Fiber distribution of phase-stabilized GHz-bandwidth squeezed vacuum states of light between two buildings

One-sided device-independent Quantum Key Distribution (QKD) targets a mathematically proven secure communication between two parties without the need to trust the devices on one side. An appealing kind of high-speed implementation uses GHz-bandwidth two-mode squeezed states, distributed via an optical fiber link. The remote measurements, however, require the precise control of the phase with respect to an optical homodyne local oscillator. Here, we report what is believed to be the first transmission of single-mode squeezed vacuum states with GHz bandwidth over a 1 km optical fiber into a neighboring building combined with phase-stabilized measurements. We directly measure a squeeze factor of up to 4 dB. Our result is an important step towards high-speed QKD with enhanced security level for km-scale areas, e.g., government districts.