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Questions tagged [ibm-q-experience]

Use this tag for questions about IBM's quantum processors which are accessible online. DO NOT use this for questions about general Qiskit issues. As of July 2018, there are five processors on the IBM Q Experience: two 5-qubit processors, one 16-qubit processor and two 20-qubit processors (only available to hubs, partners, and members of the IBM Q network).

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Experiments stuck on VALIDATING ibmq_16_melbourne

Since yesterday I'm trying to run on the new composer (quantum-computing.ibm.com) both new experiments (never run before) and older experiments (that have been successfully run and completed some ago) ...
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1answer
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Back End for Reset Gate

IBM's simulator allows the use of a reset gate ($|0\rangle$ gate) however when I try to run a circuit using this gate on the hardware it fails to execute. Is there a plan to physically realize this ...
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1answer
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Weeding out qubit states with leftmost qubit as 1

Need help! I was working on a project when I required to use a projection operator. For an example case, I have the Bell state, $$|\psi\rangle = \frac1{\sqrt2}\left(\color{blue}{|0}0\rangle+|11\rangle\...
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1answer
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Visualizer error in IBM Q Experience Beta

I am noticing some erroneous behavior coming from the visualizer in some circuits I was running. I am not sure how widespread the issue is, but see the attached image for some strange behavior with ...
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Results from looped experiments on IBM Q different than individual experiments

I'm experiencing an issue while using Qiskit where the counts from a job return vastly different values when ran in a loop or as an array of circuits as opposed to single experiments when run by ...
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1answer
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How to implement the XY Heisenberg interaction using IBMQ and Qiskit?

A possible way to implement the 2 qubit Heisenberg XYZ model using a Quantum computer is to decompose the Hamiltonian as follows: $$H_{XYZ} = H_{XY} + H_{YZ} + H_{XZ}$$. In this case, these operators ...
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1answer
72 views

2-qubit QFT in IBMQ: controlled phase rotation

I've started getting into quantum computing in the last few days. As part of the learning, I've figured it would be fun to implement some circuits on IBMQ Experience as I learn. So now I'm stuck with ...
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IBM Q devices scheduling of gates with different durations

I was trying to figure out how scheduling works in IBM devices. The thing that's bugging me is that in the quantum computer implementations I had seen before, the cycle concept is used. Say, for ...
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1answer
43 views

How to define custom controlled unitaries in OPENQASM 2.0?

According to the OPENQASM 2.0 documentation, it's possible to define custom unitary gates using the format: gate name(params) qargs { body } where the optional ...
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1answer
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Implementing Deutsch's problem on IBM Q composer

I tried to implement the Deutsch's problem on IBM Q but didn't get the results as expected. So here is the circuit for the Deutsch algorithm and this is my implementation on the composer: so let me ...
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How to run quantum SVM algorithm from Qiskit in real IBM Quantum Computer using IBMQ?

I'm trying to run QSVM algorithm in IBMQ experience, want to run in one of those real quantum computers. ...
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IBM Q devices' hardware/resource constraints

I tried to look for the resource constraints but so far haven't been able to find them. They are not present in the GitHub repository that usually provides the hardware information for the different ...
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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^{...
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2answers
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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 ...
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IBM QISKit: creating a variational algorithm from zero

I would like to implement a variational algorithm (similar to VQE but with another cost function, no expectation of a Hamiltonian involved) from zero. Is there any tutorial explaining how to implement ...
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1answer
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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 ...
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How to measure a Bell inequality violation in IBM Q?

Note: Cross-posted on Physics SE. I made some circuit to prepare a 2 qubit state, but I am having trouble understanding how to measure Bell's inequality. I know the inequality is of the form $$|E(a,...
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1answer
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Interpreting results from IBM's processor vs. simulator

I am working with a circuit where I use 4 cables, and perform measurements in all of them. Nevertheless, I am only interested in the results from two cables since the other two are ancillas. When I ...
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What interesting properties can I measure with a 1 qubit state?

