{
  "schema": "wai.quantum.exercise/1",
  "id": "bell",
  "translations": { "zh-CN": "machine-assisted: to be reviewed by a fluent reader before it is advertised" },
  "title": { "en": "Two qubits, one answer", "zh-CN": "两个量子比特，一个答案" },
  "task": {
    "en": "Two qubits. Make the outcomes 00 and 11 each come up with probability one half, and never 01 or 10.",
    "zh-CN": "两个量子比特。让结果 00 和 11 各以二分之一的概率出现，而 01 和 10 永远不出现。"
  },
  "starter": [
    "OPENQASM 3.0;",
    "include \"stdgates.inc\";",
    "qubit[2] q;",
    "bit[2] c;",
    "// your gates here",
    "c = measure q;"
  ],
  "intent": { "distribution": { "00": 0.5, "11": 0.5 } },
  "hints": {
    "en": [
      "Superposition on both qubits separately gives all four outcomes. The second qubit has to follow the first.",
      "A controlled-NOT flips its target when its control is |1⟩, and leaves it when the control is |0⟩."
    ],
    "zh-CN": [
      "分别让两个量子比特处于叠加会得到全部四个结果。第二个量子比特必须跟随第一个。",
      "受控非门在控制比特为 |1⟩ 时翻转目标比特，在控制比特为 |0⟩ 时保持不变。"
    ]
  },
  "reference": [
    "OPENQASM 3.0;",
    "include \"stdgates.inc\";",
    "qubit[2] q;",
    "bit[2] c;",
    "h q[0];",
    "cx q[0], q[1];",
    "c = measure q;"
  ],
  "wrong": [
    {
      "fails": "intent",
      "note": "independent superpositions give all four outcomes",
      "qasm": ["OPENQASM 3.0;", "include \"stdgates.inc\";", "qubit[2] q;", "bit[2] c;", "h q[0];", "h q[1];", "c = measure q;"]
    }
  ]
}