Gaussian entanglement distribution with GHz bandwidth
S. Ast, Melanie Ast, Moritz Mehmet, Roman Schnabel · arXiv (Cornell University) · 2016
The distribution of Gaussian entanglement can be used to generate a mathematically-proven secure key for quantum cryptography. The distributed secret key rate is limited by the bandwidth of the nonlinear resonators used for entanglement generation, which is less than 100 MHz for current state-of-the-art setups. The development of an entanglement source with a higher bandwidth promises an increased measurement speed and a linear boost in the secure data rate. Here, we present the experimental realization of a continuous-variable entanglement source with a bandwidth of more than 1.25 GHz. The measured entanglement spectrum was quantified via the inseparability criterion introduced by Duan and coworkers with a critical value of 4 below which entanglement is certified. The measurements yielded an inseparability value of about 1.8 at a frequency of 300 MHz to about 2.8 at 1.2 GHz extending further to about 3.1 at 1.48 GHz. In the experiment we used two 2.6 mm long monolithic PPKTP crystal resonators to generate two squeezed fields at the telecommunication wavelength of 1550 nm. The experimentally achieved entanglement strength was mainly limited by the total optical detection efficiency of 59% in the set-up as well as by the injected pump power of the nonlinear process for the entanglement generation.