THE BIRTH OF A PHASE-CAT

We present a recipe for constructing a phase-cat, that is a superposit ion of two coherent states of identical phase but different amplitudes . The method relies on an effective rotation of an amplitude-cat, that is a superposition of two coherent states with identical amplitudes b ut different phases. We create the amplitude-cat by a dispersive atom- field interaction and achieve its effective rotation via the combinati on of two beam splitters and a phase shifter. We optimize the amount o f phase narrowing by choosing the appropriate initial atomic superposi tion and by performing the appropriate delayed measurement of the fina l atomic coherence.