src/setups/decompositions/sqrtswap2cnot.js

import assert from 'assert'
import DecompositionRule from '../../cengines/replacer/decompositionrule'
import {CNOT, SqrtSwapGate, SqrtX} from '../../ops'
import {len} from '../../libs/polyfill'
import {Compute, Control, Uncompute} from '../../meta'
import {tuple} from '../../libs/util'

/**
 * Decompose (controlled) swap gates.
 * @param {Command} cmd
 * @private
 */
function _decompose_sqrtswap(cmd) {
  assert(len(cmd.qubits) === 2 && len(cmd.qubits[0]) === 1 && len(cmd.qubits[1]) === 1)
  const ctrl = cmd.controlQubits
  const qubit0 = cmd.qubits[0][0]
  const qubit1 = cmd.qubits[1][0]
  const eng = cmd.engine

  Control(eng, ctrl, () => {
    Compute(eng, () => {
      CNOT.or(tuple(qubit0, qubit1))
    })
    Control(eng, qubit1, () => {
      SqrtX.or(qubit0)
    })

    Uncompute(eng)
  })
}

export default [
  new DecompositionRule(SqrtSwapGate, _decompose_sqrtswap)
]