Rotation gates implementation using cuStateVec. The example applies $R_x(\pi/2)$ to $\lvert 0\rangle$, producing $\frac{1}{\sqrt{2}}(\lvert 0\rangle - i\lvert 1\rangle)$.

// Compile: nvcc main.cu -o main -lcustatevec
// Run:     ./main
 
#include <stdio.h>
#include <math.h>
#include <cuda_runtime.h>
#include <custatevec.h>
 
int main() {
    const int nQubits = 1;
    const int dim = 1 << nQubits;
 
    cuDoubleComplex h_sv[2] = {{1,0},{0,0}};  // |0>
    cuDoubleComplex *d_sv;
    cudaMalloc(&d_sv, dim * sizeof(cuDoubleComplex));
    cudaMemcpy(d_sv, h_sv, dim * sizeof(cuDoubleComplex), cudaMemcpyHostToDevice);
 
    custatevecHandle_t handle;
    custatevecCreate(&handle);
 
    // R_x(pi/2): cos(pi/4)I - i*sin(pi/4)X
    double c = cos(M_PI / 4.0);
    double s = sin(M_PI / 4.0);
    cuDoubleComplex gate[4] = {{c,0},{0,-s},{0,-s},{c,0}};
    int32_t targets[] = {0};
    custatevecApplyMatrix(
        handle, d_sv, CUDA_C_64F, nQubits,
        gate, CUDA_C_64F, CUSTATEVEC_MATRIX_LAYOUT_ROW, 0,
        targets, 1, NULL, NULL, 0,
        CUSTATEVEC_COMPUTE_64F, NULL, 0);
 
    cudaMemcpy(h_sv, d_sv, dim * sizeof(cuDoubleComplex), cudaMemcpyDeviceToHost);
    for (int i = 0; i < dim; i++)
        printf("|%d>: (%.4f, %.4f)\n", i, cuCreal(h_sv[i]), cuCimag(h_sv[i]));
    // |0>: ( 0.7071,  0.0000)
    // |1>: ( 0.0000, -0.7071)  <- (|0> - i|1>) / sqrt(2)
 
    custatevecDestroy(handle);
    cudaFree(d_sv);
    return 0;
}