From 802dde6e57e1a372d8395abe28fb14d84d499259 Mon Sep 17 00:00:00 2001
From: vinitha-balachandran <vinitha-balachandran@ihpc.a-star.edu.sg>
Date: Tue, 6 Feb 2024 17:48:53 +0800
Subject: [PATCH] Added class for quimb backend

---
 src/qibotn/backends/cpu.py | 144 +++++++++++++++++++++++++++++++++++++
 1 file changed, 144 insertions(+)
 create mode 100644 src/qibotn/backends/cpu.py

diff --git a/src/qibotn/backends/cpu.py b/src/qibotn/backends/cpu.py
new file mode 100644
index 0000000..d826ba1
--- /dev/null
+++ b/src/qibotn/backends/cpu.py
@@ -0,0 +1,144 @@
+import numpy as np
+
+from qibo.backends.numpy import NumpyBackend
+from qibo.states import CircuitResult
+from qibo.config import raise_error
+
+
+class QuTensorNet(NumpyBackend):  
+
+    def __init__(self, runcard):
+        super().__init__()
+        import quimb  # pylint: disable=import-error
+
+        if runcard is not None:
+            self.MPI_enabled = runcard.get("MPI_enabled", False)
+            self.NCCL_enabled = runcard.get("NCCL_enabled", False)
+            self.expectation_enabled_value = runcard.get("expectation_enabled", False)
+
+
+            mps_enabled_value = runcard.get("MPS_enabled")
+            if mps_enabled_value is True:
+                self.MPS_enabled = True
+            elif mps_enabled_value is False:
+                self.MPS_enabled = False
+            else:
+                raise TypeError("MPS_enabled has an unexpected type")
+
+        else:
+            self.MPI_enabled = False
+            self.MPS_enabled = False
+            self.NCCL_enabled = False
+            self.expectation_enabled = False
+
+        self.name = "qibotn"
+        self.quimb = quimb
+        self.platform = "qutensornet"
+        self.versions["quimb"] = self.quimb.__version__
+   
+
+    def apply_gate(self, gate, state, nqubits):  # pragma: no cover
+        raise_error(NotImplementedError, "QiboTN cannot apply gates directly.")
+
+    def apply_gate_density_matrix(self, gate, state, nqubits):  # pragma: no cover
+        raise_error(NotImplementedError, "QiboTN cannot apply gates directly.")
+
+    def assign_measurements(self, measurement_map, circuit_result):
+        raise_error(NotImplementedError, "Not implemented in QiboTN.")
+
+
+    def set_precision(self, precision):
+        if precision != self.precision:
+            super().set_precision(precision)
+
+
+
+    def execute_circuit(
+        self, circuit, initial_state=None, nshots=None, return_array=False
+    ):  # pragma: no cover
+        """Executes a quantum circuit.
+
+        Args:
+            circuit (:class:`qibo.models.circuit.Circuit`): Circuit to execute.
+            initial_state (:class:`qibo.models.circuit.Circuit`): Circuit to prepare the initial state.
+                If ``None`` the default ``|00...0>`` state is used.
+
+        Returns:
+            xxx.
+
+        """
+
+        import qibotn.eval_qu as eval_qu
+
+        if (
+            self.MPI_enabled == False
+            and self.MPS_enabled == False
+            and self.NCCL_enabled == False
+            and self.expectation_enabled == False
+        ):
+
+            state = eval.dense_vector_tn_qu(circuit, init_state, is_mps=False, backend="numpy")
+
+        elif (
+            self.MPI_enabled == False
+            and self.MPS_enabled == True
+            and self.NCCL_enabled == False
+            and self.expectation_enabled == False
+        ):
+            
+
+            state = eval.dense_vector_tn_qu(circuit, init_state, is_mps=True, backend="numpy")
+
+        elif (
+            self.MPI_enabled == True
+            and self.MPS_enabled == False
+            and self.NCCL_enabled == False
+            and self.expectation_enabled == False
+        ):
+           
+            raise_error(NotImplementedError, "QiboTN quimb backend cannot support MPI.")
+
+
+        elif (
+            self.MPI_enabled == False
+            and self.MPS_enabled == False
+            and self.NCCL_enabled == True
+            and self.expectation_enabled == False
+        ):
+           
+            raise_error(NotImplementedError, "QiboTN quimb backend cannot support NCCL.")
+
+
+        elif (
+            self.MPI_enabled == False
+            and self.MPS_enabled == False
+            and self.NCCL_enabled == False
+            and self.expectation_enabled == True
+        ):
+           
+            raise_error(NotImplementedError, "QiboTN quimb backend cannot support expectation")
+
+
+        elif (
+            self.MPI_enabled == True
+            and self.MPS_enabled == False
+            and self.NCCL_enabled == False
+            and self.expectation_enabled == True
+        ):
+            raise_error(NotImplementedError, "QiboTN quimb backend cannot support expectation")
+
+        elif (
+            self.MPI_enabled == False
+            and self.MPS_enabled == False
+            and self.NCCL_enabled == True
+            and self.expectation_enabled == True
+        ):
+            raise_error(NotImplementedError, "QiboTN quimb backend cannot support expectation")
+        else:
+            raise_error(NotImplementedError, "Compute type not supported.")
+
+        if return_array:
+            return state.flatten()
+        else:
+            circuit._final_state = CircuitResult(self, circuit, state.flatten(), nshots)
+            return circuit._final_state