Improvement of Squeezing using a Spatial Phase Modulator and Machine Learning

Squeezed light is an important resource for quantum information processing using continuous variables. When pulsed light is used as a light source to generate squeezed light, sequential information processing can naturally be executed because a single pulse can be regarded as a single mode. In addition, using an optical waveguide as a nonlinear medium not only suppresses the gain induced diffraction [2] but also leads to photonic integration in future.

To achieve high squeezing levels, it is necessary to improve the temporal and spatial mode matching between the squeezed light and the local oscillator (LO) used in homodyne measurements. As for the temporal mode, temporal shaping of the LO pulse enables almost unity efficiency and squeezing of -5.0 dB was reported using waveguides with a pulsed light source [1]. On the other hand, improvement of spatial mode matching has remained as a challenge for the case of pulsed single-path amplification in which the bandwidth of squeezing is wide.

In the present paper, we report on the achievement of squeezing level of -5.88 dB by controlling the spatial phase distribution of the LO beam using a spatial light modulator (SLM) and machine learning. This is the highest value for a pulsed light source, updating the value recorded in 1994 [2].