
8 votes
2 answers
532 views

Practical Implementations of QECCs in IBM Q Experience

I am learning how to program the IBM Q Experience quantum computers in order to learn more about how does it work and in order to perform some experiments in it. By doing so I was wondering what are ...
user avatar
7 votes
1 answer
940 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.
user avatar
6 votes
2 answers
577 views

Custom gates on IBM Q

I realized that QASM supports custom gates. However, when I tried to create the gate, transpiling error appeared both on simulator and real quantum processor. I suspect that IBM has not implemented ...
user avatar
5 votes
2 answers
309 views

How to implement the CCH gate in quantum computers available in clouds?

How to implement CCH gate in quantum computers available in clouds? If there is not any gate directly available for it, what are the possible ways to represent CCH?
user avatar
5 votes
1 answer
162 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 ...
user avatar
  • 1,223
5 votes
1 answer
2k views

How to make circuit for n-control Z gate( i.e $C^3Z$ )?

I am trying to make circuit for $C^3Z$ gate I have seen a circuit for $C^2Z$ or $CCZ$ gate made by using $CCX$ gate so is there any way to make circuit for $C^3Z$ in this similar manner( i.e by using $...
user avatar
  • 381
4 votes
1 answer
738 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 ...
user avatar
  • 341
3 votes
2 answers
144 views

Why IBM devices have the same number of qubit and the same architecture, but the error rates are different?

Here are two different IBM quantum online devices, Both of them have the 5 qubits and the same architectures. But why do they have different error rate? What's the different between them?
user avatar
  • 1,223
3 votes
0 answers
128 views

Difficulty in implementing Grover's Algorithm with large number of qubits

It seems IBM offers a 15 qubit quantum computer through their quantum experience program. However, upon a quick search through the literature, the largest implementation of Grover's algorithm I have ...
user avatar
  • 31
3 votes
2 answers
708 views

Explanation of output produced by the following quantum circuit

I've recently started reading about quantum computing and I apologize in advance if this is (and I think it probably is) a very simple question. I've created the following circuit. I believe I ...
user avatar
  • 133