Free-Space Quantum Key Distribution using Polarization Entangled Photons

Guangyu Zhang, Siyu Song, Junlin Li +2 more

Onur Kuzucu, Franco N. C. Wong

We demonstrate a narrowband pulsed source of polarization-entangled photons based on parametric downconversion in a phase-stable Sagnac interferometer that is suitable for free-space quantum key distribution with high key generation rates.

Israel J. Owens

Ramy Tannous

Free-space quantum key distribution has recently achieved several milestones, such as \nthe launch and results of the first quantum satellite, Micius. The emergence of quantum satellites has certainly made progress towards the realization of a global quantum cryptographic network. In this thesis, two challenges in the development of an optical quantum ground station \nfor a free-space quantum satellite link are studied. The first is the development of a high brightness, fiber pigtailed waveguide that is to be used as a polarization entangled photon source. The high pair production rate is required in order to meet the requirements for a satellite up-link configuration. The portability, robustness and ease of alignment were motivations for choosing a fiber pigtailed source. Certain challenges that are fundamental to the source design were characterized and several solutions to these challenges were investigated. The other main investigation in this thesis, is the development of a passive polarization \ncompensation using polarization maintaining fibers. The birefringence in standard single mode optical fibers causes random polarization rotations to the light passing through the fiber. Polarization maintaining fibers, though very high in birefringence, are used with entangled photons and techniques from reference frame independent quantum key distribution protocols are shown to compensate for random polarization rotations while preserving the entanglement. In addition, the feasibility of the protocol using the polarization maintaining fibers is investigated. \nThrough various studies, experiments, and component design, the feasibility of a pigtailed waveguide entangled photon source has been shown to need further investigation, while the feasibility of implementing polarization maintaining fibers to the ground station has been shown to be effective. It is particularly effective as a passive polarization compensation system that uses entanglement, however a similar concept is effective for non-entangled single photons. This work contributes to a long line of achievements leading towards satellite implementations of quantum key distribution for an eventual global quantum cryptographic network.

Gregor Weihs

Zheng Kai

This paper analyzes several protocols for quantum key distribution based on single photon, summarizes the research status on theory and experiment based on photon polarization state and entangled state, illustrate the challenge of the free-space quantum key distribution, and finally advances the problems and future of global quantum communication.