Create a bloq for Semi-Classical QFT

dev_tools/qualtran_dev_tools/notebook_specs.py

@@ -701,6 +701,11 @@
         module=qualtran.bloqs.qft.qft_phase_gradient,
         bloq_specs=[qualtran.bloqs.qft.qft_phase_gradient._QFT_PHASE_GRADIENT_DOC],
     ),
+    NotebookSpecV2(
+        title='Semi-Classical QFT',
+        module=qualtran.bloqs.qft.semi_classical_qft,
+        bloq_specs=[qualtran.bloqs.qft.semi_classical_qft._SEMI_CLASSICAL_QFT_DOC],
+    ),
     # --------------------------------------------------------------------------
     # -----   Phase Estimation          ----------------------------------------
     # --------------------------------------------------------------------------

docs/bloqs/index.rst

@@ -122,6 +122,7 @@ Bloqs Library
     qft/approximate_qft.ipynb
     qft/qft_text_book.ipynb
     qft/qft_phase_gradient.ipynb
+    qft/semi_classical_qft.ipynb
     phase_estimation/lp_resource_state.ipynb
     phase_estimation/text_book_qpe.ipynb
     phase_estimation/kaiser_window_state.ipynb

qualtran/bloqs/qft/__init__.py

@@ -14,4 +14,5 @@
 from .approximate_qft import ApproximateQFT
 from .qft_phase_gradient import QFTPhaseGradient
 from .qft_text_book import QFTTextBook
+from .semi_classical_qft import SemiClassicalQFT
 from .two_bit_ffft import TwoBitFFFT

qualtran/bloqs/qft/semi_classical_qft.ipynb

@@ -0,0 +1,155 @@
+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "id": "de9c5ff4",
+   "metadata": {
+    "cq.autogen": "title_cell"
+   },
+   "source": [
+    "# Semi-Classical QFT"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "70368002",
+   "metadata": {
+    "cq.autogen": "top_imports"
+   },
+   "outputs": [],
+   "source": [
+    "from qualtran import Bloq, CompositeBloq, BloqBuilder, Signature, Register\n",
+    "from qualtran import QBit, QInt, QUInt, QAny\n",
+    "from qualtran.drawing import show_bloq, show_call_graph, show_counts_sigma\n",
+    "from typing import *\n",
+    "import numpy as np\n",
+    "import sympy\n",
+    "import cirq"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "f7a1c4c5",
+   "metadata": {
+    "cq.autogen": "SemiClassicalQFT.bloq_doc.md"
+   },
+   "source": [
+    "## `SemiClassicalQFT`\n",
+    "Represents QFT followed by measurement.\n",
+    "\n",
+    "When QFT is followed by measurement, we can replace all two qubit gates with classically\n",
+    "controlled Rz rotations (at most $n-1$ Rz rotations). The two structures (QFT + Measurement)\n",
+    "and SemiClassicaQFT behave statistically the same.\n",
+    "\n",
+    "\n",
+    "#### Registers\n",
+    " - `q`: A `QUInt` of `bitsize` qubits on which the QFT is performed and then measured. \n",
+    "\n",
+    "#### Parameters\n",
+    " - `bitsize`: Size of the input register to apply QFT on.\n",
+    " - `is_adjoint`: Whether to apply QFT or QFT†. \n",
+    "\n",
+    "#### References\n",
+    " - [Semiclassical Fourier Transform for Quantum Computation, Griffiths & Niu](https://arxiv.org/abs/quant-ph/9511007). \n",
+    " - [Implementation of the Semiclassical Quantum Fourier Transform in a Scalable System](https://www.science.org/doi/10.1126/science.1110335). \n",
+    " - [stackexchange answer, Gidney](https://quantumcomputing.stackexchange.com/a/23712). \n"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "6da027d2",
+   "metadata": {
+    "cq.autogen": "SemiClassicalQFT.bloq_doc.py"
+   },
+   "outputs": [],
+   "source": [
+    "from qualtran.bloqs.qft import SemiClassicalQFT"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "649aaa69",
+   "metadata": {
+    "cq.autogen": "SemiClassicalQFT.example_instances.md"
+   },
+   "source": [
+    "### Example Instances"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "6d39d25c",
+   "metadata": {
+    "cq.autogen": "SemiClassicalQFT.semi_classical_qft"
+   },
+   "outputs": [],
+   "source": [
+    "semi_classical_qft = SemiClassicalQFT(3)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "c2f31d47",
+   "metadata": {
+    "cq.autogen": "SemiClassicalQFT.graphical_signature.md"
+   },
+   "source": [
+    "#### Graphical Signature"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "3ac8fb19",
+   "metadata": {
+    "cq.autogen": "SemiClassicalQFT.graphical_signature.py"
+   },
+   "outputs": [],
+   "source": [
+    "from qualtran.drawing import show_bloqs\n",
+    "show_bloqs([semi_classical_qft],\n",
+    "           ['`semi_classical_qft`'])"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "bd0754a1",
+   "metadata": {
+    "cq.autogen": "SemiClassicalQFT.call_graph.md"
+   },
+   "source": [
+    "### Call Graph"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "44d351d0",
+   "metadata": {
+    "cq.autogen": "SemiClassicalQFT.call_graph.py"
+   },
+   "outputs": [],
+   "source": [
+    "from qualtran.resource_counting.generalizers import ignore_split_join\n",
+    "semi_classical_qft_g, semi_classical_qft_sigma = semi_classical_qft.call_graph(max_depth=1, generalizer=ignore_split_join)\n",
+    "show_call_graph(semi_classical_qft_g)\n",
+    "show_counts_sigma(semi_classical_qft_sigma)"
+   ]
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Python 3",
+   "language": "python",
+   "name": "python3"
+  },
+  "language_info": {
+   "name": "python"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 5
+}

