{
  "cells": [
    {
      "cell_type": "markdown",
      "id": "dd701ecc",
      "metadata": {},
      "source": [
        "---\n",
        "title: \"Ungefähre Quantenkompilierung für Zeitentwicklungsschaltungen\"\n",
        "description: \"Erfahren Sie, wie Sie mit AQC-Tensor Trotterisierte Zeitentwicklungsschaltungen komprimieren können, um eine effiziente Ausführung auf Quantenhardware zu ermöglichen.\"\n",
        "---\n",
        "\n",
        "{/* cspell:ignore circo Néel */}\n",
        "\n",
        "<span id=\"approximate-quantum-compilation-for-time-evolution-circuits\" />\n",
        "\n",
        "# Ungefähre Quantenkompilierung für Zeitentwicklungsschaltungen\n",
        "\n",
        "*Geschätzte Laufzeit: 15 Sekunden auf einem Heron-Prozessor (HINWEIS: Dies ist lediglich eine Schätzung. (Die Laufzeit kann variieren.)*\n",
        "\n"
      ]
    },
    {
      "cell_type": "markdown",
      "id": "12608301",
      "metadata": {},
      "source": [
        "<span id=\"learning-outcomes\" />\n",
        "\n",
        "## Lernziele\n",
        "\n",
        "* So verwenden Sie das AQC-Tensor-Qiskit-Add-on, um tiefe Trotter-Schaltungen in flache Ansatz-Schaltungen zu komprimieren\n",
        "* Wie man aus einem Trotter-Schaltkreis einen parametrisierten Ansatz generiert und dessen Parameter mithilfe von Tensornetzwerk-Methoden (MPS) optimiert\n",
        "* Wie man die Genauigkeit eines komprimierten Schaltkreises anhand der Sollentwicklung bewertet und ihn auf Quantenhardware ausführt\n",
        "\n"
      ]
    },
    {
      "cell_type": "markdown",
      "id": "c3c5992a",
      "metadata": {},
      "source": [
        "<span id=\"prerequisites\" />\n",
        "\n",
        "## Voraussetzungen\n",
        "\n",
        "* [Grundlagen von Quantenschaltungen](/learning/courses/basics-of-quantum-information)\n",
        "* [Hamilton-Simulation und Trotterisierung](/learning/courses/utility-scale-quantum-computing/quantum-simulation)\n",
        "* [Einführung in die Grundelemente](/docs/guides/primitives)\n",
        "\n"
      ]
    },
    {
      "cell_type": "markdown",
      "id": "714adc39",
      "metadata": {},
      "source": [
        "<span id=\"background\" />\n",
        "\n",
        "## Hintergrund\n",
        "\n",
        "Dieses Tutorial zeigt, wie man **die approximative Quantenkompilierung** unter Verwendung von Tensornetzwerken (AQC-Tensor) mit Qiskit implementiert, um die Leistung von Quantenschaltungen zu verbessern. AQC-Tensor komprimiert tiefe Trotter-Schaltkreise zu flacheren, hardwarefreundlicheren Schaltkreisen, wobei die Simulationsgenauigkeit erhalten bleibt.\n",
        "\n",
        "<span id=\"how-aqc-tensor-works\" />\n",
        "\n",
        "### So funktioniert AQC-Tensor\n",
        "\n",
        "Betrachten wir die Simulation eines Hamilton-Operators $H$ über die Gesamtzeit $t$ unter Verwendung von $k$ Trotter-Schritten. Der vollständige Trotter-Kreis lautet:\n",
        "\n",
        "$$\n",
        "U_{\\text{full}} = \\left[U_{\\text{Trotter}}(t/k)\\right]^k\n",
        "$$\n",
        "\n",
        "Bei einem naiven Ansatz werden nur wenige Trotter-Schritte verwendet, um die Schaltungstiefe überschaubar zu halten, was jedoch zu einem erheblichen Trotter-Fehler führt. AQC-Tensor löst diesen Konflikt, indem es Genauigkeit und Tiefe voneinander trennt:\n",
        "\n",
        "1. **Zielschaltung (hohe Genauigkeit, tief):** Konstruieren Sie eine Trotter-Schaltung mit vielen Schritten – beispielsweise $10k$ – für dieselbe Entwicklungszeit. Diese Schaltung weist einen weitaus geringeren Trotter-Fehler auf, ist jedoch für die Hardware zu komplex. Da dies klassisch lediglich als Matrixproduktzustand (MPS) simuliert wird, spielt die Tiefe keine Rolle.\n",
        "\n",
        "2. **Ansatz-Schaltung (geringe Tiefe, parametrisiert):** Definieren Sie eine parametrisierte Schaltung $V(\\theta)$ mit derselben Struktur wie eine Ein-Schritt-Trotter-Schaltung. Initialisiere es so, dass „ $V(\\theta_{\\text{init}}) = U_{\\text{Trotter}}(t/k)$ “, und optimiere dann iterativ „ $\\theta$ “, sodass „ $V(\\theta)$ “ den hochgenauen Zielzustand so genau wie möglich wiedergibt.\n",
        "\n",
        "Das Ergebnis ist eine Schaltung, die die Tiefe eines einzelnen Trotter-Schritts beibehält, aber die Genauigkeit vieler Schritte erreicht, wodurch sie für Quantencomputer der nahen Zukunft realisierbar wird.\n",
        "\n",
        "<span id=\"when-to-use-aqc-tensor\" />\n",
        "\n",
        "### Wann sollte man AQC-Tensor verwenden?\n",
        "\n",
        "AQC-Tensor ist am effektivsten, wenn:\n",
        "\n",
        "* **Die Schaltungstiefe übersteigt die Kohärenzzeiten der Hardware.** Wenn eine Trotter-Simulation mehr Trotter-Schritte erfordert, als das Gerät unterstützen kann, kann AQC-Tensor die Entwicklung in eine flachere Schaltung komprimieren.\n",
        "* **Verschränkung bleibt klassisch berechenbar.** Die Gesamtverschränkung in einem zeitlich entwickelten Zustand hängt in erster Linie von der Entwicklungszeit $t$ ab, nicht von der Anzahl der Trotter-Schritte $k$. Das bedeutet, dass eine Zielschaltung mit $10k$ Schritten in der Regel nicht schwieriger als MPS darzustellen ist als eine mit $k$ Schritten, solange $t$ kurz genug ist, damit die Bindungsabstände überschaubar bleiben.\n",
        "* **Es gibt einen natürlichen Ansatz.** Da der Ansatz die Struktur eines Trotter-Kreises widerspiegelt, bietet er einen physikalisch begründeten Ausgangspunkt mit genau definierten Anfangsparametern und vermeidet so die Konvergenzprobleme, die bei beliebigen Variationsansätzen auftreten können.\n",
        "\n",
        "Dieser Ansatz unterscheidet sich von der generischen Schaltungskompression: Anstatt zu versuchen, eine beliebige Unitarität mit weniger Gatter zu approximieren, behält AQC-Tensor die gleiche Gatterstruktur bei und optimiert deren Parameter, um den Trotter-Fehler zu reduzieren. Weitere Informationen finden Sie in der [AQC-Tensor-Dokumentation](https://qiskit.github.io/qiskit-addon-aqc-tensor/).\n",
        "\n",
        "Dieses Tutorial führt Sie durch den gesamten AQC-Tensor-Workflow zur Zustandsvorbereitung: Definition eines Hamilton-Operators, Erzeugung von Trotter-Schaltkreisen, deren Komprimierung mittels Tensor-Netzwerk-Optimierung und Ausführung des Ergebnisses auf der Hardware „ IBM Quantum® “.\n",
        "\n"
      ]
    },
    {
      "cell_type": "markdown",
      "id": "f8a05291",
      "metadata": {},
      "source": [
        "<span id=\"requirements\" />\n",
        "\n",
        "## Anforderungen\n",
        "\n",
        "Vergewissern Sie sich vor Beginn dieses Tutorials, dass Sie die folgenden Komponenten installiert haben:\n",
        "\n",
        "* Qiskit SDK v2.0 oder höher, mit [Visualisierungsunterstützung](/docs/api/qiskit/visualization)\n",
        "* Qiskit Runtime v0.22 oder später (`pip install qiskit-ibm-runtime`)\n",
        "* AQC-Tensor Qiskit-Erweiterung (`pip install 'qiskit-addon-aqc-tensor[aer,quimb-jax]'`)\n",
        "\n"
      ]
    },
    {
