clerusch commented 7 months ago

Environment information

mqt.qecc version 1.5.0
qiskit version 0.45.1 (also the case with the simulator from our project, qrisp, but for best reproducability I included a qiskit file so you can check the issue)

Description

The error corrected circuit has incorrect output when measuring Z on all data qubits. Therefore, the ECC protocol does not work.

Expected behavior

Correct encoding resulting in correct logical qubit when measuring data qubits

How to Reproduce

run the following python code. This circuit should result in an always measurement outcome of 1.


from mqt import qecc
from qiskit import QuantumCircuit, Aer, execute, ClassicalRegister
from qiskit.compiler import transpile

file = "./minimalbeispielsource.qasm" ecc = "Q7Steane" ecc_frequency = 10 qc = QuantumCircuit(1) qc.x(0) qc.qasm(filename=file) result = qecc.apply_ecc(file, ecc, ecc_frequency) circ = QuantumCircuit.from_qasm_str(result["circ"])

cr = ClassicalRegister(1,'my_reg')

measure encoded logical qubit by measuring logical Z = ZZZZZZZ

circ.add_register(cr) for i in range(7): circ.measure(circ.qubits[i],cr)

simulator = Aer.get_backend('qasm_simulator')

Transpile the circuit for the simulator

transpiled_circuit = transpile(circ, simulator)

Run the simulation

job = execute(transpiled_circuit, simulator, shots=1024, optimization_level=0) # You can adjust the number of shots as needed result = job.result()

Get the counts from the simulation results

counts = result.get_counts()

get the measurement outcomes

states = [k for k, _ in counts.items()]

get the logical measurement results for encoded qubit

res0, res1 = 0, 0 for state in states: if state[0] == '0': res0 += counts[state] elif state[0] == '1': res1 += counts[state] print(states) print(f"We got 0 {res0} times and 1 {res1} times")

burgholzer commented 7 months ago

Thanks for the report and the reproducer. That definitely looks like a bug. @33Gjl1Xe could you maybe take a look?