From afdb69289136cdf3d65e7d030781f617435c3699 Mon Sep 17 00:00:00 2001
From: Douglas Wilson <douglas.wilson@quantinuum.com>
Date: Tue, 22 Aug 2023 08:46:10 +0100
Subject: [PATCH] TKET-3469 Allow setting of RNG seed

---
 .../qulacs/backends/qulacs_backend.py         | 20 +++++++++++++++----
 tests/test_qulacs_backend.py                  |  4 ++--
 2 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/pytket/extensions/qulacs/backends/qulacs_backend.py b/pytket/extensions/qulacs/backends/qulacs_backend.py
index 859383e..0c1ca41 100644
--- a/pytket/extensions/qulacs/backends/qulacs_backend.py
+++ b/pytket/extensions/qulacs/backends/qulacs_backend.py
@@ -17,6 +17,7 @@
 
 from typing import List, Optional, Sequence, Union
 from logging import warning
+from random import Random
 from uuid import uuid4
 import numpy as np
 from sympy import Expr  # type: ignore
@@ -104,8 +105,9 @@ class QulacsBackend(Backend):
         *_1Q_GATES,
         OpType.Barrier,
     }
+    _seed = None
 
-    def __init__(self) -> None:
+    def __init__(self, seed: Optional[int] = None) -> None:
         super().__init__()
         self._backend_info = BackendInfo(
             type(self).__name__,
@@ -116,6 +118,8 @@ def __init__(self) -> None:
         )
 
         self._sim = QuantumState
+        if seed:
+            self._seed = Random(seed)
 
     @property
     def _result_id_type(self) -> _ResultIdTuple:
@@ -205,7 +209,7 @@ def process_circuits(
                 else:
                     bits, choose_indices = zip(*bits2index)
 
-                    samples = qulacs_state.sampling(n_shots_circ)
+                    samples = self._sample_quantum_state(qulacs_state, n_shots_circ)
                     shots = OutcomeArray.from_ints(samples, circuit.n_qubits)
                     shots = shots.choose_indices(choose_indices)
             try:
@@ -228,6 +232,14 @@ def process_circuits(
             del qulacs_circ
         return handle_list
 
+    def _sample_quantum_state(
+        self, quantum_state: QuantumState, n_shots: int
+    ) -> List[int]:
+        if self._seed:
+            return quantum_state.sampling(n_shots, self._seed.randint(0, 2**32 - 1))
+        else:
+            return quantum_state.sampling(n_shots)
+
     def circuit_status(self, handle: ResultHandle) -> CircuitStatus:
         if handle in self._cache:
             return CircuitStatus(StatusEnum.COMPLETED)
@@ -286,7 +298,7 @@ class QulacsGPUBackend(QulacsBackend):
         Backend for running simulations on the Qulacs GPU simulator
         """
 
-        def __init__(self) -> None:
-            super().__init__()
+        def __init__(self, **kwargs) -> None:
+            super().__init__(**kwargs)
             self._backend_info.name = type(self).__name__
             self._sim = QuantumStateGpu
diff --git a/tests/test_qulacs_backend.py b/tests/test_qulacs_backend.py
index 8e251ff..02bded2 100644
--- a/tests/test_qulacs_backend.py
+++ b/tests/test_qulacs_backend.py
@@ -26,12 +26,12 @@
 from pytket.utils.operators import QubitPauliOperator
 from pytket.extensions.qulacs import QulacsBackend
 
-backends = [QulacsBackend()]
+backends = [QulacsBackend(), QulacsBackend(seed=-1)]
 
 try:
     from pytket.extensions.qulacs import QulacsGPUBackend
 
-    backends.append(QulacsGPUBackend())
+    backends.append([QulacsGPUBackend(), QulacsGPUBackend(seed=1)])
 except ImportError:
     warnings.warn("local settings failed to import QulacsGPUBackend", ImportWarning)