Running the program in Quantum Lab, it shows error. I am looking for solution.

Here is a code I run:

circ = QuantumCircuit(3)


circ.cx(0, 1)

circ.cx(0, 2)

from qiskit import Aer

backend = Aer.get_backend('statevector_simulator')
job = execute(circ, backend)
result = job.result()   
outputstate =result.get_statevector(circ, decimals=3)

An here is an error I got:

NameError                                 Traceback (most recent call last)
<ipython-input-3-17b8e431afa9> in <module>

----> 1 circ = QuantumCircuit(3)

      2 # Add a H gate on qubit 0, putting this qubit in superposition.

      3 circ.h(0)

      4 # Add a CX (CNOT) gate on control qubit 0 and target qubit 1, putting

      5 # the qubits in a Bell state.

NameError: name 'QuantumCircuit' is not defined

1 Answer 1


You need to import QuantumCircuit from qiskit:

from qiskit import QuantumCircuit

I imagine you will probably also need to do:

from qiskit import execute

And you can combine your three imports neatly into one line like so:

from qiskit import Aer, QuantumCircuit, execute
  • $\begingroup$ thanx u solved my problem. got the results $\endgroup$
    – parth
    Sep 8, 2020 at 11:03

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