Even coherent-state superposition
= Even coherent-state superposition
= Even cat state
{synonym}
The normalized sum $N_+(|\alpha\rangle+|-\alpha\rangle)$ contains only even <photon numbers>, since the two coherent-state expansions cancel every odd term. It tends to vacuum at small amplitude. With real $\alpha$, its second quadrature can be squeezed below the vacuum <variance>.