      "cell_type": "markdown",
      "id": "f9410d21",
      "metadata": {},
      "source": [
        "<span id=\"setup\" />\n",
        "\n",
        "## Einrichtung\n",
        "\n"
      ]
    },
    {
      "cell_type": "code",
      "execution_count": 1,
      "id": "ecdb92e0",
      "metadata": {},
      "outputs": [],
      "source": [
        "import numpy as np\n",
        "import quimb.tensor\n",
        "import datetime\n",
        "import matplotlib.pyplot as plt\n",
        "\n",
        "from scipy.linalg import expm\n",
        "from scipy.optimize import OptimizeResult, minimize\n",
        "\n",
        "from qiskit.quantum_info import SparsePauliOp, Pauli\n",
        "from qiskit.transpiler import CouplingMap\n",
        "from qiskit.transpiler.preset_passmanagers import generate_preset_pass_manager\n",
        "from qiskit import QuantumCircuit\n",
        "from qiskit.synthesis import SuzukiTrotter\n",
        "\n",
        "from qiskit_addon_utils.problem_generators import (\n",
        "    generate_time_evolution_circuit,\n",
        ")\n",
        "from qiskit_addon_aqc_tensor.ansatz_generation import (\n",
        "    generate_ansatz_from_circuit,\n",
        ")\n",
        "from qiskit_addon_aqc_tensor.objective import MaximizeStateFidelity\n",
        "from qiskit_addon_aqc_tensor.simulation.quimb import QuimbSimulator\n",
        "from qiskit_addon_aqc_tensor.simulation import tensornetwork_from_circuit\n",
        "from qiskit_addon_aqc_tensor.simulation import compute_overlap\n",
        "\n",
        "from qiskit_ibm_runtime import QiskitRuntimeService\n",
        "from qiskit_ibm_runtime import EstimatorV2 as Estimator\n",
        "from qiskit_ibm_runtime.fake_provider import FakeKyiv\n",
        "\n",
        "from rustworkx.visualization import graphviz_draw"
      ]
    },
    {
      "cell_type": "markdown",
      "id": "6473f943",
      "metadata": {},
      "source": [
        "<span id=\"small-scale-simulator-example\" />\n",
        "\n",
        "## Beispiel für einen Simulator im kleinen Maßstab\n",
        "\n",
        "In diesem Abschnitt wird der AQC-Tensor-Workflow anhand eines Systems mit 10 Standorten Schritt für Schritt veranschaulicht. Wir simulieren die Dynamik einer XXZ-Spinkette mit 10 Gitterpunkten, einem vielfach untersuchten Modell zur Untersuchung von Spinwechselwirkungen und magnetischen Eigenschaften.\n",
        "\n",
        "Der Hamilton-Operator lautet wie folgt:\n",
        "\n",
        "$$\n",
        "\\hat{\\mathcal{H}}_{XXZ} = \\sum_{i=1}^{L-1} J_{i,(i+1)}\\left(X_i X_{(i+1)}+Y_i Y_{(i+1)}+ 2\\cdot Z_i Z_{(i+1)} \\right) \\, ,\n",
        "$$\n",
        "\n",
        "wobei $J_{i,(i+1)}$ ein Zufallskoeffizient für die Kanten $(i, i+1)$ und $L=10$ ist.\n",
        "\n"
      ]
    },
    {
      "cell_type": "markdown",
      "id": "6520161e",
      "metadata": {},
      "source": [
        "<span id=\"step-1-map-classical-inputs-to-a-quantum-problem\" />\n",
        "\n",
        "### Schritt 1: Klassische Eingaben einem Quantenproblem zuordnen\n",
        "\n",
        "In diesem Schritt:\n",
        "\n",
        "1. Definieren Sie den Hamilton-Operator, die Observable und den Anfangszustand.\n",
        "2. Berechnen Sie den genauen Erwartungswert auf klassische Weise, um ihn später vergleichen zu können.\n",
        "3. Erstellen Sie eine hochgenaue Trotter-Schaltung (das AQC-Ziel) und komprimieren Sie diese mithilfe von AQC-Tensor zu einem Ansatz mit geringer Tiefe.\n",
        "\n"
      ]
    },
    {
      "cell_type": "markdown",
      "id": "bbeb5729",
      "metadata": {},
      "source": [
        "<span id=\"set-up-the-hamiltonian-observable-and-initial-state\" />\n",
        "\n",
        "#### Bestimme den Hamilton-Operator, die Observable und den Anfangszustand\n",
        "\n"
      ]
    },
    {
      "cell_type": "code",
      "execution_count": 2,
      "id": "527dbada",
      "metadata": {},
      "outputs": [
        {
          "name": "stdout",
          "output_type": "stream",
          "text": [
            "Hamiltonian: SparsePauliOp(['IIIIIIIIII', 'IIIIIIIIXX', 'IIIIIIIIYY', 'IIIIIIIIZZ', 'IIIIIIXXII', 'IIIIIIYYII', 'IIIIIIZZII', 'IIIIXXIIII', 'IIIIYYIIII', 'IIIIZZIIII', 'IIXXIIIIII', 'IIYYIIIIII', 'IIZZIIIIII', 'XXIIIIIIII', 'YYIIIIIIII', 'ZZIIIIIIII', 'IIIIIIIXXI', 'IIIIIIIYYI', 'IIIIIIIZZI', 'IIIIIXXIII', 'IIIIIYYIII', 'IIIIIZZIII', 'IIIXXIIIII', 'IIIYYIIIII', 'IIIZZIIIII', 'IXXIIIIIII', 'IYYIIIIIII', 'IZZIIIIIII'],\n",
            "              coeffs=[1.        +0.j, 0.52440675+0.j, 0.52440675+0.j, 1.0488135 +0.j,\n",
            " 0.60759468+0.j, 0.60759468+0.j, 1.21518937+0.j, 0.55138169+0.j,\n",
            " 0.55138169+0.j, 1.10276338+0.j, 0.52244159+0.j, 0.52244159+0.j,\n",
            " 1.04488318+0.j, 0.4618274 +0.j, 0.4618274 +0.j, 0.9236548 +0.j,\n",
            " 0.57294706+0.j, 0.57294706+0.j, 1.14589411+0.j, 0.46879361+0.j,\n",
            " 0.46879361+0.j, 0.93758721+0.j, 0.6958865 +0.j, 0.6958865 +0.j,\n",
            " 1.391773  +0.j, 0.73183138+0.j, 0.73183138+0.j, 1.46366276+0.j])\n",
            "Observable: SparsePauliOp(['IIIIZZIIII'],\n",
            "              coeffs=[1.+0.j])\n"
          ]
        },
        {
          "data": {
            "text/plain": [
              "<Image src=\"/docs/images/tutorials/approximate-quantum-compilation-for-time-evolution/extracted-outputs/527dbada-1.avif\" alt=\"Output of the previous code cell\" />"
            ]
          },
          "execution_count": 2,
          "metadata": {},
          "output_type": "execute_result"
        }
      ],
      "source": [
        "# L is the number of sites in the 1D spin chain\n",
        "L = 10\n",
        "\n",
        "# Generate the coupling map\n",
        "edge_list = [(i - 1, i) for i in range(1, L)]\n",
        "even_edges = edge_list[::2]\n",
        "odd_edges = edge_list[1::2]\n",
        "coupling_map = CouplingMap(edge_list)\n",
        "\n",
        "# Generate random coefficients for our XXZ Hamiltonian\n",
        "np.random.seed(0)\n",
        "Js = np.random.rand(L - 1) + 0.5 * np.ones(L - 1)\n",
        "hamiltonian = SparsePauliOp(Pauli(\"I\" * L))\n",
        "for i, edge in enumerate(even_edges + odd_edges):\n",
        "    hamiltonian += SparsePauliOp.from_sparse_list(\n",
        "        [\n",
        "            (\"XX\", (edge), Js[i] / 2),\n",
        "            (\"YY\", (edge), Js[i] / 2),\n",
        "            (\"ZZ\", (edge), Js[i]),\n",
        "        ],\n",
        "        num_qubits=L,\n",
        "    )\n",
        "\n",
        "# Generate a ZZ observable between the two middle qubits\n",
        "observable = SparsePauliOp.from_sparse_list(\n",
        "    [(\"ZZ\", (L // 2 - 1, L // 2), 1.0)], num_qubits=L\n",
        ")\n",
        "\n",
        "# Generate an initial Néel state |1010101010⟩\n",
        "initial_state_circuit = QuantumCircuit(L)\n",
        "for i in range(L):\n",
        "    if i % 2:\n",
        "        initial_state_circuit.x(i)\n",
        "\n",
        "print(\"Hamiltonian:\", hamiltonian)\n",
