Structure of multipartite entanglement in random cluster-like photonic systems

Quantum networks are natural scenarios for the communication of information among distributed parties, and the arena of promising schemes for distributed quantum computation. Measurement-based quantum computing is a prominent example of how quantum networking, embodied by the generation of a special class of multipartite states called cluster states, can be used to achieve a powerful paradigm for quantum information processing. Here we analyze randomly generated cluster states in order to address the emergence of multipartite correlations as a function of the density of edges in a given underlying graph. We find that the most widespread multipartite entanglement does not correspond to the highest amount of edges in the cluster. We extend the analysis to higher dimensions, finding similar results, which suggest the establishment of small world structures in the entanglement sharing of randomised cluster states, which can be exploited in engineering more efficient quantum information carriers.Comment: 6 pages, 8 figures, revtex4-

Exploiting path-polarization hyperentangled photons for multiqubit quantum information protocols

In this thesis we describe and exploit a photonic source of hyperentangled states which allows the creation of a four qubit entangled state using path and polarization of two photons; this will be the main resource for a series of experiments that are linked to the main goal of exploring the advantages that quantum correlations brings in the aforementioned tasks. In particular we will focus onto showing that the same correlations which define the \emph{quantumness} of a state can be interpreted in two very different ways: either as something that introduces \emph{non-locality} between qubits, or something which reduces the \emph{information entropy} between qubits. Both interpretations allow the definition and observation of quantum advantage but, as we will show, the two views are not completely equivalent. Our goal will be showing that quantum correlations can be seen as \emph{currency} that can be spent to perform tasks more efficiently than in the classical case

Stimulated Emission Tomography: Beyond Polarization

In this work we demonstrate the use of stimulated emission tomography to characterize a hyper-entangled state generated by spontaneous parametric down-conversion in a CW-pumped source. In particular, we consider the generation of hyper-entangled states consisting of photon pairs entangled in polarisation and path. These results extend the capability of stimulated emission tomography beyond the polarisation degree of freedom, and demonstrate the use of this technique to study states in higher dimension Hilbert spaces

Experimental detection of quantum channel capacities

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 $\sigma_{z}\otimes\sigma_{z}$.Comment: 5 pages and 3 figures in the principal article, and 4 pages in the supplementary materia

Hyperentangled photon states on a chip

In order to achieve an optimal scalability, stability and compactness of complex quantum optical schemes based on a large number of elements, waveguide technology is of fundamental importance. Lately this technique has been implemented with experimental success with the introduction in the quantum domain of photonic integrated circuits built in various platforms and materials [1