Q³Sat: Quantum Communications Uplink to a 3U CubeSat – Feasibility & Design

Introduction In the absence of technically mature quantum repeaters, losses in optical fibers limit the distance for ground-bound quantum key distribution. One way to overcome these losses is via optical links to satellites,... [ view full abstract ]

Introduction

In the absence of technically mature quantum repeaters, losses in optical fibers limit the distance for ground-bound quantum key distribution. One way to overcome these losses is via optical links to satellites, which has been demonstrated in course of the Chinese-Austrian QUESS mission. Though its findings were impressive, such a large-scale project requires massive financial and time resources. We propose a 34x10x10cm³ nanosatellite according to the CubeSat standard which is able to perform quantum key distribution (QKD) at a fraction of the cost. Our Q³Sat mission design incorporates an uplink and trusted-node scenario, using only commercially available components. 

Methods

We have performed a detailed analysis of suitable QKD protocols, ground-based sources, possible orbits, weather considerations, optical (geometric and absorption) losses, pointing stability, noise counts, detector performance, clock synchronization, temporal stability, classical communication and computing requirements to arrive at a link budget which we can use to calculate the expected quantum secure key rates. We have also created a preliminary design of such a 3U CubeSat including a detailed size, weight and power budget and a CAD to account for the assembly of the components.

Results

Our calculations show that a 3U CubeSat consisting of a mirror telescope unit, an optical analysis unit and a housekeeping / communication unit could be used as a quantum receiver in an uplink configuration. For one such CubeSat, we estimate the quantum secure key to be acquired between two ground stations during one year to be about 13 Mbit when deploying a decoy protocol. A Bell test between ground and satellite would also be feasible

Discussion

The uplink design allows to keep the more sensitive, computation-intensive and expensive devices on ground. The experiment proposed by us therefore poses a comparably low-threshold quantum space mission. For a two-year lifetime of the satellite, the price per kilobit would amount to about 20 Euro. In large constellations, Q³Sats could be used to establish a global quantum network, which would further lower the cost. Summarizing, our detailed design and feasibility study can be readily used as a template for global-scale quantum communication.