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Figure 2 | EPJ Quantum Technology

Figure 2

From: CubeSat quantum communications mission

Figure 2

Concept of Operations for CQuCoM. The CQuCoM 6U CubeSat would be deployed from the ISS into a circular low-Earth orbit. The ground track includes the Matera Laser Rangefinding Observatory operated by the University of Padua that would act as the optical ground station (OGS). The OGS would transmit a strong guide beacon at 532 nm allowing the CQuCoM CubeSat to acquire and begin tracking the target position. Rotating the entire satellite to point towards the OGS provides coarse pointing to sub-degree level, sufficient to bring the OGS beacon within the acquisition field of view of the beacon tracking sensor. The beacon tracker is co-aligned with the outgoing signal photons and allows precision determination of the transmit telescope boresight direction. The error signal from the beacon tracker is used to drive a fast-steering mirror to direct signal photons to the OGS. The fine-pointing system takes into account the velocity aberration with point-ahead correction. A quantum source on board the satellite provides single-photon level signals that are detected by the OGS. A switchable strong/weak coherent pulse source allows both the possibility of characterization of pointing performance and the free-space channel as well as quantum key distribution. An entangled-photon source would allow the distribution of entanglement between space and ground, one of the photon-pair is measured onboard and the results are compared with its respective partner detected on the ground.

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