Experimental detection of quantum channel capacities

TL;DR

This paper introduces an efficient experimental method to certify non-zero quantum channel capacities using entangled photons and minimal measurements, avoiding full process tomography.

Contribution

The authors develop a practical procedure to estimate lower bounds of quantum capacities with simple local measurements on entangled photon pairs, bypassing complex tomography.

Findings

Successfully certifies non-zero quantum capacities experimentally.

Uses only three local measurements to estimate entropy bounds.

Applicable to unknown noisy quantum channels.

Abstract

We present an effcient experimental procedure that certifies non vanishing quantum capacities for qubit noisy channels. Our method is based on the use of a fixed bipartite entangled state, where the system qubit is sent to the channel input. A particular set of local measurements is performed at the channel output and the ancilla qubit mode, obtaining lower bounds to the quantum capacities for any unknown channel with no need of a quantum process tomography. The entangled qubits have a Bell state configuration and are encoded in photon polarization. The lower bounds are found by estimating the Shannon and von Neumann entropies at the output using an optimized basis, whose statistics is obtained by measuring only the three observables $\sigma_{x}\otimes\sigma_{x}$, $\sigma_{y}\otimes\sigma_{y}$ and $\sigma_{z}\otimes\sigma_{z}$.