{
  "cells": [
    {
      "cell_type": "markdown",
      "id": "dd701ecc",
      "metadata": {},
      "source": [
        "---\n",
        "title: \"Compilación cuántica aproximada para circuitos de evolución temporal\"\n",
        "description: \"Descubre cómo utilizar AQC-Tensor para comprimir circuitos de evolución temporal «trotterizados» y lograr una ejecución eficiente en hardware cuántico.\"\n",
        "---\n",
        "\n",
        "{/* cspell:ignore circo Néel */}\n",
        "\n",
        "<span id=\"approximate-quantum-compilation-for-time-evolution-circuits\" />\n",
        "\n",
        "# Compilación cuántica aproximada para circuitos de evolución temporal\n",
        "\n",
        "*Tiempo estimado de ejecución: 15 segundos en un procesador Heron (NOTA: Se trata únicamente de una estimación). (El tiempo de ejecución puede variar.)*\n",
        "\n"
      ]
    },
    {
      "cell_type": "markdown",
      "id": "12608301",
      "metadata": {},
      "source": [
        "<span id=\"learning-outcomes\" />\n",
        "\n",
        "## Resultados del aprendizaje\n",
        "\n",
        "Una vez completado este tutorial, habrás adquirido los siguientes conocimientos:\n",
        "\n",
        "* Cómo utilizar el complemento AQC-Tensor de Qiskit para comprimir circuitos de Trotter profundos en circuitos de ansatz superficiales\n",
        "* Cómo generar un ansatz parametrizado a partir de un circuito de Trotter y optimizar sus parámetros mediante métodos de redes tensoriales (MPS)\n",
        "* Cómo evaluar la fidelidad de un circuito comprimido con respecto a la evolución objetivo y ejecutarlo en hardware cuántico\n",
        "\n"
      ]
    },
    {
      "cell_type": "markdown",
      "id": "c3c5992a",
      "metadata": {},
      "source": [
        "<span id=\"prerequisites\" />\n",
        "\n",
        "## Requisitos previos\n",
        "\n",
        "Se recomienda que te familiarices con estos temas:\n",
        "\n",
        "* [Conceptos básicos de los circuitos cuánticos](/learning/courses/basics-of-quantum-information)\n",
        "* [Simulación hamiltoniana y trotterización](/learning/courses/utility-scale-quantum-computing/quantum-simulation)\n",
        "* [Introducción a las primitivas](/docs/guides/primitives)\n",
        "\n"
      ]
    },
    {
      "cell_type": "markdown",
      "id": "714adc39",
      "metadata": {},
      "source": [
        "<span id=\"background\" />\n",
        "\n",
        "## En segundo plano\n",
        "\n",
        "Este tutorial muestra cómo implementar **la compilación cuántica aproximada** mediante redes tensoriales (AQC-Tensor) con Qiskit para mejorar el rendimiento de los circuitos cuánticos. AQC-Tensor comprime los circuitos Trotter profundos en circuitos menos profundos y más compatibles con el hardware, al tiempo que mantiene la precisión de la simulación.\n",
        "\n",
        "<span id=\"how-aqc-tensor-works\" />\n",
        "\n",
        "### Cómo funciona AQC-Tensor\n",
        "\n",
        "Consideremos la simulación de un hamiltoniano $H$ durante un tiempo total de $t$ utilizando $k$ pasos de Trotter. El circuito completo de Trotter es:\n",
        "\n",
        "$$\n",
        "U_{\\text{full}} = \\left[U_{\\text{Trotter}}(t/k)\\right]^k\n",
        "$$\n",
        "\n",
        "Un enfoque simplista utiliza pocos pasos de Trotter para que la profundidad del circuito sea manejable, pero esto da lugar a un error de Trotter considerable. AQC-Tensor resuelve esta tensión separando la precisión de la profundidad:\n",
        "\n",
        "1. **Circuito de referencia (alta precisión, profundo):** Construye un circuito de Trotter con muchos pasos —por ejemplo, $10k$ — para el mismo tiempo de evolución. Este circuito presenta un error de Trotter mucho menor, pero es demasiado complejo para implementarlo en hardware. Dado que solo se simula de forma clásica como un estado de producto matricial (MPS), la profundidad no supone ningún problema.\n",
