Efficient Optical Generation of Large-Amplitude Schrödinger Cat States with Minimal Resources

Abstract

We demonstrate a protocol enabling the generation of large coherent state superpositions with unprecedented preparation rate. It is optimally using expensive non-Gaussian resources to build up only the core non-Gaussian part of the state.Non-Gaussian states of light -such as coherent states superposition (CSS) of the form |α ± | − α with |α a coherent states with mean photon number value |α| 2 , also sometimes called optical Schrödinger cat states-are critical resources in the emerging field of optical hybrid quantum information [1,2]. A well-known and seminal protocol to generate odd optical CSS of size |α| 2 ∼ 1 is based on photon subtraction operated on squeezed vacuum state. To reach higher mean photon values, experiments have focused on multiple subtractions or cascaded conditionings. In all the reported approaches to date, the generation rate is intrinsically low, at the Hz level or below, precluding their use in subsequent protocols.Here we demonstrate the experimental realization of large-amplitude even squeezed Schrödinger cat states with a size |α| 2 = 3 and a fidelity of 67%. The generated state exhibits the highest amplitude and fidelity reported to date for free-propagating CSS, and importantly a preparation rate about 200 Hz is achieved, as we recently reported in [3]. These observations are made possible by implementing a strategy focusing all the non-Gaussian resources to prepare only the non-Gaussian part of the state, and by the combination of a large escape efficiency optical parametric oscillator and high-efficiency superconducting nanowire single-photon detectors.