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      "source": [
        "---\n",
        "title: \"量子ビットを測定する\"\n",
        "description: \"量子ビットの測定方法、および測定が使用できる場所に関する制約について学びます。\"\n",
        "---\n",
        "\n",
        "<span id=\"measure-qubits\" />\n",
        "\n",
        "# 量子ビットを測定する\n",
        "\n"
      ]
    },
    {
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      "metadata": {
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          "version-info"
        ]
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      "source": [
        "{/*\n",
        "  DO NOT EDIT THIS CELL!!!\n",
        "  This cell's content is generated automatically by a script. Anything you add\n",
        "  here will be removed next time the notebook is run. To add new content, create\n",
        "  a new cell before or after this one.\n",
        "  */}\n",
        "\n",
        "<Accordion>\n",
        "  <AccordionItem title=\"パッケージ・バージョン\">\n",
        "    このページのコードは、以下の要件に基づいて開発された。\n",
        "    これらのバージョンまたは新しいバージョンの使用をお勧めします。\n",
        "\n",
        "    ```\n",
        "    qiskit[all]~=2.5.1\n",
        "    ```\n",
        "  </AccordionItem>\n",
        "</Accordion>\n",
        "\n"
      ]
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        "量子ビットの状態に関する情報を得るには、それを[古典ビットの](/docs/api/qiskit/circuit#qiskit.circuit.Clbit)上で*測定*すればよい。 Qiskitでは、測定は計算基底、すなわち1量子ビットPauli- $Z$ 基底で行われる。 したがって、パウリ $Z$ 固有状態 $|0\\rangle$ と $|1\\rangle$ との重なりによって、測定結果は0か1になる：\n",
        "\n",
        "$$\n",
        "|q\\rangle \\xrightarrow{measure}\\begin{cases}\n",
        "      0 (\\text{outcome}+1), \\text{with probability } p_0=|\\langle q|0\\rangle|^{2}\\text{,} \\\\\n",
        "      1 (\\text{outcome}-1), \\text{with probability } p_1=|\\langle q|1\\rangle|^{2}\\text{.}\n",
        "    \\end{cases}\n",
        "$$\n",
        "\n",
        "<span id=\"apply-a-measurement-to-a-circuit\" />\n",
        "\n",
        "## 回路に測定を適用する\n",
        "\n",
        "回路に測定を適用する方法はいくつかある：\n",
        "\n",
        "<span id=\"quantumcircuitmeasure-method\" />\n",
        "\n",
        "### `QuantumCircuit.measure`メソッド\n",
        "\n",
        "を使用する。 [`measure`](/docs/api/qiskit/qiskit.circuit.QuantumCircuit#measure) メソッドを使って [`QuantumCircuit`](/docs/api/qiskit/qiskit.circuit.QuantumCircuit#quantumcircuit-class).\n",
        "\n",
        "例：\n",
        "\n"
      ]
    },
    {
      "cell_type": "code",
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      "id": "6cc3aa2f-40a5-4191-8236-a5ffd2e64be0",
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              "<qiskit.circuit.instructionset.InstructionSet at 0x7ff250007af0>"
            ]
          },
          "execution_count": 1,
          "metadata": {},
          "output_type": "execute_result"
        }
      ],
      "source": [
        "from qiskit import QuantumCircuit\n",
        "\n",
        "qc = QuantumCircuit(5, 5)\n",
        "qc.x(0)\n",
        "qc.x(1)\n",
        "qc.x(4)\n",
        "qc.measure(\n",
        "    range(5), range(5)\n",
        ")  #  Measures all qubits into the corresponding clbit."
      ]
    },
    {
      "cell_type": "code",
      "execution_count": 2,
      "id": "5c629673-9000-47ae-8bd3-f3fef65f8b0c",
      "metadata": {},
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        {
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            "text/plain": [
              "<qiskit.circuit.instructionset.InstructionSet at 0x7ff250007ca0>"
            ]
          },
          "execution_count": 2,
          "metadata": {},
          "output_type": "execute_result"
        }
      ],
      "source": [
        "from qiskit import QuantumCircuit\n",
        "\n",
        "qc = QuantumCircuit(3, 1)\n",
        "qc.x([0, 2])\n",
        "qc.measure(1, 0)  # Measure qubit 1 into the classical bit 0."