        "\n",
        "2. **Circuito de Ansatz (poca profundidad, parametrizado):** Define un circuito parametrizado $V(\\theta)$ con la misma estructura que un circuito de Trotter de un solo paso. Inicialízalo de modo que $V(\\theta_{\\text{init}}) = U_{\\text{Trotter}}(t/k)$, y luego optimiza iterativamente $\\theta$ para que $V(\\theta)$ reproduzca el estado objetivo de alta precisión con la mayor precisión posible.\n",
        "\n",
        "El resultado es un circuito que conserva la profundidad de un solo paso de Trotter, pero alcanza la precisión de muchos, lo que lo hace viable para el hardware cuántico a corto plazo.\n",
        "\n",
        "<span id=\"when-to-use-aqc-tensor\" />\n",
        "\n",
        "### Cuándo utilizar AQC-Tensor\n",
        "\n",
        "AQC-Tensor resulta más eficaz cuando:\n",
        "\n",
        "* **La profundidad del circuito supera los tiempos de coherencia del hardware.** Si una simulación de Trotter requiere más pasos de Trotter de los que el dispositivo puede admitir, AQC-Tensor puede comprimir la evolución en un circuito de menor profundidad.\n",
        "* **El entrelazamiento sigue siendo manejable desde el punto de vista clásico.** El entrelazamiento total en un estado evolucionado en el tiempo depende principalmente del tiempo de evolución $t$, y no del número de pasos de Trotter $k$. Esto significa que un circuito objetivo con $10k$ pasos no suele ser más difícil de representar como un MPS que uno con $k$ pasos, siempre y cuando $t$ sea lo suficientemente corto como para que las dimensiones de los enlaces sigan siendo manejables.\n",
        "* **Existe un enfoque natural.** Dado que el enfoque refleja la estructura de un circuito de Trotter, ofrece un punto de partida con base física y parámetros iniciales bien definidos, lo que permite evitar los problemas de convergencia que pueden afectar a los enfoques variacionales arbitrarios.\n",
        "\n",
        "Este enfoque contrasta con la compresión de circuitos genérica: en lugar de intentar aproximar un operador unitario arbitrario con menos puertas lógicas, AQC-Tensor mantiene la misma estructura de puertas y optimiza sus parámetros para reducir el error de Trotter. Consulte la [documentación de AQC-Tensor](https://qiskit.github.io/qiskit-addon-aqc-tensor/) para obtener más información.\n",
        "\n",
        "Este tutorial te guía a lo largo de todo el flujo de trabajo de preparación de estados de AQC-Tensor: definición de un hamiltoniano, generación de circuitos de Trotter, compresión de estos mediante optimización de redes tensoriales y ejecución del resultado en un hardware de tip IBM Quantum®.\n",
        "\n"
      ]
    },
    {
      "cell_type": "markdown",
      "id": "f8a05291",
      "metadata": {},
      "source": [
        "<span id=\"requirements\" />\n",
        "\n",
        "## Requisitos\n",
        "\n",
        "Antes de empezar este tutorial, asegúrate de que tienes instalado lo siguiente:\n",
        "\n",
        "* Qiskit SDK v2.0 o posterior, con soporte [para visualización](/docs/en/api/qiskit/visualization)\n",
        "* Qiskit Runtime v0.22 o posterior (`pip install qiskit-ibm-runtime`)\n",
        "* AQC-Tensor Qiskit addon (`pip install 'qiskit-addon-aqc-tensor[aer,quimb-jax]'`)\n",
        "\n"
      ]
    },
    {
      "cell_type": "markdown",
      "id": "f9410d21",
      "metadata": {},
      "source": [
        "<span id=\"setup\" />\n",
        "\n",
        "## Configuración\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",
        "## Ejemplo de simulador a pequeña escala\n",
        "\n",
        "En esta sección se utiliza un sistema de 10 puntos para explicar paso a paso el flujo de trabajo de AQC-Tensor. Simulamos la dinámica de una cadena de espines XXZ de 10 nodos, un modelo ampliamente estudiado para analizar las interacciones de espín y las propiedades magnéticas.\n",
        "\n",
        "El hamiltoniano es el siguiente:\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",
