# Interstellar communication. I. Maximized data rate for lightweight space-probes

## TL;DR

This paper derives the optimal quantum communication scheme for lightweight interstellar probes, achieving data rates of about bits per second per Watt over interstellar distances using advanced photon suppression and wavelength optimization.

## Contribution

It introduces a quantum information framework to maximize data rates from minimal instrumentation interstellar probes, considering realistic noise and technological constraints.

## Key findings

- Maximum data rate of a few bits per second per Watt at 1.3 parsecs.
- Optimal wavelength range is 300-400 nm for interstellar distances.
- Data capacity is limited by quantum bounds and noise sources.

## Abstract

Recent technological advances could make interstellar travel possible, using ultra-lightweight sails pushed by lasers or solar photon pressure, at speeds of a few percent the speed of light. Obtaining remote observational data from such probes is not trivial because of their minimal instrumentation (gram scale) and large distances (pc). We derive the optimal communication scheme to maximize the data rate between a remote probe and home-base. he framework requires coronagraphic suppression of the stellar background at the level of $10^{-9}$ within a few tenths of an arcsecond of the bright star. Our work includes models for the loss of photons from diffraction, technological limitations, interstellar extinction, and atmospheric transmission. Major noise sources are atmospheric, zodiacal, stellar and instrumental. We examine the maximum capacity using the "Holevo bound" which gives an upper limit to the amount of information (bits) that can be encoded through a quantum state (photons), which is a few bits per photon for optimistic signal and noise levels. This allows for data rates of order bits per second per Watt from a transmitter of size 1 m at a distance of $\alpha\,$Centauri (1.3 pc) to an earth-based large receiving telescope (E-ELT, 39 m). The optimal wavelength for this distance is 300 nm (space-based receiver) to 400 nm (earth-based) and increases with distance, due to extinction, to a maximum of $\approx3\,\mu$m to the center of the galaxy at 8 kpc.