Directly measured squeeze factors over GHz bandwidth from monolithic ppKTP resonators

TL;DR

This paper reports the first direct measurement of 3 dB squeezing factors over a GHz bandwidth in monolithic ppKTP resonators, advancing ultrafast quantum sensing and secure quantum communication.

Contribution

It demonstrates the first direct measurement of GHz-bandwidth squeezing factors in monolithic ppKTP resonators using two laboratory-built homodyne detectors.

Findings

Achieved 3 dB squeezing over GHz bandwidths.

Reproducible results across two different systems.

Spectral differences observed between systems.

Abstract

Squeezed vacuum states of light with bandwidths in the gigahertz range are required for ultrafast quantum sensors, for high-bandwidth QKD and for optical quantum computers. Here we present squeeze factors of monolithic periodically poled KTP (ppKTP) resonators measured with two laboratory-built balanced homodyne detectors with gigahertz bandwidth. We realise two complete systems without selection of optical or electronic hardware components to test the reproducibility without rejects. As expected, the systems show clear spectral differences. However, both achieve directly measured squeeze factors in the order of 3 dB over a GHz bandwidth, which is achieved here for the first time. Our direct measurement of quantum correlation is suitable for increasing the key rate of one-sided, device-independent QKD.