Multiple choice
Run this circuit, then measure all 2 qubits at once. What is the probability of the joint outcome |01⟩ (qubit 0 leftmost)?
const J = 1.0, t = 0.5, theta = 2 * J * t; const c = circuit(2); c.x(1); // start in |01> // exp(-i theta/2 Z⊗Z) c.cx(0, 1); c.rz(theta, 1); c.cx(0, 1); // exp(-i theta/2 X⊗X) = (H⊗H) exp(-i theta/2 Z⊗Z) (H⊗H) c.h(0); c.h(1); c.cx(0, 1); c.rz(theta, 1); c.cx(0, 1); c.h(0); c.h(1); // exp(-i theta/2 Y⊗Y) = (RX(pi/2)⊗RX(pi/2)) exp(-i theta/2 Z⊗Z) (RX(-pi/2)⊗RX(-pi/2)) c.rx(Math.PI / 2, 0); c.rx(Math.PI / 2, 1); c.cx(0, 1); c.rz(theta, 1); c.cx(0, 1); c.rx(-Math.PI / 2, 0); c.rx(-Math.PI / 2, 1); return c;
Commit your prediction for P(|01⟩) — then run it.