{
  "schema": "wai.quantum.exercise/1",
  "id": "phase",
  "translations": { "zh-CN": "machine-assisted: to be reviewed by a fluent reader before it is advertised" },
  "title": { "en": "A phase you cannot see, until you interfere", "zh-CN": "看不见的相位，直到干涉发生" },
  "task": {
    "en": "One qubit. Using only h and z, make its measurement give 1 every time.",
    "zh-CN": "一个量子比特。只用 h 和 z，让它的测量每次都给出 1。"
  },
  "starter": [
    "OPENQASM 3.0;",
    "include \"stdgates.inc\";",
    "qubit[1] q;",
    "bit[1] c;",
    "h q[0];",
    "c = measure q;"
  ],
  "intent": { "distribution": { "1": 1.0 } },
  "constraints": { "allow": ["h", "z"] },
  "hints": {
    "en": [
      "z leaves |0⟩ alone and flips the sign of |1⟩. On (|0⟩ + |1⟩)/√2 it changes nothing a measurement can see.",
      "A second Hadamard turns a sign between |0⟩ and |1⟩ into a difference in outcomes."
    ],
    "zh-CN": [
      "z 不改变 |0⟩，而把 |1⟩ 的符号取反。作用在 (|0⟩ + |1⟩)/√2 上时，它不改变任何测量能看到的东西。",
      "第二个 Hadamard 门会把 |0⟩ 与 |1⟩ 之间的符号差别变成结果上的差别。"
    ]
  },
  "reference": [
    "OPENQASM 3.0;",
    "include \"stdgates.inc\";",
    "qubit[1] q;",
    "bit[1] c;",
    "h q[0];",
    "z q[0];",
    "h q[0];",
    "c = measure q;"
  ],
  "wrong": [
    {
      "fails": "intent",
      "note": "the sign is there, but nothing interferes it into an outcome",
      "qasm": ["OPENQASM 3.0;", "include \"stdgates.inc\";", "qubit[1] q;", "bit[1] c;", "h q[0];", "z q[0];", "c = measure q;"]
    },
    {
      "fails": "constraint",
      "note": "x gives 1, but the exercise allows only h and z",
      "qasm": ["OPENQASM 3.0;", "include \"stdgates.inc\";", "qubit[1] q;", "bit[1] c;", "x q[0];", "c = measure q;"]
    }
  ]
}