        "print(\"Observable:\", observable)\n",
        "graphviz_draw(coupling_map.graph, method=\"circo\")"
      ]
    },
    {
      "cell_type": "markdown",
      "id": "54ad6963",
      "metadata": {},
      "source": [
        "<span id=\"compute-the-exact-expectation-value\" />\n",
        "\n",
        "#### Berechne den genauen Erwartungswert\n",
        "\n",
        "Bei einem System dieser Größenordnung können wir den exakten zeitabhängigen Erwartungswert direkt mittels Matrixexponentiation berechnen. Dies dient uns als Referenzwert für die Bewertung der Genauigkeit der AQC-Schaltung.\n",
        "\n"
      ]
    },
    {
      "cell_type": "code",
      "execution_count": 3,
      "id": "20c70651",
      "metadata": {},
      "outputs": [
        {
          "name": "stdout",
          "output_type": "stream",
          "text": [
            "AQC evolution time: 0.2\n",
            "Subsequent evolution time: 0.066667\n",
            "Total evolution time: 0.266667\n",
            "Exact expectation value: -0.700899\n"
          ]
        }
      ],
      "source": [
        "aqc_evolution_time = 0.2\n",
        "\n",
        "# Each baseline Trotter step covers dt = aqc_evolution_time / 3\n",
        "# The subsequent (uncompressed) step covers 1 additional dt\n",
        "subsequent_evolution_time = aqc_evolution_time / 3\n",
        "total_evolution_time = aqc_evolution_time + subsequent_evolution_time\n",
        "\n",
        "# Compute exact expectation value via matrix exponentiation\n",
        "H_matrix = hamiltonian.to_matrix()\n",
        "U_exact = expm(-1j * H_matrix * total_evolution_time)\n",
        "\n",
        "# Build the initial state vector (Néel state)\n",
        "initial_state_vec = np.zeros(2**L)\n",
        "state_idx = sum(2**i for i in range(L) if i % 2)\n",
        "initial_state_vec[state_idx] = 1.0\n",
        "\n",
        "# Evolve and compute expectation value\n",
        "evolved_state = U_exact @ initial_state_vec\n",
        "obs_matrix = observable.to_matrix()\n",
        "exact_expval = (evolved_state.conj() @ obs_matrix @ evolved_state).real\n",
        "\n",
        "print(f\"AQC evolution time: {aqc_evolution_time}\")\n",
        "print(f\"Subsequent evolution time: {subsequent_evolution_time:.6f}\")\n",
        "print(f\"Total evolution time: {total_evolution_time:.6f}\")\n",
        "print(f\"Exact expectation value: {exact_expval:.6f}\")"
      ]
    },
    {
      "cell_type": "markdown",
      "id": "a93c047c",
      "metadata": {},
      "source": [
        "<span id=\"generate-the-aqc-target-circuit\" />\n",
        "\n",
        "#### Erstellen Sie die AQC-Zielschaltung\n",
        "\n",
        "Wir konstruieren nun den Trotter-Schaltkreis, der als Ziel für den AQC dienen soll. Diese Schaltung nutzt zahlreiche Trotter-Stufen (32), um eine hohe Genauigkeit zu gewährleisten. Da dies lediglich klassisch als MPS simuliert – und nicht auf Hardware ausgeführt – wird, stellt die große Tiefe kein Problem dar.\n",
        "\n"
      ]
    },
    {
      "cell_type": "code",
      "execution_count": 4,
      "id": "db66bf00",
      "metadata": {},
      "outputs": [],
      "source": [
        "aqc_target_num_trotter_steps = 32\n",
        "\n",
        "aqc_target_circuit = initial_state_circuit.copy()\n",
        "aqc_target_circuit.compose(\n",
        "    generate_time_evolution_circuit(\n",
        "        hamiltonian,\n",
        "        synthesis=SuzukiTrotter(reps=aqc_target_num_trotter_steps),\n",
        "        time=aqc_evolution_time,\n",
        "    ),\n",
        "    inplace=True,\n",
        ")"
      ]
    },
    {
      "cell_type": "markdown",
      "id": "bce1ef52",
      "metadata": {},
      "source": [
        "<span id=\"generate-an-ansatz-initial-parameters-subsequent-circuit-and-a-baseline-circuit\" />\n",
        "\n",
        "#### Erstellen Sie einen Ansatz, Anfangsparameter, einen Folgekreis und einen Referenzkreis\n",
        "\n",
        "Als Nächstes konstruieren wir eine „gute“ Schaltung mit derselben Evolutionszeit wie das AQC-Ziel, jedoch mit weitaus weniger Trotter-Schritten (nur einem). Wir übergeben diese Funktion an `generate_ansatz_from_circuit`, die Folgendes zurückgibt:\n",
        "\n",
        "1. Eine allgemeine, parametrisierte **Ansatz** schaltung mit derselben Zwei-Qubit-Verbindung.\n",
        "2. **Ausgangsparameter,** die die Eingangsschaltung nachbilden, wenn sie in den Ansatz eingefügt werden.\n",
        "\n",
        "Außerdem konstruieren wir:\n",
        "\n",
        "* Eine **nachfolgende Schaltung** mit einem Trotter-Schritt, die (unkomprimiert) an den AQC-optimierten Teil angehängt wird, entsprechend dem Ansatz im [Tutorial](https://qiskit.github.io/qiskit-addon-aqc-tensor/tutorials/01_initial_state_aqc.html) zum AQC-Tensor-Ausgangszustand.\n",
        "* Ein **Basis-Trotter-Schaltkreis,** der vier Trotter-Schritte über die gesamte Laufzeit hinweg verwendet (`aqc_evolution_time + subsequent_evolution_time`). Dies dient als Vergleichsgrundlage: Er entspricht dem, was man auf Hardware ohne AQC ausführen würde. Der AQC-Ansatz (3 komprimierte Schritte + 1 unkomprimierter Schritt) erzielt bei geringerer Tiefe eine höhere Genauigkeit.\n",
        "\n"
      ]
    },
    {
      "cell_type": "code",
      "execution_count": null,
      "id": "78f2665e",
      "metadata": {},
      "outputs": [
        {
          "name": "stdout",
          "output_type": "stream",
          "text": [
            "Target circuit:      depth 384\n",
            "Baseline circuit:    depth 48 (4 Trotter steps, time=0.2667)\n",
            "Subsequent circuit:  depth 12 (1 Trotter step, time=0.0667)\n",
            "Ansatz circuit:      depth 3, with 156 parameters\n"
          ]
        },
        {
          "data": {
            "text/plain": [
              "<Image src=\"/docs/images/tutorials/approximate-quantum-compilation-for-time-evolution/extracted-outputs/78f2665e-1.avif\" alt=\"Output of the previous code cell\" />"
            ]
          },
          "execution_count": 5,
          "metadata": {},
          "output_type": "execute_result"
        }
      ],
      "source": [
        "aqc_ansatz_num_trotter_steps = 1\n",
        "\n",
        "aqc_good_circuit = initial_state_circuit.copy()\n",
        "aqc_good_circuit.compose(\n",
        "    generate_time_evolution_circuit(\n",
        "        hamiltonian,\n",
        "        synthesis=SuzukiTrotter(reps=aqc_ansatz_num_trotter_steps),\n",
        "        time=aqc_evolution_time,\n",
        "    ),\n",
        "    inplace=True,\n",
        ")\n",
        "\n",
        "aqc_ansatz, aqc_initial_parameters = generate_ansatz_from_circuit(\n",
        "    aqc_good_circuit\n",
        ")\n",
        "\n",
        "# Subsequent circuit: 1 non-compressed Trotter step appended after AQC\n",
        "subsequent_num_trotter_steps = 1\n",
        "subsequent_circuit = generate_time_evolution_circuit(\n",
        "    hamiltonian,\n",
        "    synthesis=SuzukiTrotter(reps=subsequent_num_trotter_steps),\n",
