Squeezed states can be employed for entanglement-based continuous-variable quantum key distribution, where the secure key rate is proportional to the bandwidth of the squeezing. We produced a non-classical continuous-wave laser field at the telecommunication wavelength of 1550 nm, which showed squeezing over a bandwidth of more than 2 GHz. The experimental setup used parametric down-conversion via a periodically poled potassium titanyl phosphate crystal (PPKTP). We did not use any resonant enhancement for the funda- mental wavelength, which should in principle allow a production of squeezed light over the full phase-matching bandwidth of several nanometers. We measured the squeezing to be up to 0.3 dB below the vacuum noise from 50 MHz to 2 GHz limited by the measuring bandwidth of the homodyne detector. The squeezing strength was possibly limited by thermal lensing inside the non-linear crystal.
@article{arxiv.1201.5289,
title = {Continuous-wave non-classical light with GHz squeezing bandwidth},
author = {Stefan Ast and Aiko Samblowski and Moritz Mehmet and Sebastian Steinlechner and Tobias Eberle and Roman Schnabel},
journal= {arXiv preprint arXiv:1201.5289},
year = {2013}
}