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). 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.
We will specifically look at the experimental system of two species ion traps for the realization of a specific architecture for quantum repeaters. Two-species trapped ions with one memory qubit and one communication qubit provides a promising platform for the realization of quantum repeaters and future quantum networks. We analyze quantum repeater architecture based on two-species trapped ions using Yb ion as a memory qubit and Ba ion as communication qubit in the context of long-distance quantum key distribution. Optimization of swapping operation between memory and communication qubits and overcoming the single-shot measurement limitation of the communication qubit is considered. We examine the maximal achievable rates for various quantum repeater architectures using two-species trapped ions as building blocks. We derive the dependence of the quantum key distribution rate on coupling efficiency, gate infidelity, operation time and length of the elementary links.