Creation and manipulation of Schrödinger cat states based on semiclassical predictions

Abstract: We consider the generation of Schr\"odinger cat states using a quantum measurement-induced logical gate where entanglement between the input state of the target oscillator and the Fock state of the ancillary system produced by the quantum non-demolition entangling $C_Z$ operation is combined with the homodyne measurement. We utilize the semiclassical approach to construct both the input-output mapping of the field variables in the phase space and the wave function of the output state. This approach is found to predict that the state at the gate output is represented by a minimum disturbed cat-like state which is a superposition of two initial state copies symmetrically displaced by momentum variable. For the target oscillator prepared in the coherent state, we show that the fidelity between the exact solution for the gate output state and the "perfect" Schr\"odinger cat reconstructed from the semiclassical theory can reach high values exceeding 0.99.