        "    time=subsequent_evolution_time,\n",
        ")\n",
        "\n",
        "# Baseline Trotter circuit: 4 Trotter steps over total evolution time, no AQC\n",
        "baseline_num_trotter_steps = 4\n",
        "baseline_circuit = initial_state_circuit.copy()\n",
        "baseline_circuit.compose(\n",
        "    generate_time_evolution_circuit(\n",
        "        hamiltonian,\n",
        "        synthesis=SuzukiTrotter(reps=baseline_num_trotter_steps),\n",
        "        time=total_evolution_time,\n",
        "    ),\n",
        "    inplace=True,\n",
        ")\n",
        "\n",
        "print(\n",
        "    f\"Target circuit:      depth {aqc_target_circuit.depth(lambda x: x.operation.num_qubits == 2)}\"\n",
        ")\n",
        "print(\n",
        "    f\"Baseline circuit:    depth {baseline_circuit.depth(lambda x: x.operation.num_qubits == 2)} ({baseline_num_trotter_steps} Trotter steps, time={total_evolution_time:.4f})\"\n",
        ")\n",
        "print(\n",
        "    f\"Subsequent circuit:  depth {subsequent_circuit.depth(lambda x: x.operation.num_qubits == 2)} ({subsequent_num_trotter_steps} Trotter step, time={subsequent_evolution_time:.4f})\"\n",
        ")\n",
        "print(\n",
        "    f\"Ansatz circuit:      depth {aqc_ansatz.depth(lambda x: x.operation.num_qubits == 2)}, with {len(aqc_initial_parameters)} parameters\"\n",
        ")\n",
        "aqc_ansatz.draw(\"mpl\", fold=-1)"
      ]
    },
    {
      "cell_type": "markdown",
      "id": "be1b4049",
      "metadata": {},
      "source": [
        "<span id=\"set-up-tensor-network-simulation-and-build-the-target-mps\" />\n",
        "\n",
        "#### Richten Sie eine Tensor-Network-Simulation ein und erstellen Sie das gewünschte MPS\n",
        "\n",
        "Wir verwenden den Matrix-Product-State-Schaltkreissimulator (MPS) [„quimb“](https://github.com/jcmgray/quimb), wobei JAX die automatische Differenzierung für die gradientbasierte Optimierung übernimmt. Anschließend erstellen wir eine MPS-Darstellung des Zielzustands und berechnen die anfängliche Übereinstimmung zwischen dem Ausgangsansatz und dem Ziel. Da es sich bei der Probleminstanz um ein relativ kleines Beispiel handelt, ist die anfängliche Genauigkeit recht hoch.\n",
        "\n"
      ]
    },
    {
      "cell_type": "code",
      "execution_count": 6,
      "id": "666fcf42",
      "metadata": {},
      "outputs": [
        {
          "name": "stdout",
          "output_type": "stream",
          "text": [
            "Target MPS maximum bond dimension: 5\n",
            "Starting fidelity: 0.998246\n"
          ]
        }
      ],
      "source": [
        "simulator_settings = QuimbSimulator(\n",
        "    quimb.tensor.CircuitMPS, autodiff_backend=\"jax\"\n",
        ")\n",
        "\n",
        "aqc_target_mps = tensornetwork_from_circuit(\n",
        "    aqc_target_circuit, simulator_settings\n",
        ")\n",
        "print(\"Target MPS maximum bond dimension:\", aqc_target_mps.psi.max_bond())\n",
        "\n",
        "good_mps = tensornetwork_from_circuit(aqc_good_circuit, simulator_settings)\n",
        "starting_fidelity = abs(compute_overlap(good_mps, aqc_target_mps)) ** 2\n",
        "print(f\"Starting fidelity: {starting_fidelity:.6f}\")"
      ]
    },
    {
      "cell_type": "markdown",
      "id": "1f14eb3f",
      "metadata": {},
      "source": [
        "<span id=\"optimize-the-ansatz-parameters\" />\n",
        "\n",
        "#### Die Ansatzparameter optimieren\n",
        "\n",
        "Wir minimieren die `MaximizeStateFidelity` Kostenfunktion mit Hilfe des L-BFGS-B-Optimierers. Der Optimierer passt die Ansatzparameter iterativ an, um die Übereinstimmung zwischen der Ansatzschaltung und dem Ziel-MPS zu maximieren.\n",
        "\n"
      ]
    },
    {
      "cell_type": "code",
      "execution_count": 7,
      "id": "6ad144d6",
      "metadata": {},
      "outputs": [
        {
          "name": "stdout",
          "output_type": "stream",
          "text": [
            "2026-05-18 13:14:49.731596 Intermediate result: Fidelity 0.99952882\n",
            "2026-05-18 13:14:49.734425 Intermediate result: Fidelity 0.99958531\n",
            "2026-05-18 13:14:49.737101 Intermediate result: Fidelity 0.99960093\n",
            "2026-05-18 13:14:49.739813 Intermediate result: Fidelity 0.99961046\n",
            "2026-05-18 13:14:49.742969 Intermediate result: Fidelity 0.99962560\n",
            "2026-05-18 13:14:49.745916 Intermediate result: Fidelity 0.99964395\n",
            "2026-05-18 13:14:49.748615 Intermediate result: Fidelity 0.99968150\n",
            "2026-05-18 13:14:49.753684 Intermediate result: Fidelity 0.99970569\n",
            "2026-05-18 13:14:49.756208 Intermediate result: Fidelity 0.99973788\n",
            "2026-05-18 13:14:49.759067 Intermediate result: Fidelity 0.99975385\n",
            "2026-05-18 13:14:49.762321 Intermediate result: Fidelity 0.99976458\n",
            "2026-05-18 13:14:49.765526 Intermediate result: Fidelity 0.99977661\n",
            "2026-05-18 13:14:49.768496 Intermediate result: Fidelity 0.99978663\n",
            "2026-05-18 13:14:49.771278 Intermediate result: Fidelity 0.99980236\n",
            "2026-05-18 13:14:49.773735 Intermediate result: Fidelity 0.99981607\n",
            "2026-05-18 13:14:49.776339 Intermediate result: Fidelity 0.99982811\n",
            "2026-05-18 13:14:49.779177 Intermediate result: Fidelity 0.99985827\n",
            "2026-05-18 13:14:49.782243 Intermediate result: Fidelity 0.99988354\n",
            "2026-05-18 13:14:49.784904 Intermediate result: Fidelity 0.99991608\n",
            "2026-05-18 13:14:49.787737 Intermediate result: Fidelity 0.99993336\n",
            "2026-05-18 13:14:49.790414 Intermediate result: Fidelity 0.99993956\n",
            "2026-05-18 13:14:49.793029 Intermediate result: Fidelity 0.99994421\n",
            "2026-05-18 13:14:49.795585 Intermediate result: Fidelity 0.99994743\n",
            "2026-05-18 13:14:49.835045 Intermediate result: Fidelity 0.99994791\n",
            "2026-05-18 13:14:49.839786 Intermediate result: Fidelity 0.99994803\n",
            "2026-05-18 13:14:49.842403 Intermediate result: Fidelity 0.99994898\n",
            "2026-05-18 13:14:49.873779 Intermediate result: Fidelity 0.99994898\n",
            "Done after 27 iterations.\n"
          ]
        }
      ],
      "source": [
        "aqc_stopping_fidelity = 1\n",
        "aqc_max_iterations = 500\n",
        "\n",
        "stopping_point = 1.0 - aqc_stopping_fidelity\n",
        "objective = MaximizeStateFidelity(\n",
        "    aqc_target_mps, aqc_ansatz, simulator_settings\n",
        ")\n",
        "\n",
        "\n",
        "def callback(intermediate_result: OptimizeResult):\n",
        "    fidelity = 1 - intermediate_result.fun\n",
        "    print(\n",
        "        f\"{datetime.datetime.now()} Intermediate result: Fidelity {fidelity:.8f}\"\n",
        "    )\n",
        "    if intermediate_result.fun < stopping_point:\n",
