Create circuit from qiskit json format

Question

When you run a job on an IBM device you can download a json file which contains among other things the description of the circuit. Is there a simple way in qiskit to create a QuantumCircuit object from this file without writing your own parser?

Below is an example for the content of this file.

{"config": {"n_qubits": 5, "memory_slots": 3}, "header": {"qubit_labels": [["q", 0], ["q", 1], ["q", 2], ["q", 3], ["q", 4]], "n_qubits": 5, "qreg_sizes": [["q", 5]], "clbit_labels": [["meas", 0], ["meas", 1], ["meas", 2]], "memory_slots": 3, "creg_sizes": [["meas", 3]], "name": "circuit-103", "global_phase": 2.356194490192345, "metadata": {}}, "instructions": [{"name": "rz", "params": [1.5707963267948966], "qubits": [0]}, {"name": "sx", "qubits": [0]}, {"name": "rz", "params": [1.5707963267948966], "qubits": [0]}, {"name": "rz", "params": [1.5707963267948966],...

Answer 1

The format that the IBM Quantum API is currently using is Qobj (or Quantum object) which is documented here: https://arxiv.org/abs/1809.03452 and the current schema definitions for it are located here: https://github.com/Qiskit/ibm-quantum-schemas

That's just the background information on the format though, to answer the details of your question, Qiskit supports loading this and creating a circuit from a Qobj payload via its Qobj class and the disassemble() function. Assuming you have a local file job.json the basic workflow would be something like:

import json

from qiskit.assembler.disassemble import disassemble
from qiskit.qobj import QasmQobj

with open('job.json') as fd:
    qobj_dict = json.load(fd)
qobj = QasmQobj.from_dict(qobj_dict)
circuits, run_config, headers = disassemble(qobj)

Where circuits is the list of QuantumCircuit objects equivalent to what's in the qobj (a qobj can contain more than one circuit).

run_config and headers are dictionaries containing the configuration and metadata contained in the qobj.