# Time-bin and Polarization Superdense Teleportation for Space Applications

## TL;DR

This paper demonstrates a high-fidelity superdense teleportation system using hyperentangled photons suitable for space-based quantum communication, including Doppler shift compensation for satellite links.

## Contribution

It introduces a hyperentangled photon system capable of superdense teleportation with high fidelity and phase resolution, and demonstrates Doppler shift compensation for satellite communication.

## Key findings

- Achieved an average fidelity of 0.94 in superdense teleportation.
- Demonstrated Doppler shift compensation for satellite links.
- Sufficient coincidence counts for single-pass state reconstruction.

## Abstract

To build a global quantum communication network, low-transmission, fiber-based communication channels can be supplemented by using a free-space channel between a satellite and a ground station on Earth. We have constructed a system that generates hyperentangled photonic "ququarts" and measures them to execute multiple quantum communication protocols of interest. We have successfully executed and characterized superdense teleportation, a modified remote-state preparation protocol that transfers more quantum information than standard teleportation, for the same classical information cost, and moreover, is in principle deterministic. Our measurements show an average fidelity of $0.94\pm0.02$, with a phase resolution of $\sim7^{\circ}$, allowing reliable transmission of $>10^5$ distinguishable quantum states. Additionally, we have demonstrated the ability to compensate for the Doppler shift, which would otherwise prevent sending time-bin encoded states from a rapidly moving satellite, thus allowing the low-error execution of phase-sensitive protocols during an orbital pass. Finally, we show that the estimated number of received coincidence counts in a realistic implementation is sufficient to enable faithful reconstruction of the received state in a single pass.