The simulation of open quantum dynamics has recently allowed the direct investigation of the features of system-environment interaction and of their consequences on the evolution of a quantum system. Such interaction threatens the quantum properties of the system, spoiling them and causing the phenomenon of decoherence. Sometimes however a coherent exchange of information takes place between system and environment, memory effects arise and the dynamics of the system becomes non-Markovian. Here we report the experimental realisation of a non-Markovian process where system and environment are coupled through a simulated transverse Ising model. By engineering the evolution in a photonic quantum simulator, we demonstrate the role played by system-environment correlations in the emergence of memory effects.

Many future quantum technologies rely on the generation of entangled states. Quantum devices will require verification of their operation below some error threshold, but the reliable detection of quantum entanglement remains a considerable challenge for large-scale quantum systems. Well-established techniques for this task rely on the measurement of expectation values of entanglement witnesses, which however require many measurements settings to be extracted. Here we develop a generic framework for efficient entanglement detection that translates any entanglement witness into a resource-efficient probabilistic scheme, whose confidence grows exponentially with the number of individual detection events, namely copies of the quantum state. To benchmark our findings, we experimentally verify the presence of entanglement in a photonic six-qubit cluster state generated using three single-photon sources operating at telecommunication wavelengths. We find that the presence of entanglement can be certified with at least 99:74% confidence by detecting 20 copies of the quantum state. Additionally, we show that genuine six-qubit entanglement is verified with at least 99% confidence by using 112 copies of the state. Our protocol can be carried out with a remarkably low number of copies and in the presence of experimental imperfections, making it a practical and applicable method to verify large-scale quantum devices.

Blind quantum computing allows for secure cloud networks of quasi-classical clients and a fullyfledged quantum server. Recently, a new protocol has been proposed, which requires a client to perform only measurements. We demonstrate a proof-of-principle implementation of this measurement-only blind quantum computing, exploiting a photonic setup to generate four-qubit cluster states for computation and verification. Feasible technological requirements for the client and the device-independent blindness make this scheme very applicable for future secure quantum networks.

We report the experimental demonstration of two quantum networking protocols, namely quantum 1→3 telecloning and open-destination teleportation, implemented using a four-qubit register whose state is encoded in a high-quality two-photon hyperentangled Dicke state. The state resource is characterized using criteria based on multipartite entanglement witnesses. We explore the characteristic entanglement-sharing structure of a Dicke state by implementing high-fidelity projections of the four-qubit resource onto lower-dimensional states. Our work demonstrates for the first time the usefulness of Dicke states for quantum information processing. PACS numbers: 42.50.Dv,03.67.Bg,42.50.Ex Networking offers the benefits of connectivity and sharing, often allowing for tasks that individuals are unable to accomplish on their own. This is known for computing, where grids of processors outperform the computational power of single machines or allow the storage of much larger databases. It should thus be expected that similar advantages are transferred to the realm of quantum information. Quantum networking, where a given task is pursued by a lattice of local nodes sharing (possibly entangled) quantum channels, is emerging as a realistic scenario for the implementation of quantum protocols requiring medium/large registers. Key examples of such approach are given by quantum repeaters [1], non-local gates [2], scheme for light-mediated interactions of distant matter qubits [3] and one-way quantum computation [4].In this scenario, photonics is playing an important role: the high reconfigurability of photonic setups and outstanding technical improvements have facilitated the birth of a new generation of experiments (performed both in bulk optics and, recently, in integrated photonic circuits [5]) that have demonstrated multi-photon quantum control towards high-fidelity computing with registers of a size inaccessible until only recently [6][7][8][9][10][11]. The design of complex interferometers and the exploitation of multiple degrees of freedom of a single photonic information carrier have enabled the production of interesting states, such as cluster/graph states, GHZ-like states and (phased) Dicke states [12][13][14], among others [15,16]. Dicke states have been successfully used to characterize multipartite entanglement close to fully symmetric states and its robustness to decoherence [14]. They are potentially useful resource for the implementation of protocols for distributed quantum communication such as quantum secret sharing [17], quantum telecloning (QTC) [18], and open destination teleportation (ODT) [19,20]. So far, such opportunities have only been examined theoretically and confirmed indirectly [12,13], leaving a full implementation of such protocols unaddressed.In this Letter, we report the experimental demonstration of 1→ 3 QTC and ODT of logical states using a four-qubit symmetric Dicke state with two excitations realized using a highquality hyperentangled (HE) photonic resource [14,21]. The entanglement-sharing ...