I am playing with the IBM Q and I would like to know what interesting properties I can measure with only a 1 qubit state. This is because things like Bell's inequalities, concurrence, PPT criterion, ...
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1answer
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Making a maximally mixed 2-qubit state in the IBM Q

I am trying to make a 2-qubit maximally mixed state $\mathbb{I}/4$ where $\mathbb{I}$ is the identity $4\times 4$ matrix. I know that, for a maximally mixed 1-qubit state I can use a Hadamard gate, ...
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Implementing a depolarizing channel for 2 qubits on IBM Q

I am trying to use IBM Q to perform the following depolarizing channel on a state of 2 qubits $\rho=|\psi \rangle \langle \psi |$: $$\rho \to (1-\lambda)\rho + \frac{\lambda}{4}I$$ This is within ...
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1answer
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Experiment runtime on IBMQ

I have been trying to get the runtime of my experiment on IBM's quantum computer. I am using the classic stuff, i.e ...
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1answer
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How many physical qubits are used when I run a program on a IBM Q computer?

How do I find out how many physical-qubits I'm using when I run my program in an IBM Q backend quantum computing system?
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2answers
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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 ...
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1answer
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How much variation is there in the results between each quantum computer on the IBMQ Quantum Experience system?

For example, if you ran the same program on the 'ibmqx2' and 'ibmqx4' computers, how much variance would there be between the results from both systems? There is the inherent presence of noise in each ...
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1answer
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Consistent QISkit error: “All devices are currently unavailable”

I am attempting to run the following on a remote backend through QISkit: ...
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Why is there a difference between the simulation results and the actual quantum computer results?

I ran the Grover's Algorithm for 3 Qubits on the IBM Q platform (ibmqx4) and the results of the simulation and the actual computer differ a lot. The screenshots of the circuit and the results are ...
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1answer
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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 ...
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1answer
87 views

Qiskit: 'per shot' result

Is there a way to access the results of measurements 'per shot' performed on a backend such as one of the real IBM machines? I know it can generate a histogram from the cumulative data, but I was ...
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QE error: No handlers could be found for logger

When I run a QASM program on a QE simulator, I get this error. No handlers could be found for logger "IBMQuantumExperience.IBMQuantumExperience" What ...
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1answer
245 views

Why can't I connect to an IBMQ device?

I was trying the qiskit Terra tutorial and it seems that the code provided to connect to an actual quantum computer doesn't run properly. With my API token generated and stored into the variable "...
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1answer
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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. ...
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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: ...
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1answer
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Why can't you run a teleportation circuit on an IBM Q device?

I'm studying teleportation circuits with this tutorial and just out of curiosity, why can't a teleportation circuit be run on an IBM Q device?
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1answer
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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 ...
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1answer
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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 ...
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1answer
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How are Rigetti and IBM QX device parameters related to Kraus operators?

Rigetti reports the following parameters: (https://www.rigetti.com/qpu) T1, T2* times 1-qubit gate fidelity (F1q) 2-qubit gate fidelity (F2q) and, read-out fidelity (Fro) IBM QX reports the ...
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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 ...
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3answers
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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 ...
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1answer
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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^*\\ ...
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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 ...
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1answer
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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 ...
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2answers
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How can I get access to IBM Q 20 Tokyo and IBM Q 20 Austin?

How can I get access to IBM Q 20 Tokyo and IBM Q 20 Austin? In the Q- experience site there is written that the access is for IBM clients only and in the profile there is a "promotional code" that ...
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523 views

Comparing run times on IBM Quantum Experience

I have run this program - ...
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1answer
162 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.
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1answer
516 views

Phase-Shift Gate in Qiskit

How to implement the phase shift gate in qiskit or ibmq? Phase Shift Gate : $$\begin{pmatrix}e^{ia} && 0 \\ 0 && e^{ia}\end{pmatrix} = e^{ia}I$$
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Controlled-U operation in IBMQ

Suppose we have any matrix in $\mathrm U(2)$ and we need to construct a Controlled-$U$ operation with the $H,T,S$ gates. Then I am aware of the construction given in N&C of decomposing $U$ into $e^...
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2answers
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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, ...
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1answer
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How to implement a random selection of one of the 3 qubits on the IBM Q (composer)?

I would like to implement a quantum program on the IBM Composer with following characteristics: The output is the observed value of 3 qubits Only one of the 3 qubits should be observed as $1$, the 2 ...
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How to implement a Square root of Swap gate that swaps 2n-qubits on the IBM Q (composer)?

I am looking for an implementation using the quantum gates provided by the IBM composer of the following quantum function: input $2n$ qubits output $2n$ qubits wherein $50\%$ of the cases the state ...