# Generation of monocycle squeezed light in chirped quasi-phase-matched nonlinear crystals

## TL;DR

This paper develops a quantum theory for ultrabroadband squeezed light generation in chirped quasi-phase-matched nonlinear crystals, demonstrating their potential for broad spectral squeezing with near-single-cycle correlation times.

## Contribution

It introduces a new quantum theoretical framework for ultrabroadband squeezed light in chirped nonlinear crystals, validated against exact solutions.

## Key findings

- Good agreement between approximate and exact solutions.
- Aperiodically poled crystals can generate near-single-cycle squeezed light.
- Squeezing bandwidth covers almost entire optical spectrum.

## Abstract

We present a quantum theory of parametric down-conversion of light in chirped quasi-phase-matched second-order nonlinear crystals with undepleted quasi-monochromatic pump. This theory allows us to consider generation of ultrabroadband squeezed states of light and is valid for arbitrary, sufficiently slowly-varying nonlinear poling profiles. Using a first-order approximate quantum solution for the down-converted light field, we calculate the squeezing spectra and the characteristic squeezing angles. We compare the approximate solutions with the exact and numerical ones and find a very good agreement. This comparison validates our approximate solution in the regime of moderate gain, where the existing approaches are not applicable. Our results demonstrate that aperiodically poled crystals are very good candidates for generating ultrabroadband squeezed light with the squeezing bandwidth covering almost all the optical spectrum and the correlation time approaching a single optical cycle.