        "        raise StopIteration\n",
        "\n",
        "\n",
        "result = minimize(\n",
        "    objective,\n",
        "    aqc_initial_parameters,\n",
        "    method=\"L-BFGS-B\",\n",
        "    jac=True,\n",
        "    options={\"maxiter\": aqc_max_iterations},\n",
        "    callback=callback,\n",
        ")\n",
        "if result.status not in (0, 1, 99):\n",
        "    raise RuntimeError(\n",
        "        f\"Optimization failed: {result.message} (status={result.status})\"\n",
        "    )\n",
        "\n",
        "print(f\"Done after {result.nit} iterations.\")\n",
        "aqc_final_parameters = result.x"
      ]
    },
    {
      "cell_type": "markdown",
      "id": "ea5b484a",
      "metadata": {},
      "source": [
        "<span id=\"assemble-the-final-aqc-circuit\" />\n",
        "\n",
        "#### Die endgültige AQC-Schaltung zusammenbauen\n",
        "\n",
        "Nachdem wir die optimierten Parameter ermittelt haben, setzen wir sie in den Ansatz ein und fügen anschließend den (unkomprimierten) Trotter-Schritt hinzu. Die resultierende Schaltung hat die Tiefe eines einzelnen komprimierten Trotter-Schritts plus eines unkomprimierten Schritts, doch der komprimierte Teil erreicht eine Genauigkeit, die der von 32 Trotter-Schritten nahekommt.\n",
        "\n"
      ]
    },
    {
      "cell_type": "code",
      "execution_count": 8,
      "id": "e09e40de",
      "metadata": {},
      "outputs": [
        {
          "data": {
            "text/plain": [
              "<Image src=\"/docs/images/tutorials/approximate-quantum-compilation-for-time-evolution/extracted-outputs/e09e40de-0.avif\" alt=\"Output of the previous code cell\" />"
            ]
          },
          "execution_count": 8,
          "metadata": {},
          "output_type": "execute_result"
        }
      ],
      "source": [
        "aqc_final_circuit = aqc_ansatz.assign_parameters(aqc_final_parameters)\n",
        "aqc_final_circuit.compose(subsequent_circuit, inplace=True)\n",
        "aqc_final_circuit.draw(\"mpl\", fold=-1)"
      ]
    },
    {
      "cell_type": "markdown",
      "id": "047511db",
      "metadata": {},
      "source": [
        "<span id=\"step-2-optimize-problem-for-quantum-hardware-execution\" />\n",
        "\n",
        "### Schritt 2: Optimierung des Problems für die Ausführung auf Quantenhardware\n",
        "\n",
        "Für dieses kleine Beispiel verwenden wir ein simuliertes Backend (`FakeKyiv`), um die Hardwareausführung lokal zu simulieren. Wir transpilieren sowohl die AQC-optimierte Schaltung (`aqc_final_circuit`) als auch die Basis-Trotter-Schaltung (`baseline_circuit`, vier Trotter-Schritte über die gesamte Laufzeit, ohne AQC) in die Befehlssatzarchitektur (ISA) des Backends, wobei `optimization_level=3` verwendet wird, um die Schaltungstiefe weiter zu reduzieren.\n",
        "\n"
      ]
    },
    {
      "cell_type": "code",
      "execution_count": 9,
      "id": "9e7556dd",
      "metadata": {},
      "outputs": [
        {
          "name": "stdout",
          "output_type": "stream",
          "text": [
            "AQC circuit depth: 15\n",
            "Baseline Trotter circuit depth: 27\n"
          ]
        }
      ],
      "source": [
        "backend = FakeKyiv()\n",
        "\n",
        "pass_manager = generate_preset_pass_manager(\n",
        "    backend=backend, optimization_level=3\n",
        ")\n",
        "\n",
        "# Transpile the AQC-optimized circuit (compressed + subsequent step)\n",
        "isa_circuit = pass_manager.run(aqc_final_circuit)\n",
        "isa_observable = observable.apply_layout(isa_circuit.layout)\n",
        "print(\n",
        "    \"AQC circuit depth:\",\n",
        "    isa_circuit.depth(lambda x: x.operation.num_qubits == 2),\n",
        ")\n",
        "\n",
        "# Transpile the baseline Trotter circuit (no AQC optimization)\n",
        "isa_baseline_circuit = pass_manager.run(baseline_circuit)\n",
        "isa_baseline_observable = observable.apply_layout(isa_baseline_circuit.layout)\n",
        "print(\n",
        "    \"Baseline Trotter circuit depth:\",\n",
        "    isa_baseline_circuit.depth(lambda x: x.operation.num_qubits == 2),\n",
        ")"
      ]
    },
    {
      "cell_type": "markdown",
      "id": "60aec566",
      "metadata": {},
      "source": [
        "<span id=\"step-3-execute-using-qiskit-primitives\" />\n",
        "\n",
        "### Schritt 3: Mit „ Qiskit primitives “ ausführen\n",
        "\n",
        "Wir verwenden die Primitive [`EstimatorV2`](/docs/api/qiskit-ibm-runtime/executor-estimator-estimator) mit dem simulierten Backend, um sowohl die AQC-optimierte Schaltung als auch die Basis-Trotter-Schaltung auszuführen, und messen dabei jeweils die ZZ-Beobachtungsgröße.\n",
        "\n"
      ]
    },
    {
      "cell_type": "code",
      "execution_count": 10,
      "id": "241e24f2",
      "metadata": {},
      "outputs": [],
      "source": [
        "estimator = Estimator(backend)\n",
        "\n",
        "# Run both circuits\n",
        "aqc_result = estimator.run([(isa_circuit, isa_observable)]).result()\n",
        "baseline_result = estimator.run(\n",
        "    [(isa_baseline_circuit, isa_baseline_observable)]\n",
        ").result()"
      ]
    },
    {
      "cell_type": "markdown",
      "id": "0b980055",
      "metadata": {},
      "source": [
        "<span id=\"step-4-post-process-and-return-result-in-desired-classical-format\" />\n",
        "\n",
        "### Schritt 4: Nachbearbeitung und Rückgabe des Ergebnisses im gewünschten klassischen Format\n",
        "\n",
        "Wir ermitteln die Erwartungswerte aus beiden Durchläufen und vergleichen sie mit dem exakten Ergebnis. Der Referenz-Trotter-Schaltkreis zeigt, was wir ohne AQC bei gleicher Schaltkreistiefe erhalten würden, während der AQC-Schaltkreis die Verbesserung durch die Tensor-Netzwerk-Optimierung verdeutlicht.\n",
        "\n"
      ]
    },
    {
      "cell_type": "code",
      "execution_count": 11,
      "id": "af07a1d9",
      "metadata": {},
      "outputs": [
        {
          "name": "stdout",
          "output_type": "stream",
          "text": [
            "Exact:              -0.7009\n",
            "Baseline Trotter:   -0.5400, |Δ| = 0.1609  (depth 27, 4 steps)\n",
            "AQC (3+1):          -0.5728, |Δ| = 0.1281  (depth 15, compressed+subsequent)\n"
          ]
        }
      ],
      "source": [
        "aqc_expval = aqc_result[0].data.evs.tolist()\n",
        "baseline_expval = baseline_result[0].data.evs.tolist()\n",
        "\n",
        "print(f\"Exact:              {exact_expval:.4f}\")\n",
        "print(\n",
        "    f\"Baseline Trotter:   {baseline_expval:.4f}, |\\u0394| = {np.abs(exact_expval - baseline_expval):.4f}  (depth {isa_baseline_circuit.depth(lambda x: x.operation.num_qubits == 2)}, {baseline_num_trotter_steps} steps)\"\n",
        ")\n",
        "print(\n",
        "    f\"AQC (3+1):          {aqc_expval:.4f}, |\\u0394| = {np.abs(exact_expval - aqc_expval):.4f}  (depth {isa_circuit.depth(lambda x: x.operation.num_qubits == 2)}, compressed+subsequent)\"\n",
