From 3d359ebc1f7013c5b225086cf0bfdc9d2d5965f8 Mon Sep 17 00:00:00 2001
From: Nitin Shivaraman <nitin.shivaraman@gmail.com>
Date: Thu, 5 Oct 2023 15:13:49 +0800
Subject: [PATCH] MPS execution for quimb

---
 setup.py                         |  4 +---
 src/qibotn/quimb.py              | 17 +++++++++++++----
 tests/test_qasm_quimb_backend.py |  8 +++++---
 3 files changed, 19 insertions(+), 10 deletions(-)

diff --git a/setup.py b/setup.py
index 2b1184c..3a690c0 100644
--- a/setup.py
+++ b/setup.py
@@ -41,9 +41,7 @@ setup(
     install_requires=[
         "qibo>=0.1.10",
         "qibojit>=0.0.7",
-        "quimb[tensor]>=1.4.0",
-        "cupy>=11.6.0",
-        "cuquantum-python-cu11",
+        "quimb[tensor]>=1.6.0",
     ],
     extras_require={
         "docs": [],
diff --git a/src/qibotn/quimb.py b/src/qibotn/quimb.py
index 8414540..5f5721b 100644
--- a/src/qibotn/quimb.py
+++ b/src/qibotn/quimb.py
@@ -3,16 +3,25 @@ import quimb.tensor as qtn
 from qibo.models import Circuit as QiboCircuit
 
 
-def from_qibo(circuit: QiboCircuit, psi0=None):
+def from_qibo(circuit: QiboCircuit, is_mps: False, psi0=None, method='svd', 
+              cutoff=1e-6, cutoff_mode='abs'):
     nqubits = circuit.nqubits
-    tncirc = qtn.Circuit(nqubits, psi0=psi0)
+    gate_opt = {}
+    if (is_mps):
+        tncirc = qtn.CircuitMPS(nqubits, psi0=psi0)
+        gate_opt["method"] = method
+        gate_opt["cutoff"] = cutoff
+        gate_opt["cutoff_mode"] = cutoff_mode
+    else:    
+        tncirc = qtn.Circuit(nqubits, psi0=psi0)
 
     for gate in circuit.queue:
         tncirc.apply_gate(
             gate.name,
             *gate.parameters,
             *gate.qubits,
-            parametrize=len(gate.parameters) > 0
+            parametrize=False if is_mps else (len(gate.parameters) > 0),
+            **gate_opt
         )
 
     return tncirc
@@ -32,7 +41,7 @@ def eval(qasm: str, init_state, backend="numpy"):
     """
     circuit = QiboCircuit.from_qasm(qasm)
     init_state_mps = init_state_tn(circuit.nqubits, init_state)
-    circ_quimb = from_qibo(circuit, psi0=init_state_mps)
+    circ_quimb = from_qibo(circuit, is_mps=True, psi0=init_state_mps)
     interim = circ_quimb.psi.full_simplify(seq="DRC")
     amplitudes = interim.to_dense(backend=backend).flatten()
 
diff --git a/tests/test_qasm_quimb_backend.py b/tests/test_qasm_quimb_backend.py
index e962018..3fd756e 100644
--- a/tests/test_qasm_quimb_backend.py
+++ b/tests/test_qasm_quimb_backend.py
@@ -29,8 +29,9 @@ def time(func):
     return time, res
 
 
-@pytest.mark.parametrize("nqubits", [1, 2, 5, 10])
-def test_eval(nqubits: int):
+@pytest.mark.parametrize("nqubits, tolerance",
+                         [(1, 1e-6), (2, 1e-6), (5, 1e-3), (10, 1e-3)])
+def test_eval(nqubits: int, tolerance: float):
     # hack quimb to use the correct number of processes
     # TODO: remove completely, or at least delegate to the backend
     # implementation
@@ -57,4 +58,5 @@ def test_eval(nqubits: int):
     )
 
     assert 1e-2 * qibo_time < quimb_time < 1e2 * qibo_time
-    assert np.allclose(result_sv, result_tn), "Resulting dense vectors do not match"
+    assert np.allclose(result_sv, result_tn,
+                       atol=tolerance), "Resulting dense vectors do not match"