Measurement-assisted non-Gaussian gate for Schrödinger cat states preparation: Fock resource state versus cubic phase state

Abstract: In this paper, we consider the preparation of Schr\"odinger cat states using a measurement-assisted gate based on the Fock resource state, the quantum non-demolition (QND) entangling operation, and the homodyne measurement. Previously we have investigated the gate, which for the same goal uses the ancillary non-Gaussian cubic phase state generated from quadrature squeezed states at realistic (finite) squeezing. It is of evident interest to compare the efficiency of both schemes, that is, their ability to produce cat-like superpositions with high fidelity and probability of success. We introduce, in parallel with the exact theoretical description of the gate operation, a clear visual interpretation of the output state based on the semiclassical mapping of the input field variables. The emergence of the superpositions of copies of the input state in both schemes is due to the fact that such mapping is compatible with two (or, in general, more) sets of values of the output field observables. We demonstrate that even fine details of the output of both gates are effectively predicted and interpreted in our approach. We examine the fidelity and success probability and reveal the ranges of physical parameters where the Fock state-based and the cubic phase state-based gates demonstrate comparable fidelity and (or) probability of success.