        ")"
      ]
    },
    {
      "cell_type": "code",
      "execution_count": 12,
      "id": "77c39ba8",
      "metadata": {},
      "outputs": [
        {
          "data": {
            "text/plain": [
              "<Image src=\"/docs/images/tutorials/approximate-quantum-compilation-for-time-evolution/extracted-outputs/77c39ba8-0.avif\" alt=\"Output of the previous code cell\" />"
            ]
          },
          "metadata": {},
          "output_type": "display_data"
        }
      ],
      "source": [
        "plt.style.use(\"seaborn-v0_8\")\n",
        "\n",
        "labels = [\n",
        "    f\"Baseline Trotter\\n({baseline_num_trotter_steps} steps, depth {isa_baseline_circuit.depth(lambda x: x.operation.num_qubits == 2)})\",\n",
        "    f\"AQC (3+1)\\n(depth {isa_circuit.depth(lambda x: x.operation.num_qubits == 2)})\",\n",
        "]\n",
        "values = [baseline_expval, aqc_expval]\n",
        "colors = [\"tab:orange\", \"tab:blue\"]\n",
        "\n",
        "plt.figure(figsize=(8, 5))\n",
        "bars = plt.bar(labels, values, color=colors, width=0.5)\n",
        "plt.axhline(\n",
        "    y=exact_expval,\n",
        "    color=\"tab:green\",\n",
        "    linestyle=\"--\",\n",
        "    linewidth=2,\n",
        "    label=f\"Exact ({exact_expval:.4f})\",\n",
        ")\n",
        "plt.ylabel(\"Expected Value\")\n",
        "plt.title(\n",
        "    \"AQC-Tensor (3 compressed + 1 uncompressed) vs Baseline Trotter (10-site XXZ)\"\n",
        ")\n",
        "plt.legend()\n",
        "for bar in bars:\n",
        "    y_val = bar.get_height()\n",
        "    plt.text(\n",
        "        bar.get_x() + bar.get_width() / 2.0,\n",
        "        y_val,\n",
        "        f\"{y_val:.4f}\",\n",
        "        ha=\"center\",\n",
        "        va=\"bottom\" if y_val >= 0 else \"top\",\n",
        "    )\n",
        "plt.axhline(y=0, color=\"black\", linewidth=0.3)\n",
        "plt.tight_layout()\n",
        "plt.show()"
      ]
    },
    {
      "cell_type": "markdown",
      "id": "37062efa",
      "metadata": {},
      "source": [
        "<span id=\"large-scale-hardware-example\" />\n",
        "\n",
        "## Beispiel für groß angelegte Hardware\n",
        "\n",
        "Wir erweitern nun auf ein XXZ-Modell mit 50 Standorten, um AQC-Tensor an einem realistischeren Problemumfang zu demonstrieren. Der Ablauf ist derselbe wie im Beispiel für den kleinen Maßstab: Wir komprimieren drei Trotter-Schritte mittels AQC und fügen einen unkomprimierten Schritt an.\n",
        "\n",
        "Bei einem System dieser Größenordnung ist die Matrixpotenzierung nicht durchführbar (Dimensionen $2^{50}$ ), daher berechnen wir den Referenzerwartungswert direkt aus einem hochgenauen MPS, das über den gesamten Zeitraum entwickelt wurde.\n",
        "\n",
        "<span id=\"steps-1–4-combined\" />\n",
        "\n",
        "### Schritte 1–4 zusammengefasst\n",
        "\n"
      ]
    },
    {
      "cell_type": "code",
      "execution_count": 13,
      "id": "b6c0f26a",
      "metadata": {},
      "outputs": [
        {
          "name": "stdout",
          "output_type": "stream",
          "text": [
            "Target circuit:  depth 385\n",
            "Ansatz circuit:  depth 7, with 816 parameters\n",
            "Subsequent circuit: depth 12\n",
            "Baseline circuit:   depth 49 (4 steps, time=0.2667)\n",
            "Target MPS maximum bond dimension: 5\n",
            "Reference expectation value (from MPS): -0.738669\n",
            "2026-05-18 13:02:11.219150 Intermediate result: Fidelity 0.99795732\n",
            "2026-05-18 13:02:11.232256 Intermediate result: Fidelity 0.99822481\n",
            "2026-05-18 13:02:11.245160 Intermediate result: Fidelity 0.99829520\n",
            "2026-05-18 13:02:11.257765 Intermediate result: Fidelity 0.99832379\n",
            "2026-05-18 13:02:11.270280 Intermediate result: Fidelity 0.99836416\n",
            "2026-05-18 13:02:11.284116 Intermediate result: Fidelity 0.99840073\n",
            "2026-05-18 13:02:11.296856 Intermediate result: Fidelity 0.99846863\n",
            "2026-05-18 13:02:11.309602 Intermediate result: Fidelity 0.99865244\n",
            "2026-05-18 13:02:11.322012 Intermediate result: Fidelity 0.99872665\n",
            "2026-05-18 13:02:11.334195 Intermediate result: Fidelity 0.99892335\n",
            "2026-05-18 13:02:11.346570 Intermediate result: Fidelity 0.99901045\n",
            "2026-05-18 13:02:11.359202 Intermediate result: Fidelity 0.99907181\n",
            "2026-05-18 13:02:11.371511 Intermediate result: Fidelity 0.99911125\n",
            "2026-05-18 13:02:11.383870 Intermediate result: Fidelity 0.99918585\n",
            "2026-05-18 13:02:11.396184 Intermediate result: Fidelity 0.99921504\n",
            "2026-05-18 13:02:11.408543 Intermediate result: Fidelity 0.99924936\n",
            "2026-05-18 13:02:11.422557 Intermediate result: Fidelity 0.99929226\n",
            "2026-05-18 13:02:11.436275 Intermediate result: Fidelity 0.99933099\n",
            "2026-05-18 13:02:11.449511 Intermediate result: Fidelity 0.99935792\n",
            "2026-05-18 13:02:11.462093 Intermediate result: Fidelity 0.99937925\n",
            "2026-05-18 13:02:11.475783 Intermediate result: Fidelity 0.99940690\n",
            "2026-05-18 13:02:11.490254 Intermediate result: Fidelity 0.99944409\n",
            "2026-05-18 13:02:11.503292 Intermediate result: Fidelity 0.99946840\n",
            "2026-05-18 13:02:11.516064 Intermediate result: Fidelity 0.99949378\n",
            "2026-05-18 13:02:11.532861 Intermediate result: Fidelity 0.99951380\n",
            "2026-05-18 13:02:11.546182 Intermediate result: Fidelity 0.99955313\n",
            "2026-05-18 13:02:11.559168 Intermediate result: Fidelity 0.99955707\n",
            "2026-05-18 13:02:11.571753 Intermediate result: Fidelity 0.99959306\n",
            "2026-05-18 13:02:11.584257 Intermediate result: Fidelity 0.99960486\n",
            "2026-05-18 13:02:11.597610 Intermediate result: Fidelity 0.99961714\n",
            "2026-05-18 13:02:11.610106 Intermediate result: Fidelity 0.99962953\n",
            "2026-05-18 13:02:11.622515 Intermediate result: Fidelity 0.99963525\n",
            "2026-05-18 13:02:11.635543 Intermediate result: Fidelity 0.99964658\n",
            "2026-05-18 13:02:11.649044 Intermediate result: Fidelity 0.99965027\n",
            "2026-05-18 13:02:11.664148 Intermediate result: Fidelity 0.99965802\n",
            "2026-05-18 13:02:11.678033 Intermediate result: Fidelity 0.99966731\n",
            "2026-05-18 13:02:11.692714 Intermediate result: Fidelity 0.99967780\n",
            "2026-05-18 13:02:11.706753 Intermediate result: Fidelity 0.99968567\n",
            "2026-05-18 13:02:11.720780 Intermediate result: Fidelity 0.99969139\n",
            "2026-05-18 13:02:11.733471 Intermediate result: Fidelity 0.99969628\n",
            "2026-05-18 13:02:11.745998 Intermediate result: Fidelity 0.99970331\n",
