Generation of highly pure Schr\"odinger's cat states and real-time quadrature measurements via optical filtering

TL;DR

This paper presents a novel narrowband filtering technique for generating highly pure Schr"odinger's cat states, achieving record purity levels and enabling real-time quadrature measurements, advancing quantum state engineering.

Contribution

The authors introduce a new photon subtraction method with a narrowband filtering cavity, significantly improving the purity of Schr"odinger's cat states and enabling real-time quadrature measurements.

Findings

Achieved a Wigner function value of -0.184 at the origin, the highest reported without loss correction.

Generated a temporally rising mode allowing real-time quadrature measurement.

Demonstrated improved purity over previous methods.

Abstract

Until now, Schr\"odinger's cat states are generated by subtracting single photons from the whole bandwidth of squeezed vacua. However, it was pointed out recently that the achievable purities are limited in such method (J. Yoshikawa, W. Asavanant, and A. Furusawa, arXiv:1707.08146 [quant-ph] (2017)). In this paper, we used our new photon subtraction method with a narrowband filtering cavity and generated a highly pure Schr\"odinger's cat state with the value of $-0.184$ at the origin of the Wigner function. To our knowledge, this is the highest value ever reported without any loss corrections. The temporal mode also becomes exponentially rising in our method, which allows us to make a real-time quadrature measurement on Schr\"odinger's cat states, and we obtained the value of $-0.162$ at the origin of the Wigner function.