qualtran/bloqs/qft/semi_classical_qft.py

@@ -0,0 +1,71 @@
+#  Copyright 2025 Google LLC
+#
+#  Licensed under the Apache License, Version 2.0 (the "License");
+#  you may not use this file except in compliance with the License.
+#  You may obtain a copy of the License at
+#
+#      https://www.apache.org/licenses/LICENSE-2.0
+#
+#  Unless required by applicable law or agreed to in writing, software
+#  distributed under the License is distributed on an "AS IS" BASIS,
+#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#  See the License for the specific language governing permissions and
+#  limitations under the License.
+
+from functools import cached_property
+from typing import TYPE_CHECKING
+
+import attrs
+
+from qualtran import Bloq, bloq_example, BloqDocSpec, QUInt, Register, Side, Signature
+from qualtran.bloqs.basic_gates import Hadamard, Rz
+from qualtran.bloqs.basic_gates._shims import Measure
+from qualtran.resource_counting import BloqCountDictT, SympySymbolAllocator
+
+if TYPE_CHECKING:
+    from qualtran.symbolics import SymbolicInt
+
+
+@attrs.frozen
+class SemiClassicalQFT(Bloq):
+    r"""Represents QFT followed by measurement.
+
+    When QFT is followed by measurement, we can replace all two qubit gates with classically
+    controlled Rz rotations (at most $n-1$ Rz rotations). The two structures (QFT + Measurement)
+    and SemiClassicaQFT behave statistically the same.
+
+
+    Registers:
+        q: A `QUInt` of `bitsize` qubits on which the QFT is performed and then measured.
+
+    Args:
+        bitsize: Size of the input register to apply QFT on.
+        is_adjoint: Whether to apply QFT or QFT†.
+
+    References:
+        [Semiclassical Fourier Transform for Quantum Computation, Griffiths & Niu](https://arxiv.org/abs/quant-ph/9511007)
+
+        [Implementation of the Semiclassical Quantum Fourier Transform in a Scalable System](https://www.science.org/doi/10.1126/science.1110335)
+
+        [stackexchange answer, Gidney](https://quantumcomputing.stackexchange.com/a/23712)
+    """
+
+    bitsize: 'SymbolicInt'
+    is_adjoint: bool = False
+
+    @cached_property
+    def signature(self) -> 'Signature':
+        return Signature([Register('q', QUInt(self.bitsize), side=Side.LEFT)])
+
+    def build_call_graph(self, ssa: SympySymbolAllocator) -> 'BloqCountDictT':
+        t = ssa.new_symbol('t')
+        return {Hadamard(): self.bitsize, Measure(): self.bitsize, Rz(t): self.bitsize - 1}
+
+
+@bloq_example
+def _semi_classical_qft() -> SemiClassicalQFT:
+    semi_classical_qft = SemiClassicalQFT(3)
+    return semi_classical_qft
+
+
+_SEMI_CLASSICAL_QFT_DOC = BloqDocSpec(bloq_cls=SemiClassicalQFT, examples=(_semi_classical_qft,))

qualtran/bloqs/qft/semi_classical_qft_test.py

@@ -0,0 +1,28 @@
+#  Copyright 2025 Google LLC
+#
+#  Licensed under the Apache License, Version 2.0 (the "License");
+#  you may not use this file except in compliance with the License.
+#  You may obtain a copy of the License at
+#
+#      https://www.apache.org/licenses/LICENSE-2.0
+#
+#  Unless required by applicable law or agreed to in writing, software
+#  distributed under the License is distributed on an "AS IS" BASIS,
+#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#  See the License for the specific language governing permissions and
+#  limitations under the License.
+
+import pytest
+import sympy
+
+from qualtran.bloqs.qft import semi_classical_qft
+from qualtran.resource_counting import get_cost_value, QECGatesCost
+
+
+@pytest.mark.parametrize('n', [*range(1, 10), sympy.Symbol('n')])
+def test_semi_classical_qft_cost(n):
+    blq = semi_classical_qft.SemiClassicalQFT(n)
+    cost = get_cost_value(blq, QECGatesCost())
+    assert cost.rotation == n - 1
+    assert cost.clifford == n
+    assert cost.measurement == n

qualtran/serialization/resolver_dict.py

@@ -413,6 +413,7 @@
     "qualtran.bloqs.qft.approximate_qft.ApproximateQFT": qualtran.bloqs.qft.approximate_qft.ApproximateQFT,
     "qualtran.bloqs.qft.qft_phase_gradient.QFTPhaseGradient": qualtran.bloqs.qft.qft_phase_gradient.QFTPhaseGradient,
     "qualtran.bloqs.qft.qft_text_book.QFTTextBook": qualtran.bloqs.qft.qft_text_book.QFTTextBook,
+    "qualtran.bloqs.qft.semi_classical_qft.SemiClassicalQFT": qualtran.bloqs.qft.semi_classical_qft.SemiClassicalQFT,
     "qualtran.bloqs.qft.two_bit_ffft.TwoBitFFFT": qualtran.bloqs.qft.two_bit_ffft.TwoBitFFFT,
     "qualtran.bloqs.qsp.generalized_qsp.GeneralizedQSP": qualtran.bloqs.qsp.generalized_qsp.GeneralizedQSP,
     "qualtran.bloqs.qubitization.qubitization_walk_operator.QubitizationWalkOperator": qualtran.bloqs.qubitization.qubitization_walk_operator.QubitizationWalkOperator,