            "2026-05-18 13:02:11.758424 Intermediate result: Fidelity 0.99970796\n",
            "2026-05-18 13:02:11.771986 Intermediate result: Fidelity 0.99971165\n",
            "2026-05-18 13:02:11.785841 Intermediate result: Fidelity 0.99971892\n",
            "2026-05-18 13:02:11.799105 Intermediate result: Fidelity 0.99972226\n",
            "2026-05-18 13:02:11.811623 Intermediate result: Fidelity 0.99972441\n",
            "2026-05-18 13:02:11.824114 Intermediate result: Fidelity 0.99972679\n",
            "2026-05-18 13:02:11.837179 Intermediate result: Fidelity 0.99972965\n",
            "2026-05-18 13:02:12.345479 Intermediate result: Fidelity 0.99972965\n",
            "Done after 49 iterations.\n",
            "<IBMBackend('ibm_pittsburgh')>\n",
            "AQC circuit depth: 71\n",
            "Baseline Trotter circuit depth: 111\n",
            "Job ID: d85kc6o0bvlc73d5nhn0\n"
          ]
        }
      ],
      "source": [
        "# -------------------------Step 1-------------------------\n",
        "\n",
        "# Define the 50-site spin chain\n",
        "L = 50\n",
        "edge_list = [(i - 1, i) for i in range(1, L)]\n",
        "even_edges = edge_list[::2]\n",
        "odd_edges = edge_list[1::2]\n",
        "coupling_map = CouplingMap(edge_list)\n",
        "\n",
        "# Random XXZ Hamiltonian\n",
        "np.random.seed(0)\n",
        "Js = np.random.rand(L - 1) + 0.5 * np.ones(L - 1)\n",
        "hamiltonian = SparsePauliOp(Pauli(\"I\" * L))\n",
        "for i, edge in enumerate(even_edges + odd_edges):\n",
        "    hamiltonian += SparsePauliOp.from_sparse_list(\n",
        "        [\n",
        "            (\"XX\", (edge), Js[i] / 2),\n",
        "            (\"YY\", (edge), Js[i] / 2),\n",
        "            (\"ZZ\", (edge), Js[i]),\n",
        "        ],\n",
        "        num_qubits=L,\n",
        "    )\n",
        "\n",
        "observable = SparsePauliOp.from_sparse_list(\n",
        "    [(\"ZZ\", (L // 2 - 1, L // 2), 1.0)], num_qubits=L\n",
        ")\n",
        "\n",
        "# Initial Néel state\n",
        "initial_state_circuit = QuantumCircuit(L)\n",
        "for i in range(L):\n",
        "    if i % 2:\n",
        "        initial_state_circuit.x(i)\n",
        "\n",
        "# Time parameters\n",
        "aqc_evolution_time = 0.2\n",
        "subsequent_evolution_time = aqc_evolution_time / 3\n",
        "total_evolution_time = aqc_evolution_time + subsequent_evolution_time\n",
        "\n",
        "# AQC target circuit (high-accuracy, 32 Trotter steps for AQC portion)\n",
        "aqc_target_num_trotter_steps = 32\n",
        "\n",
        "aqc_target_circuit = initial_state_circuit.copy()\n",
        "aqc_target_circuit.compose(\n",
        "    generate_time_evolution_circuit(\n",
        "        hamiltonian,\n",
        "        synthesis=SuzukiTrotter(reps=aqc_target_num_trotter_steps),\n",
        "        time=aqc_evolution_time,\n",
        "    ),\n",
        "    inplace=True,\n",
        ")\n",
        "\n",
        "# Generate ansatz from 1-step Trotter circuit\n",
        "aqc_good_circuit = initial_state_circuit.copy()\n",
        "aqc_good_circuit.compose(\n",
        "    generate_time_evolution_circuit(\n",
        "        hamiltonian,\n",
        "        synthesis=SuzukiTrotter(reps=1),\n",
        "        time=aqc_evolution_time,\n",
        "    ),\n",
        "    inplace=True,\n",
        ")\n",
        "\n",
        "aqc_ansatz, aqc_initial_parameters = generate_ansatz_from_circuit(\n",
        "    aqc_good_circuit\n",
        ")\n",
        "\n",
        "# Subsequent circuit: 1 non-compressed Trotter step\n",
        "subsequent_circuit = generate_time_evolution_circuit(\n",
        "    hamiltonian,\n",
        "    synthesis=SuzukiTrotter(reps=1),\n",
        "    time=subsequent_evolution_time,\n",
        ")\n",
        "\n",
        "# Baseline Trotter circuit: 4 Trotter steps over total evolution time, no AQC\n",
        "baseline_num_trotter_steps = 4\n",
        "baseline_circuit = initial_state_circuit.copy()\n",
        "baseline_circuit.compose(\n",
        "    generate_time_evolution_circuit(\n",
        "        hamiltonian,\n",
        "        synthesis=SuzukiTrotter(reps=baseline_num_trotter_steps),\n",
        "        time=total_evolution_time,\n",
        "    ),\n",
        "    inplace=True,\n",
        ")\n",
        "print(\n",
        "    f\"Target circuit:  depth {aqc_target_circuit.depth(lambda x: x.operation.num_qubits == 2)}\"\n",
        ")\n",
        "print(\n",
        "    f\"Ansatz circuit:  depth {aqc_ansatz.depth(lambda x: x.operation.num_qubits == 2)}, with {len(aqc_initial_parameters)} parameters\"\n",
        ")\n",
        "print(\n",
        "    f\"Subsequent circuit: depth {subsequent_circuit.depth(lambda x: x.operation.num_qubits == 2)}\"\n",
        ")\n",
        "print(\n",
        "    f\"Baseline circuit:   depth {baseline_circuit.depth(lambda x: x.operation.num_qubits == 2)} ({baseline_num_trotter_steps} steps, time={total_evolution_time:.4f})\"\n",
        ")\n",
        "\n",
        "# Build target MPS and compute reference expectation value\n",
        "simulator_settings = QuimbSimulator(\n",
        "    quimb.tensor.CircuitMPS, autodiff_backend=\"jax\"\n",
        ")\n",
        "aqc_target_mps = tensornetwork_from_circuit(\n",
        "    aqc_target_circuit, simulator_settings\n",
        ")\n",
        "print(\"Target MPS maximum bond dimension:\", aqc_target_mps.psi.max_bond())\n",
        "\n",
        "# For the reference expectation value, we need the full evolution (AQC + subsequent)\n",
        "# Build a high-accuracy full circuit for MPS reference\n",
        "full_target_circuit = initial_state_circuit.copy()\n",
        "full_target_circuit.compose(\n",
        "    generate_time_evolution_circuit(\n",
        "        hamiltonian,\n",
        "        synthesis=SuzukiTrotter(reps=aqc_target_num_trotter_steps),\n",
        "        time=total_evolution_time,\n",
        "    ),\n",
        "    inplace=True,\n",
        ")\n",
        "full_target_mps = tensornetwork_from_circuit(\n",
        "    full_target_circuit, simulator_settings\n",
        ")\n",
        "exact_expval = full_target_mps.local_expectation(\n",
        "    quimb.pauli(\"Z\") & quimb.pauli(\"Z\"), (L // 2 - 1, L // 2)\n",
        ").real.item()\n",
        "print(f\"Reference expectation value (from MPS): {exact_expval:.6f}\")\n",
        "\n",
        "# Optimize ansatz parameters\n",
        "objective = MaximizeStateFidelity(\n",
        "    aqc_target_mps, aqc_ansatz, simulator_settings\n",
        ")\n",
        "\n",
        "\n",
        "def callback(intermediate_result: OptimizeResult):\n",
        "    fidelity = 1 - intermediate_result.fun\n",
        "    print(\n",
        "        f\"{datetime.datetime.now()} Intermediate result: Fidelity {fidelity:.8f}\"\n",
        "    )\n",
        "\n",
        "\n",
        "result = minimize(\n",
        "    objective,\n",
        "    aqc_initial_parameters,\n",
