Implementation of quantum repeater scheme based on non-identical quantum memories

Quantum key distribution aims to distribute a secret key among distant parties linked by an optical fiber or free space. Unfortunately, the main problem which limits the long distance direct transmission of qubits is the exponential decay of the signal. This limit can be overcome by introducing quantum repeaters (QRs) between the two distant points. Quantum repeaters suggest a technique for establishing long distance quantum communication by the construction of entangled qubits among the end point of the channel, by dividing the channel into elementary links edged with quantum memory (QM) called nodes. Many schemes use identical QMs (Mastromattei in Assessing the practicality of a simple multi-node quantum repeater. M.Sc. thesis, University of Waterloo, ON, Canada, 2017). These schemes need QMs of long life times and high efficiencies which is not the practical case for QMs. To optimize these requirements, a multi-node sequential quantum repeater of a non-identical QMs is proposed here to interplay between the total channel efficiency and decoherence time T₂ and the quantum memories life times and their efficiencies to enhance the execution of the quantum repeater (QR). The outcomes show that the interplay between the decoherence time and efficiency in non-identical QR improves the key rate as compared to that of the identical QR, the distance of the channel can be extended by using non-identical QMs repeater scheme since quantum bit error rate is decreased, and the cost of fabricating non-identical QMs repeater is reduced since we use most QMs with low life time.