AttributeError when trying to create a DynamicsBackend:
File ~/envs/qiskit/lib/python3.12/site-packages/qiskit_dynamics/backend/dynamics_backend.py:219, in DynamicsBackend.__init__(self, solver, target, **options)
216 target.add_instruction(Measure(), measure_properties)
218 target.dt = solver._dt
--> 219 target.num_qubits = len(self.options.subsystem_dims)
221 self._target = target
AttributeError: attribute 'num_qubits' of 'qiskit._accelerate.target.BaseTarget' objects is not writable
Steps to reproduce the problem
Run the following code with Qiskit 1.3:
from qiskit.quantum_info import Operator
from qiskit_dynamics import DynamicsBackend, Solver
import numpy as np
nu_z = 10.
nu_x = 1.
nu_d = 9.98 # Almost on resonance with the Hamiltonian's energy levels difference, nu_z
X = Operator.from_label('X')
Y = Operator.from_label('Y')
Z = Operator.from_label('Z')
s_p = 0.5 * (X + 1j * Y)
solver = Solver(
static_hamiltonian=.5 * 2 * np.pi * nu_z * Z,
hamiltonian_operators=[2 * np.pi * nu_x * X],
hamiltonian_channels=["d0"],
channel_carrier_freqs={"d0": nu_x},
dt=0.01,
)
dynamics_backend = DynamicsBackend(solver=solver, subsystem_dims=[2])
What is the expected behavior?
Successful DynamicsBackend creation
Suggested solutions
num_qubits can be passed to Target instead. I am not sure about the case when a target is passed in to DynamicsBackend. ~I think it should just leave the target alone and base the number of qubits on the subsystem dimensions. Perhaps it could make a new target and only copy the instructions related to the qubits in the subsystem.~ Thinking about it more, I think it would be most consistent to build a new qubit with just the instructions for the qubits in the subsystem to be simulated. Otherwise, number of qubits will be inconsistent in different parts of the code.
Informations
What is the current behavior?
AttributeErrorwhen trying to create aDynamicsBackend:Steps to reproduce the problem
Run the following code with Qiskit 1.3:
What is the expected behavior?
Successful
DynamicsBackendcreationSuggested solutions
num_qubitscan be passed toTargetinstead. I am not sure about the case when a target is passed in toDynamicsBackend. ~I think it should just leave the target alone and base the number of qubits on the subsystem dimensions. Perhaps it could make a new target and only copy the instructions related to the qubits in the subsystem.~ Thinking about it more, I think it would be most consistent to build a new qubit with just the instructions for the qubits in the subsystem to be simulated. Otherwise, number of qubits will be inconsistent in different parts of the code.