This circuit initializes four qubits to the |+⟩ state, forms a ring cluster state using controlled-Z gates, and then measures all qubits.
```python
from qiskit import *
# Create circuit with 4 qubits and 4 classical bits
qc = QuantumCircuit(4, 4)
# Initialize all qubits to the |+⟩ state
qc.h([0, 1, 2, 3])
# Apply controlled-Z gates in a ring topology to create a ring cluster state
qc.cz(0, 1)
qc.cz(1, 2)
qc.cz(2, 3)
qc.cz(3, 0)
# Measure all qubits
qc.measure([0, 1, 2, 3], [0, 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"}]}\''