        "donde $J_{i,(i+1)}$ es un coeficiente aleatorio para el borde $(i, i+1)$ y $L=10$.\n",
        "\n"
      ]
    },
    {
      "cell_type": "markdown",
      "id": "6520161e",
      "metadata": {},
      "source": [
        "<span id=\"step-1-map-classical-inputs-to-a-quantum-problem\" />\n",
        "\n",
        "### Paso 1: Asignar entradas clásicas a un problema cuántico\n",
        "\n",
        "En este paso, hacemos lo siguiente:\n",
        "\n",
        "1. Define el hamiltoniano, la observable y el estado inicial.\n",
        "2. Calcula el valor exacto de la esperanza matemática mediante el método clásico para poder compararlo más adelante.\n",
        "3. Genera un circuito de Trotter de alta precisión (el objetivo de AQC) y comprímelo en un ansatz de baja profundidad utilizando AQC-Tensor.\n",
        "\n"
      ]
    },
    {
      "cell_type": "markdown",
      "id": "bbeb5729",
      "metadata": {},
      "source": [
        "<span id=\"set-up-the-hamiltonian-observable-and-initial-state\" />\n",
        "\n",
        "#### Establece el hamiltoniano, la observable y el estado inicial\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",
        "#### Calcular el valor exacto de la esperanza\n",
        "\n",
        "Para un sistema de este tamaño, podemos calcular directamente el valor esperado a lo largo del tiempo utilizando la exponenciación de matrices. Esto nos sirve como referencia para evaluar la precisión del circuito AQC.\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",
        "#### Generar el circuito objetivo de AQC\n",
        "\n",
        "Ahora construiremos el circuito de Trotter que servirá como objetivo del AQC. Este circuito utiliza numerosos pasos de Trotter (32) para garantizar una alta precisión. Dado que solo se simulará de forma clásica como un MPS —y no se ejecutará en hardware—, la gran profundidad no supone ningún problema.\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",
        "#### Generar un ansatz, los parámetros iniciales, el circuito resultante y un circuito de referencia\n",
        "\n",
        "A continuación, construimos un circuito «bueno» con el mismo tiempo de evolución que el objetivo del AQC, pero con muchos menos pasos de Trotter (solo uno). Pasamos este circuito a `generate_ansatz_from_circuit`, que devuelve:\n",
        "\n",
        "1. Un circuito **de aproximación** general y parametrizado con la misma conectividad de dos qubits.\n",
        "2. **Parámetros iniciales** que reproducen el circuito de entrada cuando se conectan al ansatz.\n",
        "\n",
        "También construimos:\n",
        "\n",
        "* Un **circuito posterior** con un paso de Trotter que se añadirá (sin comprimir) tras la parte optimizada con AQC, siguiendo el enfoque [del tutorial](https://qiskit.github.io/qiskit-addon-aqc-tensor/tutorials/01_initial_state_aqc.html) sobre el estado inicial de AQC-Tensor.\n",
        "* **Un circuito Trotter de referencia** que utiliza cuatro pasos de Trotter a lo largo de todo el tiempo de evolución (`aqc_evolution_time + subsequent_evolution_time`). Esto sirve como punto de comparación: representa lo que se ejecutaría en hardware sin AQC. El enfoque AQC (3 pasos comprimidos + 1 paso sin comprimir) ofrece una mayor precisión a menor profundidad.\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",
        "#### Configurar la simulación de redes tensoriales y generar el MPS deseado\n",
        "\n",
        "Utilizamos el simulador de circuitos «Matrix-Product State» (MPS) [de Quimb](https://github.com/jcmgray/quimb), y JAX proporciona la diferenciación automática para la optimización basada en gradientes. A continuación, construimos una representación MPS del estado objetivo y evaluamos la fidelidad inicial entre el ansatz inicial y el estado objetivo. Dado que la instancia del problema es un ejemplo relativamente pequeño, el nivel de fidelidad inicial es bastante alto.\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",
