Entanglement-based QKD for Space Applications
In 2016, the maiden satellite featuring a dedicated quantum payload, Micius, was successfully launched as part of the QUESS mission led by the Chinese Academy of Sciences. This mission showcased various quantum communication protocols via satellite links, including satellite-relayed QKD, satellite-to-ground QKD, and entanglement-based QKD via a dual downlink. Other missions have also deployed dedicated satellite transmitter payloads, fueling the development of robust quantum technologies.
The polarization domain has emerged as the preferred photonic property for encoding quantum states over free-space links. This is due to its resilience in free-space propagation, availability of high-quality polarization-encoded photon sources, and efficient compact receiving modules. The adoption of entanglement-based QKD protocols offers two significant advantages for space applications. Unlike prepare-and-measure protocols, entanglement-based schemes allow a malicious party to possess the source of entangled photon pairs, as eavesdropping attempts are detectable through measurement outcome correlations. This attribute is especially relevant for space-based quantum cryptography, considering that trust in cryptographic devices is not always guaranteed in QKD implementations.
The Micius satellite successfully distributed a secure key rate of 0.12 bits/s via a dual downlink between ground parties separated by 1120 km. Despite this achievement, the commercial viability of QKD depends on costs per secret bit. The existing hardware on satellites and ground stations is already operating near optimum levels, leaving limited room for further optimization. Commercial feasibility requires innovative approaches to increase secure key rates and reduce costs per secret bit. The inherent quantum correlations of entanglement-based QKD protocols offer avenues for achieving these goals.
While quantum repeaters are relatively immature regarding technology readiness, integrated photon-pair sources can enhance key rates and decrease power consumption. Adaptive optics, crucial for linking fiber-based quantum networks with satellite-based ones, adds complexity to the ground receiver. Multiplexed and high-dimensional QKD appear promising avenues for increasing key rates, requiring changes primarily to ground receivers, with a more versatile space segment in entanglement-based scenarios.
The lengthy timeline of space missions underscores the importance of early identification of potential technologies for future QKD missions. Advancements in this realm should be embraced to enhance quantum cryptography capabilities and foster the development of the quantum internet. Ultimately, progress in entanglement-based QKD in space strengthens quantum cryptography and propels quantum internet development.
References —
Note: This article is a part of my Womanium Online Quantum Media Project. Find out about it here .
#WomaniumQuantum #Quantum30 #QCI