Experimental optimal cloning of four-dimensional quantum states of photons

TL;DR

This paper demonstrates the first experimental optimal cloning of four-dimensional quantum states (ququarts) encoded in photon properties, showing scalability and general applicability to higher-dimensional quantum states and multiple copies.

Contribution

It presents the first experimental realization of optimal quantum cloning for four-dimensional states and introduces a scalable, general method applicable to higher-dimensional quantum systems.

Findings

Successful cloning of four-dimensional quantum states with high fidelity

Method applicable to quantum states of arbitrary high dimension

Scalable to multiple copies and higher dimensions

Abstract

Optimal quantum cloning is the process of making one or more copies of an arbitrary unknown input quantum state with the highest possible fidelity. All reported demonstrations of quantum cloning have so far been limited to copying two-dimensional quantum states, or qubits. We report the experimental realization of the optimal quantum cloning of four-dimensional quantum states, or ququarts, encoded in the polarization and orbital angular momentum degrees of freedom of photons. Our procedure, based on the symmetrization method, is also shown to be generally applicable to quantum states of arbitrarily high dimension -- or qudits -- and to be scalable to an arbitrary number of copies, in all cases remaining optimal. Furthermore, we report the bosonic coalescence of two single-particle entangled states.