const T = 20, N = 60, dt = T / N;
const c = circuit(1);
c.h(0); // ground state of the driver -X is |+>
for (let k = 0; k < N; k++) {
  const s = (k + 0.5) / N;
  c.rz(-2 * dt * s, 0);        // e^{i dt s Z}
  c.rx(-2 * dt * (1 - s), 0);  // e^{i dt (1-s) X}
}
c.measure();
return c;