This circuit creates two entangled Bell pairs and then performs entanglement swapping through a Bell state measurement.
```python
from qiskit import QuantumCircuit
# Create a circuit with 4 qubits and 2 classical bits
qc = QuantumCircuit(4, 2)
# Create two entangled pairs (Bell states)
# First Bell pair between qubits 0 and 1
qc.h(0)
qc.cx(0, 1)
# Second Bell pair between qubits 2 and 3
qc.h(2)
qc.cx(2, 3)
# Perform a Bell state measurement on qubits 1 and 2 (Entanglement Swapping)
qc.cx(1, 2)
qc.h(1)
qc.measure([1, 2], [0, 1])
```'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"}]}\''