MPS emulator for LUCJ circuits

docs/api/ffsim.tenpy.rst

@@ -0,0 +1,7 @@
+ffsim.tenpy
+===========
+
+.. automodule:: ffsim.tenpy
+   :members:
+   :special-members:
+   :show-inheritance:

docs/api/index.md

@@ -9,5 +9,6 @@ ffsim.linalg
 ffsim.optimize
 ffsim.qiskit
 ffsim.random
+ffsim.tenpy
 ffsim.testing
 ```

docs/how-to-guides/index.md

@@ -4,6 +4,7 @@
 :maxdepth: 1
 
 lucj
+lucj_mps
 entanglement-forging
 fermion-operator
 qiskit-circuits

pyproject.toml

@@ -26,6 +26,7 @@ dependencies = [
     "numpy",
     "opt_einsum",
     "orjson",
+    "physics-tenpy",
     "pyscf >= 2.7",
     "qiskit >= 1.1",
     "scipy",

python/ffsim/__init__.py

@@ -10,7 +10,7 @@
 
 """ffsim is a software library for fast simulation of fermionic quantum circuits."""
 
-from ffsim import contract, linalg, optimize, qiskit, random, testing
+from ffsim import contract, linalg, optimize, qiskit, random, tenpy, testing
 from ffsim.cistring import init_cache
 from ffsim.gates import (
     apply_diag_coulomb_evolution,
@@ -189,6 +189,7 @@
     "spin_square",
     "strings_to_addresses",
     "strings_to_indices",
+    "tenpy",
     "testing",
     "trace",
 ]

python/ffsim/hamiltonians/molecular_hamiltonian.py

@@ -20,11 +20,13 @@
 from opt_einsum import contract
 from pyscf.fci.direct_nosym import absorb_h1e, contract_2e, make_hdiag
 from scipy.sparse.linalg import LinearOperator
+from tenpy.networks.mpo import MPO
 from typing_extensions import deprecated
 
 from ffsim.cistring import gen_linkstr_index
 from ffsim.operators import FermionOperator, cre_a, cre_b, des_a, des_b
 from ffsim.states import dim
+from ffsim.tenpy.hamiltonians import MolecularHamiltonianMPOModel
 
 
 @dataclasses.dataclass(frozen=True)
@@ -120,6 +122,40 @@ def rotated(self, orbital_rotation: np.ndarray) -> MolecularHamiltonian:
             constant=self.constant,
         )
 
+    def to_mpo(self, decimal_places: int | None = None) -> MPO:
+        r"""Return the Hamiltonian as an MPO.
+
+        Args:
+            decimal_places: The number of decimal places to which to round the input
+                one-body and two-body tensors.
+
+                .. note::
+                    Rounding may reduce the MPO bond dimension.
+
+        Returns:
+            The Hamiltonian as an MPO.
+        """
+
+        if decimal_places:
+            one_body_tensor = np.round(self.one_body_tensor, decimals=decimal_places)
+            two_body_tensor = np.round(self.two_body_tensor, decimals=decimal_places)
+        else:
+            one_body_tensor = self.one_body_tensor
+            two_body_tensor = self.two_body_tensor
+
+        model_params = dict(
+            cons_N="N",
+            cons_Sz="Sz",
+            L=1,
+            norb=self.norb,
+            one_body_tensor=one_body_tensor,
+            two_body_tensor=two_body_tensor,
+            constant=self.constant,
+        )
+        mpo_model = MolecularHamiltonianMPOModel(model_params)
+
+        return mpo_model.H_MPO
+
     def _linear_operator_(self, norb: int, nelec: tuple[int, int]) -> LinearOperator:
         """Return a SciPy LinearOperator representing the object."""
         n_alpha, n_beta = nelec

python/ffsim/tenpy/__init__.py

@@ -0,0 +1,39 @@
+# (C) Copyright IBM 2024.
+#
+# This code is licensed under the Apache License, Version 2.0. You may
+# obtain a copy of this license in the LICENSE.txt file in the root directory
+# of this source tree or at http://www.apache.org/licenses/LICENSE-2.0.
+#
+# Any modifications or derivative works of this code must retain this
+# copyright notice, and modified files need to carry a notice indicating
+# that they have been altered from the originals.
+
+"""Code that uses TeNPy, e.g. for emulating quantum circuits."""
+
+from ffsim.tenpy.circuits.gates import (
+    cphase1,
+    cphase2,
+    gate1,
+    gate2,
+    phase,
+    sym_cons_basis,
+    xy,
+)
+from ffsim.tenpy.circuits.lucj_circuit import lucj_circuit_as_mps
+from ffsim.tenpy.hamiltonians.lattices import MolecularChain
+from ffsim.tenpy.hamiltonians.molecular_hamiltonian import MolecularHamiltonianMPOModel
+from ffsim.tenpy.util import product_state_as_mps
+
+__all__ = [
+    "cphase1",
+    "cphase2",
+    "gate1",
+    "gate2",
+    "lucj_circuit_as_mps",
+    "MolecularChain",
+    "MolecularHamiltonianMPOModel",
+    "phase",
+    "product_state_as_mps",
+    "sym_cons_basis",
+    "xy",
+]

python/ffsim/tenpy/circuits/__init__.py

@@ -0,0 +1,9 @@
+# (C) Copyright IBM 2024.
+#
+# This code is licensed under the Apache License, Version 2.0. You may
+# obtain a copy of this license in the LICENSE.txt file in the root directory
+# of this source tree or at http://www.apache.org/licenses/LICENSE-2.0.
+#
+# Any modifications or derivative works of this code must retain this
+# copyright notice, and modified files need to carry a notice indicating
+# that they have been altered from the originals.