      ]
    },
    {
      "cell_type": "markdown",
      "id": "d909843d-9c23-4017-83d6-8a09fae4c067",
      "metadata": {},
      "source": [
        "<span id=\"measure-class\" />\n",
        "\n",
        "### `Measure` クラス\n",
        "\n",
        "Qiskit [Measure](/docs/api/qiskit/circuit#qiskit.circuit.Measure) クラスは、指定された量子ビットを測定します。\n",
        "\n"
      ]
    },
    {
      "cell_type": "code",
      "execution_count": 3,
      "id": "b8855eed-8238-41ce-a45d-f8e81da05508",
      "metadata": {},
      "outputs": [
        {
          "data": {
            "text/plain": [
              "<qiskit.circuit.instructionset.InstructionSet at 0x7ff250007760>"
            ]
          },
          "execution_count": 3,
          "metadata": {},
          "output_type": "execute_result"
        }
      ],
      "source": [
        "from qiskit.circuit import Measure\n",
        "\n",
        "qc = QuantumCircuit(3, 1)\n",
        "qc.x([0, 1])\n",
        "qc.append(Measure(), [0], [0])  # measure qubit 0 into clbit 0"
      ]
    },
    {
      "cell_type": "markdown",
      "id": "6583286c-d8e3-4adf-8bce-0e7d9dc3c44f",
      "metadata": {},
      "source": [
        "<span id=\"quantumcircuitmeasure_all-method\" />\n",
        "\n",
        "### `QuantumCircuit.measure_all`メソッド\n",
        "\n",
        "すべての量子ビットを対応する古典ビットに変換するには [`measure_all`](/docs/api/qiskit/qiskit.circuit.QuantumCircuit#measure_all) メソッドを使う。 デフォルトでは、この方法はこれらの測定値を保存するために、 `ClassicalRegister` に新しいクラシックビットを追加する。\n",
        "\n"
      ]
    },
    {
      "cell_type": "code",
      "execution_count": 4,
      "id": "cac45158-7e3e-47b6-bc89-8ac3a4bc9539",
      "metadata": {},
      "outputs": [],
      "source": [
        "from qiskit import QuantumCircuit\n",
        "\n",
        "qc = QuantumCircuit(3, 1)\n",
        "qc.x([0, 2])\n",
        "qc.measure_all()  # Measure all qubits."
      ]
    },
    {
      "cell_type": "markdown",
      "id": "8b4a57d5-ffc9-4247-b39c-2e19ab2c185b",
      "metadata": {},
      "source": [
        "<span id=\"quantumcircuitmeasure_active-method\" />\n",
        "\n",
        "### `QuantumCircuit.measure_active`メソッド\n",
        "\n",
        "アイドル状態でないすべての量子ビットを測定するには [`measure_active`](/docs/api/qiskit/qiskit.circuit.QuantumCircuit#measure_active) メソッドを使います。 このメソッドは、測定中の非アイドル量子ビットの数に等しいサイズの新しい `ClassicalRegister` 。\n",
        "\n"
      ]
    },
    {
      "cell_type": "code",
      "execution_count": 5,
      "id": "3161f70d-5c59-48fa-842f-624ce7ed0bbe",
      "metadata": {},
      "outputs": [],
      "source": [
        "from qiskit import QuantumCircuit\n",
        "\n",
        "qc = QuantumCircuit(3, 1)\n",
        "qc.x([0, 2])\n",
        "qc.measure_active()  # Measure qubits that are not idle, that is, qubits 0 and 2."
      ]
    },
    {
      "cell_type": "markdown",
      "id": "5b049296-7cd5-4074-8473-ad462744e270",
      "metadata": {},
      "source": [
        "<span id=\"next-steps\" />\n",
        "\n",
        "## 次のステップ\n",
        "\n",
        "<Admonition type=\"tip\" title=\"推奨事項\">\n",
        "  * [`Measure`](/docs/api/qiskit/circuit#qiskit.circuit.Measure) クラス\n",
        "  * [`measure_all`](/docs/api/qiskit/qiskit.circuit.QuantumCircuit#measure_all) 方法\n",
        "  * [`measure_active`](/docs/api/qiskit/qiskit.circuit.QuantumCircuit#measure_active) 方法\n",
        "  * [`random_circuit`](/docs/api/qiskit/circuit_random#qiskit.circuit.random.random_circuit) 方法\n",
        "  * [回路中間点での測定](/docs/guides/execute-dynamic-circuits#midcircuit) （ IBM Quantum Compute Service を使用している場合のみ利用可能です。）\n",
        "</Admonition>\n",
        "\n"
      ]
    },
    {
      "cell_type": "markdown",
      "metadata": {},
      "id": "a1b8767d",
      "source": "© IBM Corp., 2017-2026"
    }
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