Update HamiltonianGate path and add tolerance to PulseBackend (qiskit-community#1280)

### Summary

After `qiskit.extensions` was deprecated in
Qiskit/qiskit#10725, this PR updates the path of
`HamiltonianGate` so tests against Qiskit main pass again. This also
adds `atol` and `rtol` tolerance parameters to `PulseBackend` for
speeding up slow tests.

Author: coruscating

qiskit_experiments/test/__init__.py

@@ -37,7 +37,6 @@
     MockIQParallelBackend
     T2HahnBackend
     NoisyDelayAerBackend
-    SingleTransmonTestBackend
 
 Helpers
 =======

qiskit_experiments/test/pulse_backend.py

@@ -72,6 +72,8 @@ def __init__(
         dt: float = 0.1 * 1e-9,
         solver_method="RK23",
         seed: int = 0,
+        atol: float = None,
+        rtol: float = None,
         **kwargs,
     ):
         """Initialize a backend with model information.
@@ -85,6 +87,8 @@ def __init__(
                 methods. Defaults to "RK23".
             seed: An optional seed given to the random number generator. If this argument is not
                 set then the seed defaults to 0.
+            atol: Absolute tolerance during solving.
+            rtol: Relative tolerance during solving.
         """
         from qiskit_dynamics import Solver
 
@@ -109,6 +113,12 @@ def __init__(
 
         self.solver_method = solver_method
 
+        self.solve_kwargs = {}
+        if atol:
+            self.solve_kwargs["atol"] = atol
+        if rtol:
+            self.solve_kwargs["rtol"] = rtol
+
         self.static_hamiltonian = static_hamiltonian
         self.hamiltonian_operators = hamiltonian_operators
         self.static_dissipators = static_dissipators
@@ -339,6 +349,7 @@ def solve(self, schedule: Union[ScheduleBlock, Schedule], qubits: Tuple[int]) ->
             t_eval=[time_f],
             signals=signal,
             method=self.solver_method,
+            **self.solve_kwargs,
         ).y[0]
 
         return unitary
@@ -454,6 +465,8 @@ def __init__(
         lambda_2: float = 0.8e9,
         gamma_1: float = 1e4,
         noise: bool = True,
+        atol: float = None,
+        rtol: float = None,
         **kwargs,
     ):
         """Initialise backend with hamiltonian parameters
@@ -466,6 +479,8 @@ def __init__(
             gamma_1: Relaxation rate (1/T1) for 1-0. Defaults to 1e4.
             noise: Defaults to True. If True then T1 dissipation is included in the pulse-simulation.
                 The strength is given by ``gamma_1``.
+            atol: Absolute tolerance during solving.
+            rtol: Relative tolerance during solving.
         """
         from qiskit_dynamics.pulse import InstructionToSignals
 
@@ -509,6 +524,8 @@ def __init__(
             rwa_cutoff_freq=1.9 * qubit_frequency,
             rwa_carrier_freqs=[qubit_frequency],
             evaluation_mode=evaluation_mode,
+            atol=atol,
+            rtol=rtol,
             **kwargs,
         )
 

releasenotes/notes/0.3/cleanup-cr-hamiltonian-experiment-7f47c51d26941f16.yaml

@@ -6,5 +6,5 @@ upgrade:
     setting backend for just checking experiment sequence. The sequence with actual parameters
     is generated after the backend is set. In addition, now experiments can take ``cr_gate``
     in the constractor which is ``Gate`` type subclass taking a single parameter (flat-top width).
-    If one inputs a :class:`~qiskit.extensions.hamiltonian_gate.HamiltonianGate` subclass with
+    If one inputs a :class:`~qiskit.circuit.library.HamiltonianGate` subclass with
     cross resonance Hamiltonian, experiment can be simulated with Aer QASM simulator.

test/library/calibration/test_half_angle.py

@@ -32,7 +32,7 @@ def setUp(self):
         super().setUp()
         library = FixedFrequencyTransmon()
 
-        self.backend = SingleTransmonTestBackend(noise=False)
+        self.backend = SingleTransmonTestBackend(noise=False, atol=1e-3)
         self.cals = Calibrations.from_backend(self.backend, libraries=[library])
 
     def test_amp_parameter_error(self):

test/library/calibration/test_rabi.py

@@ -34,17 +34,18 @@
 class TestRabiEndToEnd(QiskitExperimentsTestCase):
     """Test the rabi experiment."""
 
