fetchOutput

Retrieve result of quantum task

Since R2023a

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Syntax

m = fetchOutput(task)

Description

Add-On Required: This feature requires the MATLAB Support Package for Quantum Computing add-on.

m = fetchOutput(task) returns the measurement result of a finished quantum task.

A measurement result is obtained only if the status of the task is "finished" and the task is not canceled. You can use wait(task) to make sure a task is finished before retrieving the measurement result using fetchOutput.

example

Examples

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Create a quantum circuit that consists of a Hadamard gate and a controlled X gate to entangle two qubits.

gates = [hGate(1); cxGate(1,2)];
c = quantumCircuit(gates);

Connect to a remote quantum device through AWS®. Create a task that runs the circuit on the device.

dev = quantum.backend.QuantumDeviceAWS("Aspen-M-3");
task = run(c,dev)
task = 

  QuantumTaskAWS with properties:

    TaskARN: "arn:aws:braket:us-west-1:123456789012:quantum-task/12a34b5c-6a78-9a01-2ab3-4c56def7g890"
     Status: "queued"

Wait for the task to finish and retrieve the result.

wait(task)
m = fetchOutput(task)
m = 

  QuantumMeasurement with properties:

    MeasuredStates: [4×1 string]
            Counts: [4×1 double]
     Probabilities: [4×1 double]
         NumQubits: 2

Show the counts and estimated probabilities of the measured states.

table(m.Counts,m.Probabilities,m.MeasuredStates, ...
    VariableNames=["Counts","Probabilities","States"])
ans =

  4×3 table

    Counts    Probabilities    States
    ______    _____________    ______

      47          0.47          "00" 
       2          0.02          "10" 
       5          0.05          "01" 
      46          0.46          "11"

Plot these measured states as a histogram of estimated probabilities.

histogram(m)

Histogram of estimated probabilities of the measured states

Create a quantum circuit that consists of a Hadamard gate and a controlled X gate to entangle two qubits.

gates = [hGate(1); cxGate(1,2)];
c = quantumCircuit(gates);

Connect to a remote quantum device through the IBM® Qiskit® Runtime Services. Create a task that runs the circuit on the device using error mitigation.

dev = quantum.backend.QuantumDeviceIBM("ibm_fez");
task = run(c,dev,UseErrorMitigation=true)
task = 

  QuantumTaskIBM with properties:

         TaskID: "abc123456d7abcde012f"
      SessionID: <missing>
    AccountName: "some_account_name"
         Status: "queued"

Wait for the task to finish and retrieve the result.

wait(task)
m = fetchOutput(task)
m = 

  QuantumMeasurement with properties:

    MeasuredStates: [4×1 string]
            Counts: [4×1 double]
     Probabilities: [4×1 double]
         NumQubits: 2

Plot the measured states as a histogram of estimated probabilities.

histogram(m)

Histogram of estimated probabilities of the measured states

Input Arguments

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Finished quantum task, specified as a QuantumTaskAWS or a QuantumTaskIBM object. The Status property of this QuantumTaskAWS or QuantumTaskIBM object must be "finished".

Output Arguments

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Measurement result, returned as a numeric vector or a QuantumMeasurement object. If the quantum task input was created using the run function with a specified Observable name-value argument, then the fetchOutput function returns the measurement result as a numeric expectation value. Otherwise, the fetchOutput function returns the measurement result as a QuantumMeasurement object.

Version History

Introduced in R2023a

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See Also

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