        "    method=\"L-BFGS-B\",\n",
        "    jac=True,\n",
        "    options={\"maxiter\": 500},\n",
        "    callback=callback,\n",
        ")\n",
        "if result.status not in (0, 1, 99):\n",
        "    raise RuntimeError(\n",
        "        f\"Optimization failed: {result.message} (status={result.status})\"\n",
        "    )\n",
        "print(f\"Done after {result.nit} iterations.\")\n",
        "\n",
        "# Assemble the final AQC circuit: optimized ansatz + subsequent Trotter step\n",
        "aqc_final_circuit = aqc_ansatz.assign_parameters(result.x)\n",
        "aqc_final_circuit.compose(subsequent_circuit, inplace=True)\n",
        "\n",
        "# -------------------------Step 2-------------------------\n",
        "\n",
        "service = QiskitRuntimeService()\n",
        "backend = service.least_busy(min_num_qubits=127)\n",
        "print(backend)\n",
        "\n",
        "pass_manager = generate_preset_pass_manager(\n",
        "    backend=backend, optimization_level=3\n",
        ")\n",
        "isa_circuit = pass_manager.run(aqc_final_circuit)\n",
        "isa_observable = observable.apply_layout(isa_circuit.layout)\n",
        "print(\n",
        "    \"AQC circuit depth:\",\n",
        "    isa_circuit.depth(lambda x: x.operation.num_qubits == 2),\n",
        ")\n",
        "\n",
        "# Also transpile the baseline Trotter circuit (4 Trotter steps, no AQC)\n",
        "isa_baseline_circuit = pass_manager.run(baseline_circuit)\n",
        "isa_baseline_observable = observable.apply_layout(isa_baseline_circuit.layout)\n",
        "print(\n",
        "    \"Baseline Trotter circuit depth:\",\n",
        "    isa_baseline_circuit.depth(lambda x: x.operation.num_qubits == 2),\n",
        ")\n",
        "\n",
        "# -------------------------Step 3-------------------------\n",
        "\n",
        "# Submit both circuits in a single job\n",
        "estimator = Estimator(backend)\n",
        "estimator.options.environment.job_tags = [\"TUT_AQCTE\"]\n",
        "\n",
        "job = estimator.run(\n",
        "    [\n",
        "        (isa_circuit, isa_observable),\n",
        "        (isa_baseline_circuit, isa_baseline_observable),\n",
        "    ]\n",
        ")\n",
        "print(\"Job ID:\", job.job_id())"
      ]
    },
    {
      "cell_type": "code",
      "execution_count": 15,
      "id": "a4dc23fd-494e-46cb-a8f5-d1cd444b96f4",
      "metadata": {},
      "outputs": [
        {
          "name": "stdout",
          "output_type": "stream",
          "text": [
            "Exact (MPS):        -0.7387\n",
            "Baseline Trotter:   -0.5955, |Δ| = 0.1432\n",
            "AQC (3+1):          -0.6734, |Δ| = 0.0653\n"
          ]
        },
        {
          "data": {
            "text/plain": [
              "<Image src=\"/docs/images/tutorials/approximate-quantum-compilation-for-time-evolution/extracted-outputs/a4dc23fd-494e-46cb-a8f5-d1cd444b96f4-1.avif\" alt=\"Output of the previous code cell\" />"
            ]
          },
          "metadata": {},
          "output_type": "display_data"
        }
      ],
      "source": [
        "# -------------------------Step 4-------------------------\n",
        "\n",
        "hw_results = job.result()\n",
        "aqc_expval = hw_results[0].data.evs.tolist()\n",
        "baseline_expval = hw_results[1].data.evs.tolist()\n",
        "\n",
        "print(f\"Exact (MPS):        {exact_expval:.4f}\")\n",
        "print(\n",
        "    f\"Baseline Trotter:   {baseline_expval:.4f}, |\\u0394| = {np.abs(exact_expval - baseline_expval):.4f}\"\n",
        ")\n",
        "print(\n",
        "    f\"AQC (3+1):          {aqc_expval:.4f}, |\\u0394| = {np.abs(exact_expval - aqc_expval):.4f}\"\n",
        ")\n",
        "\n",
        "labels = [\n",
        "    f\"Baseline Trotter\\n({baseline_num_trotter_steps} steps, depth {isa_baseline_circuit.depth(lambda x: x.operation.num_qubits == 2)})\",\n",
        "    f\"AQC (3+1)\\n(depth {isa_circuit.depth(lambda x: x.operation.num_qubits == 2)})\",\n",
        "]\n",
        "values = [baseline_expval, aqc_expval]\n",
        "colors = [\"tab:orange\", \"tab:blue\"]\n",
        "\n",
        "plt.figure(figsize=(8, 5))\n",
        "bars = plt.bar(labels, values, color=colors, width=0.5)\n",
        "plt.axhline(\n",
        "    y=exact_expval,\n",
        "    color=\"tab:green\",\n",
        "    linestyle=\"--\",\n",
        "    linewidth=2,\n",
        "    label=f\"Exact ({exact_expval:.4f})\",\n",
        ")\n",
        "plt.ylabel(\"Expected Value\")\n",
        "plt.title(\n",
        "    \"AQC-Tensor (3 compressed + 1 uncompressed) vs Baseline Trotter (50-site XXZ)\"\n",
        ")\n",
        "plt.legend()\n",
        "for bar in bars:\n",
        "    y_val = bar.get_height()\n",
        "    plt.text(\n",
        "        bar.get_x() + bar.get_width() / 2.0,\n",
        "        y_val,\n",
        "        f\"{y_val:.4f}\",\n",
        "        ha=\"center\",\n",
        "        va=\"bottom\" if y_val >= 0 else \"top\",\n",
        "    )\n",
        "plt.axhline(y=0, color=\"black\", linewidth=0.3)\n",
        "plt.tight_layout()\n",
        "plt.show()"
      ]
    },
    {
      "cell_type": "markdown",
      "id": "278bc002",
      "metadata": {},
      "source": [
        "<span id=\"next-steps\" />\n",
        "\n",
        "## Nächste Schritte\n",
        "\n",
        "<Admonition type=\"tip\" title=\"Empfehlungen\">\n",
        "  Wenn Sie diese Arbeit interessant fanden, könnten Sie auch an folgenden Materialien interessiert sein:\n",
        "\n",
        "  * [Dokumentation zum AQC-Tensor-Add-on](https://qiskit.github.io/qiskit-addon-aqc-tensor/) – umfasst die zugehörige **unitarische AQC** -Technik, die parametrisierte Schaltkreise so optimiert, dass sie einen angestrebten unitarischen Operator anstelle eines vorbereiteten Zustands approximieren\n",
        "  * [Techniken zur Fehlerminderung und -unterdrückung](/docs/guides/error-mitigation-and-suppression-techniques)\n",
        "  * [Fehlerbehebungstechniken kombinieren](/docs/tutorials/combine-error-mitigation-techniques)\n",
        "</Admonition>\n",
        "\n"
      ]
    },
    {
      "cell_type": "markdown",
      "metadata": {},
      "id": "a1b8767d",
      "source": "© IBM Corp., 2017-2026"
    }
  ],
  "metadata": {
    "description": "Learn how to use AQC-Tensor to compress Trotterized time-evolution circuits for efficient execution on quantum hardware.",
    "kernelspec": {
      "display_name": "Python 3",
      "language": "python",
      "name": "python3"
    },
    "language_info": {
      "codemirror_mode": {
        "name": "ipython",
        "version": 3
      },
      "file_extension": ".py",
      "mimetype": "text/x-python",
      "name": "python",
      "nbconvert_exporter": "python",
      "pygments_lexer": "ipython3",
      "version": "3"
    },
    "title": "Approximate quantum compilation for time evolution circuits",
    "hours": 1.5,
    "qpuSeconds": 15
  },
  "nbformat": 4,
  "nbformat_minor": 5
}