Switch default backend to qutip, remove projectq dependency from CI

Examples use stabilizer explicitly for speed; global default is now
qutip so students can use non-Clifford gates without confusion.
Also fixes numpy deprecation warning in qutip_simulator.py.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: Stephanie Wehner

examples/new-sdk/corrRNG/simulaqron_settings.json

@@ -7,7 +7,7 @@
     "recv_retry_time": 0.1,
     "recv_max_retries": 10,
     "log_level": 30,
-    "sim_backend": "projectq",
+    "sim_backend": "stabilizer",
     "noisy_qubits": false,
     "max_app_waiting_time": -1.0,
     "t1": 1.0

examples/new-sdk/extendGHZ/simulaqron_settings.json

@@ -7,7 +7,7 @@
     "recv_retry_time": 0.1,
     "recv_max_retries": 10,
     "log_level": 30,
-    "sim_backend": "projectq",
+    "sim_backend": "stabilizer",
     "noisy_qubits": false,
     "max_app_waiting_time": -1.0,
     "t1": 1.0

examples/new-sdk/teleport/simulaqron_settings.json

@@ -7,7 +7,7 @@
     "recv_retry_time": 0.1,
     "recv_max_retries": 10,
     "log_level": 30,
-    "sim_backend": "projectq",
+    "sim_backend": "stabilizer",
     "noisy_qubits": false,
     "max_app_waiting_time": -1.0,
     "t1": 1.0

examples/new-sdk/template-client-server/simulaqron_settings.json

@@ -7,7 +7,7 @@
     "recv_retry_time": 0.1,
     "recv_max_retries": 10,
     "log_level": 30,
-    "sim_backend": "projectq",
+    "sim_backend": "stabilizer",
     "noisy_qubits": false,
     "max_app_waiting_time": -1.0,
     "t1": 1.0

examples/new-sdk/template-quantum-local/simulaqron_settings.json

@@ -7,7 +7,7 @@
     "recv_retry_time": 0.1,
     "recv_max_retries": 10,
     "log_level": 30,
-    "sim_backend": "projectq",
+    "sim_backend": "stabilizer",
     "noisy_qubits": false,
     "max_app_waiting_time": -1.0,
     "t1": 1.0

simulaqron/run/run.py

@@ -117,7 +117,7 @@ def run_applications(
         network_cfg: Union[str, PathLike, Path] = None,  # WARNING - The type of this argument *cannot* be harmonized
         nv_cfg: Any = None,  # Unused; it's here for harmonization with squidasm "simulate_application"
         log_cfg: LogConfig = None,
-        formalism: Formalism = Formalism.KET,
+        formalism: Formalism = Formalism.DM,
         use_app_config: bool = True,
         post_function: Optional[Callable] = None,
         enable_logging: bool = True,

simulaqron/settings/simulaqron_config.py

@@ -76,7 +76,7 @@ class SimulaqronConfig(JSONSerializerMixin):
     recv_retry_time: float = 0.1
     recv_max_retries: int = 10
     log_level: int = logging.WARNING
-    sim_backend: SimBackend = SimBackend.STABILIZER
+    sim_backend: SimBackend = SimBackend.QUTIP
     noisy_qubits: bool = False
     max_app_waiting_time: float = -1.0  # In seconds, negative means unlimited waiting
     t1: float = 1.0
@@ -152,7 +152,7 @@ def default_settings(self):
         * recv_retry_time = 0.1
         * recv_max_retries = 10
         * log_level = logging.WARNING
-        * sim_backend = SimBackend.STABILIZER
+        * sim_backend = SimBackend.QUTIP
         * noisy_qubits = False
         * max_app_waiting_time = -1.0  # In seconds, negative means unlimited waiting
         * t1: float = 1.0

simulaqron/virtual_node/qutip_simulator.py

@@ -427,7 +427,7 @@ def measure_qubit_inplace(self, qubitNum: int):
             p0, p1 = 0.5, 0.5
 
         # Sample the measurement outcome from these probabilities
-        outcome = int(np.random.choice([0, 1], 1, p=[p0, p1]))
+        outcome = np.random.choice([0, 1], p=[p0, p1]).item()
 
         # Compute the post-measurement state, getting rid of the measured qubit
         if outcome == 0:

tests/quick/general/test_classical_sockets.py

@@ -11,7 +11,7 @@ class TestClassicalSocket:
     @pytest.fixture(autouse=True)
     def configurations(self):
         simulaqron_settings.default_settings()
-        simulaqron_settings.sim_backend = SimBackend.PROJECTQ
+        simulaqron_settings.sim_backend = SimBackend.STABILIZER
         network_config.using_default_network()
         yield
 

tests/quick/netqasm/test_get_qubit_state.py

@@ -21,7 +21,7 @@ class TestGetQubitState:
     @pytest.fixture(autouse=True)
     def reset_configs(self):
         simulaqron_settings.default_settings()
-        simulaqron_settings.sim_backend = SimBackend.PROJECTQ
+        simulaqron_settings.sim_backend = SimBackend.QUTIP
         network_config.using_default_network()
 
     # Here we define the quantum programs used in the tests