“Architectures for long distance quantum communication”
Despite the tremendous progress of quantum cryptography, efficient quantum communication over long distances (> 1000 km) remains an outstanding challenge due to fiber attenuation and operation errors accumulated over the entire communication distance. Quantum repeaters (QRs), as a promising approach, can overcome both photon loss and operation errors, and hence significantly speedup the communication rate. Depending on the methods used to correct loss and operation errors, all the proposed QR schemes can be classified into three categories (generations). The first generation QRs uses heralded entanglement generation for the correction of erasure errors and entanglement purification for the correction of operation errors. The second generation QRs uses heralded entanglement generation for the correction of erasure errors and quantum error correction for the correction of operation errors. The third generation QRs uses quantum error correction for the correction of both erasure and operation errors respectively. It is important to develop robust protocols for quantum repeaters, and systematically compare the performance of various QRs.
We investigate the usage of efficient error correcting codes for third generation QRs that makes use of small encoding blocks to fault-tolerantly correct both loss and operation errors. Our schemes use quantum parity codes, quantum polynomial codes and quantum Reed-Solomon codes for encoding quantum information and use teleportation based error correction to systematically correct erasure and operation errors in a fault tolerant manner. We describe a way to optimize the resource requirements and system parameters for these QRs with the aim of generating a secure key. We perform a systematic comparison between these codes and identify the parameter regimes of operation errors where each code performs the best.
We then perform a systematic comparison of three generations of QRs by evaluating the cost of both temporal and physical resources, and identify the optimized QR architecture for a given set of experimental parameters. Our work provides a roadmap for the experimental realizations of highly efficient quantum networks over transcontinental distances.