Experimental demonstration of entanglement-enabled universal quantum cloning in a circuit

TL;DR

This paper demonstrates a universal quantum cloning machine in a superconducting circuit, revealing entanglement-based correlations that are independent of input states, enabling deterministic and individual cloning of qubits.

Contribution

First experimental realization of a deterministic, individual universal quantum cloning machine in a superconducting circuit, highlighting entanglement-based universality.

Findings

Measured entanglements match theoretical predictions

Entanglements are input-state independent

Achieved deterministic, individual cloning

Abstract

No-cloning theorem forbids perfect cloning of an unknown quantum state. A universal quantum cloning machine (UQCM), capable of producing two copies of any input qubit with the optimal fidelity, is of fundamental interest and has applications in quantum information processing. This is enabled by delicately tailored nonclassical correlations between the input qubit and the copying qubits, which distinguish the UQCM from a classical counterpart, but whose experimental demonstrations are still lacking. We here implement the UQCM in a superconducting circuit, and investigate these correlations. The measured entanglements well agree with our theoretical prediction that they are independent of the input state and thus constitute a universal quantum behavior of the UQCM that was not previously revealed. Another feature of our experiment is the realization of deterministic and individual cloning, in contrast to previously demonstrated UQCMs, which either were probabilistic or did not constitute true cloning of individual qubits.