# Experimental replication of single-qubit quantum phase gates

## TL;DR

This paper experimentally demonstrates a superreplication protocol for quantum phase gates using linear optics, achieving up to two high-fidelity replicas from a single input, confirming theoretical predictions.

## Contribution

First experimental implementation of a superreplication protocol for single-qubit phase gates using linear optics and quantum Toffoli gates.

## Key findings

- Successful 1->2 replication of quantum phase gates
- High fidelity of replicated gates confirmed by quantum process tomography
- Experimental results agree well with theoretical models

## Abstract

We experimentally demonstrate the underlying physical mechanism of the recently proposed protocol for superreplication of quantum phase gates [W. D\"ur, P. Sekatski, and M. Skotiniotis, Phys. Rev. Lett. 114, 120503 (2015)], which allows to produce up to $N^2$ high-fidelity replicas from N input copies in the limit of large N. Our implementation of 1->2 replication of the single-qubit phase gates is based on linear optics and qubits encoded into states of single photons. We employ the quantum Toffoli gate to imprint information about the structure of an input two-qubit state onto an auxiliary qubit, apply the replicated operation to the auxiliary qubit, and then disentangle the auxiliary qubit from the other qubits by a suitable quantum measurement. We characterize the replication protocol by full quantum process tomography and observe good agreement of the experimental results with theory.