Gaussian entanglement distribution with gigahertz bandwidth

TL;DR

This paper reports the experimental creation of a high-bandwidth Gaussian entanglement source exceeding 1.25 GHz, demonstrating strong continuous-variable entanglement suitable for fast quantum cryptography.

Contribution

It presents the first realization of a gigahertz-bandwidth Gaussian entanglement source using PPKTP resonators, enabling faster quantum communication.

Findings

Achieved entanglement bandwidth over 1.25 GHz.

Measured inseparability values indicating strong entanglement.

Demonstrated detection of high-speed continuous-variable entanglement.

Abstract

The distribution of entanglement with Gaussian statistic can be used to generate a mathematically-proven secure key for quantum cryptography. The distributed secret key rate is limited by the {entanglement strength, the entanglement bandwidth and the bandwidth of the photo-electric detectors}. The development of a source for strongly, bi-partite entangled light with high bandwidth promises an increased measurement speed and a linear boost in the secure data rate. Here, we present the experimental realization of a Gaussian entanglement source with a bandwidth of more than 1.25\,GHz. The entanglement spectrum was measured with balanced homodyne detectors and was quantified via the inseparability criterion introduced by Duan and coworkers with a critical value of 4 below which entanglement is certified. Our 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 periodically poled potassium titanyl phosphate (PPKTP) resonators to generate two squeezed fields at the telecommunication wavelength of 1550\,nm. Our result proves the possibility of generating and detecting strong continuous-variable entanglement with high speed.