Function applyQuantumFourierTransform

quest/src/api/operations.cpp:1739–1758

extern "C" {

void applyQuantumFourierTransform(Qureg qureg, int* targets, int numTargets) {
    validate_quregFields(qureg, __func__);
    validate_targets(qureg, targets, numTargets, __func__);

    /// @todo
    /// change this placeholder implementation to the bespoke, optimised routine,
    /// wherein each contiguous controlled-phase gate is merged

    for (int n=numTargets-1; n>=0; n--) {
        applyHadamard(qureg, targets[n]);
        for (int m=0; m<n; m++) {
            qreal arg = const_PI / powerOf2(m+1);
            applyTwoQubitPhaseShift(qureg, targets[n], targets[n-m-1], arg);
        }
    }

    int mid = numTargets/2; // floors
    for (int n=0; n<mid; n++)
        applySwap(qureg, targets[n], targets[numTargets-1-n]);
}

void applyFullQuantumFourierTransform(Qureg qureg) {
    validate_quregFields(qureg, __func__);