        "#### Optimizar los parámetros del ansatz\n",
        "\n",
        "Minimizamos la `MaximizeStateFidelity` función de coste utilizando el optimizador L-BFGS-B. El optimizador ajusta de forma iterativa los parámetros del ansatz para maximizar la fidelidad entre el circuito del ansatz y el MPS objetivo.\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",
        "#### Montar el circuito AQC definitivo\n",
        "\n",
        "Una vez que disponemos de los parámetros optimizados, los aplicamos al ansatz y, a continuación, añadimos el paso de Trotter siguiente (sin comprimir). El circuito resultante tiene la profundidad de un solo paso de Trotter comprimido más un paso sin comprimir, pero la parte comprimida se aproxima a la precisión de 32 pasos de Trotter.\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",
        "### Paso 2: Optimizar el problema para la ejecución en hardware cuántico\n",
        "\n",
        "En este ejemplo a pequeña escala, utilizamos un backend ficticio (`FakeKyiv`) para simular la ejecución en hardware a nivel local. Compilamos tanto el circuito optimizado con AQC (`aqc_final_circuit`) como el circuito Trotter de referencia (`baseline_circuit`, cuatro pasos de Trotter a lo largo de todo el tiempo de evolución, sin AQC) a la arquitectura del conjunto de instrucciones (ISA) del backend, con `optimization_level=3` para reducir aún más la profundidad del circuito.\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",
        "### Paso 3: Ejecutar utilizando Qiskit primitives\n",
        "\n",
        "Utilizamos la [`EstimatorV2`](/docs/api/qiskit-ibm-runtime/estimator-v2) primitiva con el backend simulado para ejecutar tanto el circuito optimizado mediante AQC como el circuito de Trotter de referencia, midiendo la observable ZZ en cada caso.\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",
        "### Paso 4: Procesamiento posterior y devolución del resultado en el formato clásico deseado\n",
        "\n",
        "Extraemos los valores esperados de ambas ejecuciones y los comparamos con el resultado exacto. El circuito Trotter de referencia muestra el resultado que obtendríamos sin AQC con la misma profundidad de circuito, mientras que el circuito AQC ilustra la mejora conseguida gracias a la optimización de redes tensoriales.\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",
        "## Ejemplo de hardware a gran escala\n",
        "\n",
        "Ahora ampliamos el modelo XXZ a 50 sitios para demostrar el funcionamiento de AQC-Tensor con un problema de mayor envergadura. El proceso es el mismo que en el ejemplo a pequeña escala: comprimimos tres pasos de Trotter mediante AQC y añadimos un paso sin comprimir.\n",
        "\n",
        "En un sistema de este tamaño, la exponenciación de matrices resulta inviable (dimensiones $2^{50}$ ), por lo que calculamos el valor esperado de referencia directamente a partir de un MPS de alta precisión que se ha hecho evolucionar durante todo el tiempo.\n",
        "\n",
        "<span id=\"steps-1–4-combined\" />\n",
        "\n",
        "### Pasos 1 a 4 combinados\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",
        "## Próximos pasos\n",
        "\n",
        "<Admonition type=\"tip\" title=\"Recomendaciones\">\n",
        "  Si te ha parecido interesante este trabajo, quizá te interese el siguiente material:\n",
        "\n",
        "  * [Documentación del complemento AQC-Tensor](https://qiskit.github.io/qiskit-addon-aqc-tensor/) : incluye la técnica **AQC unitaria** relacionada, que optimiza circuitos parametrizados para aproximarse a un operador unitario objetivo en lugar de a un estado preparado\n",
        "  * [Técnicas de mitigación y supresión de errores](/docs/guides/error-mitigation-and-suppression-techniques)\n",
        "  * [Combinar técnicas de mitigación de errores](/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
}