-    def setUp(self):
+    @classmethod
+    def setUpClass(cls):
         """Setup the tests."""
-        super().setUp()
+        super().setUpClass()
 
-        self.qubit = 0
+        cls.qubit = 0
 
         with pulse.build(name="x") as sched:
-            pulse.play(pulse.Drag(160, Parameter("amp"), 40, 0.4), pulse.DriveChannel(self.qubit))
+            pulse.play(pulse.Drag(160, Parameter("amp"), 40, 0.4), pulse.DriveChannel(cls.qubit))
 
-        self.sched = sched
-        self.backend = SingleTransmonTestBackend(noise=False)
+        cls.sched = sched
+        cls.backend = SingleTransmonTestBackend(noise=False, atol=1e-3)
 
     # pylint: disable=no-member
     def test_rabi_end_to_end(self):
@@ -101,7 +102,7 @@ def setUp(self):
         super().setUp()
 
         self.qubit = 0
-        self.backend = SingleTransmonTestBackend(noise=False)
+        self.backend = SingleTransmonTestBackend(noise=False, atol=1e-4)
         self.anharmonicity = self.backend.anharmonicity
         with pulse.build(name="x") as sched:
             with pulse.frequency_offset(self.anharmonicity, pulse.DriveChannel(self.qubit)):
@@ -115,7 +116,7 @@ def setUp(self):
     def test_ef_rabi_end_to_end(self):
         """Test the EFRabi experiment end to end."""
 
-        test_tol = 0.01
+        test_tol = 0.05
 
         # Note that the backend is not sophisticated enough to simulate an e-f
         # transition so we run the test with a tiny frequency shift, still driving the e-g transition.

test/library/calibration/test_rough_amplitude.py

@@ -32,7 +32,7 @@ def setUp(self):
         super().setUp()
         library = FixedFrequencyTransmon()
 
-        self.backend = SingleTransmonTestBackend(noise=False)
+        self.backend = SingleTransmonTestBackend(noise=False, atol=1e-3)
         self.cals = Calibrations.from_backend(self.backend, libraries=[library])
 
     def test_circuits(self):
@@ -107,7 +107,7 @@ def setUpClass(cls):
 
         library = FixedFrequencyTransmon()
 
-        cls.backend = SingleTransmonTestBackend(noise=False)
+        cls.backend = SingleTransmonTestBackend(noise=False, atol=1e-3)
         cls.cals = Calibrations.from_backend(cls.backend, libraries=[library])
 
         # Add some pulses on the 1-2 transition.

test/library/calibration/test_rough_frequency.py

@@ -28,7 +28,7 @@ class TestRoughFrequency(QiskitExperimentsTestCase):
     def setUp(self):
         """Setup the tests."""
         super().setUp()
-        self.backend = SingleTransmonTestBackend(noise=False)
+        self.backend = SingleTransmonTestBackend(noise=False, atol=1e-3)
 
     def test_init(self):
         """Test that initialization."""
@@ -53,7 +53,9 @@ def test_update_calibrations(self):
 
         freq01 = BackendData(self.backend).drive_freqs[0]
 
-        backend_5mhz = SingleTransmonTestBackend(qubit_frequency=freq01 + 5e6, noise=False)
+        backend_5mhz = SingleTransmonTestBackend(
+            qubit_frequency=freq01 + 5e6, noise=False, atol=1e-3
+        )
 
         library = FixedFrequencyTransmon()
         cals = Calibrations.from_backend(self.backend, libraries=[library])

test/library/characterization/test_cross_resonance_hamiltonian.py

@@ -21,7 +21,13 @@
 from ddt import ddt, data, unpack
 from qiskit import QuantumCircuit, pulse, qpy, quantum_info as qi
 from qiskit.providers.fake_provider import FakeBogotaV2
-from qiskit.extensions.hamiltonian_gate import HamiltonianGate
+
+# TODO: remove old path after we stop supporting the relevant version of Qiskit
+try:
+    from qiskit.circuit.library.hamiltonian_gate import HamiltonianGate
+except ModuleNotFoundError:
+    from qiskit.extensions.hamiltonian_gate import HamiltonianGate
+
 from qiskit_aer import AerSimulator
 from qiskit_experiments.library.characterization import cr_hamiltonian
 

test/library/characterization/test_multi_state_discrimination.py

@@ -49,7 +49,7 @@ def setUp(self):
         """Setup test variables."""
         super().setUp()
 
-        self.backend = SingleTransmonTestBackend(noise=False)
+        self.backend = SingleTransmonTestBackend(noise=False, atol=1e-3)
 
         # Build x12 schedule
         self.qubit = 0
@@ -94,7 +94,7 @@ def test_discrimination_analysis(self, n_states):
 
         fidelity = exp_data.analysis_results("fidelity").value
 
-        self.assertGreaterEqual(fidelity, 0.96)
+        self.assertGreaterEqual(fidelity, 0.93)
 
         # check that the discriminator differentiates n different states
         discrim_lbls = exp_data.analysis_results("discriminator_config").value["attributes"][