Sequential quantum cloning under real-life conditions

TL;DR

This paper presents a practical method for implementing optimal quantum cloning sequentially, using matrix-product states and variational optimization, significantly reducing resource requirements and enabling feasible experimental realization.

Contribution

It introduces an optimized sequential quantum cloning protocol leveraging MPS formalism, reducing ancilla dimension and resource use compared to prior approaches.

Findings

Achieves sequential cloning with ancilla dimension D ≤ 3 for up to 15 qubits.

Demonstrates significant resource savings over previous linear scaling predictions.

Provides a realistic framework for experimental implementation of optimal quantum cloning.

Abstract

We consider a sequential implementation of the optimal quantum cloning machine of Gisin and Massar and propose optimization protocols for experimental realization of such a quantum cloner subject to the real-life restrictions. We demonstrate how exploiting the matrix-product state (MPS) formalism and the ensuing variational optimization techniques reveals the intriguing algebraic structure of the Gisin-Massar output of the cloning procedure and brings about significant improvements to the optimality of the sequential cloning prescription of Delgado et al [Phys. Rev. Lett. 98, 150502 (2007)]. Our numerical results show that the orthodox paradigm of optimal quantum cloning can in practice be realized in a much more economical manner by utilizing a considerably lesser amount of informational and numerical resources than hitherto estimated. Instead of the previously predicted linear scaling of the required ancilla dimension D with the number of qubits n, our recipe allows a realization of such a sequential cloning setup with an experimentally manageable ancilla of dimension at most D=3 up to n=15 qubits. We also address satisfactorily the possibility of providing an optimal range of sequential ancilla-qubit interactions for optimal cloning of arbitrary states under realistic experimental circumstances when only a restricted class of such bipartite interactions can be engineered in practice.