Quantum Cloning without Interference

TL;DR

This paper demonstrates that quantum cloning with optimal fidelity can be achieved without interference, challenging the traditional view that interference is essential for quantum advantage in cloning tasks.

Contribution

The paper introduces a class of interference-free quantum cloners that reach optimal fidelity, expanding understanding of quantum cloning mechanisms.

Findings

Interference is not necessary for optimal quantum cloning.

A class of symmetric universal 1→2 qubit cloners achieves fidelity 5/6 without interference.

Optimal asymmetric interference-free cloners are also identified.

Abstract

We study the role of interference in the process of quantum cloning. We show that in order to achieve better than classical cloning of a qubit no interference is needed. In particular, a large class of symmetric universal 1$\to$ 2 qubit cloners exists which achieve the optimal average fidelity 5/6 for such machines, without using any interference. We also obtain optimal average fidelities for interference--free cloning in asymmetric situations, and discuss the relation of the quantum cloners found to the Bu\v{z}ek--Hillery quantum cloner.