This circuit encodes a qubit into a three-qubit entangled state, introduces an error, then uses syndrome measurement to detect and correct the error.
```python
from qiskit import QuantumCircuit
# Create a QuantumCircuit with 4 qubits and 4 classical bits
qc = QuantumCircuit(4, 4)
# Assume qubit 0 is initialized to an arbitrary state |ψ⟩
# Encoding circuit to detect arbitrary single-qubit errors
# Put qubits 1, 2, and 3 into superposition
qc.h(1)
qc.h(2)
qc.h(3)
# Entangle qubit 0 with qubits 1, 2, and 3
qc.cx(0, 1)
qc.cx(0, 2)
qc.cx(0, 3)
# Introduce an error on qubit 2 (for demonstration)
qc.x(2)
# Syndrome measurement to detect errors
qc.cx(1, 0)
qc.cx(2, 0)
qc.cx(3, 0)
qc.measure(0, 0)
# Measure the data qubits
qc.measure([1, 2, 3], [1, 2, 3])
```'Failed to run program: \'409 Client Error: Conflict for url: https://api.quantum.ibm.com/runtime/jobs. {"errors":[{"message":"You have reached the limit of 3 pending jobs. Please wait for a job to complete or cancel one before submitting anything new.","code":3458,"solution":"Wait until some previous jobs were finished. You can cancel pending jobs to run new jobs.","more_info":"https://docs.quantum-computing.ibm.com/errors"}]}\''