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.

We present a novel optical device based on an integrated system of micro-lenses and single mode optical fibers. It allows to collect and direct into many modes two photons generated by spontaneous parametric down conversion. By this device multiqubit entangled states and/or multilevel qu-dit states of two photons, encoded in the longitudinal momentum degree of freedom, are created. The multi-path photon entanglement realized by this device is expected to find important applications in modern quantum information technology. Entangling two photons in a high-dimension Hilbert space allows the realization of important quantum information tasks. These deal with a complete analysis of Bell states [1,2,3] and novel protocols of superdense coding [4], the possibility to perform secure quantum cryptography [5,6] and a fast, high-fidelity one-way quantum computation [7], [8,9,10,11], besides the realization of novel quantum nonlocality tests [12,13,14,15].Multidimensional entangled states of two photons have been realized by engineering both qu-dit states and hyperentangled (HE) states. In the former each particle belongs to a d-level quantum system, in the latter the particles are entangled in more than one degree of freedom (DOF). Since a qu-dit, with d = 2 N , is equivalent to N qubits, two-entangled qu-dits are equivalent to the HE state of two particles entangled in N DOFs. Polarization, time bin and spatial entanglement have been adopted to create qu-dits with d = 3 [6,16], d = 4 [17] and d = 8 [18]. At the same time, HE states have been realized by using in different ways polarization, longitudinal momentum and orbital angular momentum, besides time-bin entanglement [1,19,20,21,22].In this paper we present the first experimental realization of a quantum state of two photons entangled in many optical paths. It is based on the spontaneous parametric down conversion (SPDC) emission of a Type I phase-matched nonlinear (NL) crystal operating under the excitation of a continuous wave (cw) laser at wavelength (wl) λ p . In these conditions, the degenerate signal (s) and idler (i) photons, are generated with uniform probability distribution, at wl λ s = λ i = 2λ p , over a continuum of correlated k-modes belonging to the lateral surface of a cone. Usually, no more than two correlated spatial modes are used in experiments based on Type I crystals, hence the main part of SPDC radiation is lost. By exploiting the continuum of k-mode emission of Type * URL: http://quantumoptics.phys.uniroma1.it/ I crystals, high-dimension entangled states can be created [23]. Indeed, a very large number of qubits are in principle available by this geometry. However, a successfull realization of this idea strongly depends on the possibility to overcome the practical difficulties represented by independently collecting and manipulating the SPDC radiation belonging to a large number of k-modes.By the device realized in this experiment, photon pairs travelling along a large number of k-modes are efficiently coupled into a bundle of single mode opt...

Quantum mechanics is a nonlocal theory, but not as nonlocal as the no-signalling principle allows. However, there exist quantum correlations that exhibit maximal nonlocality: they are as nonlocal as any nonsignalling correlation and thus have a local content, quantified by the fraction p(L) of events admitting a local description, equal to zero. We exploit the known link between the Kochen-Specker and Bell theorems to derive a maximal violation of a Bell inequality from every Kochen-Specker proof. We then show that these Bell inequalities lead to experimental bounds on the local content of quantum correlations that are significantly better than those based on other constructions. We perform the experimental demonstration of a Bell test originating from the Peres-Mermin Kochen-Specker proof, providing an upper bound on the local content pL less than or similar to 0.22

We report on an experimental violation of the Bell-Clauser-Horne-Shimony-Holt (Bell-CHSH) inequality using energy-time-entangled photons. The experiment is not free of the locality and detection loopholes but is the first violation of the Bell-CHSH inequality using energy-time entangled photons which is free of the postselection loophole described by Aerts et al. [Phys. Rev. Lett. 83, 2872 (1999)]

A recently introduced family of multipartite entangled states, the 4-qubit phased Dicke states, has been created by 2-photon hyperentanglement. Our experimental method allows high state fidelity and generation rate. By introducing quantum noise in the multipartite system in a controlled way, we have tested the robustness of these states. To this purpose the entanglement of the resulting multipartite entangled mixed states has been verified by using a new kind of structural witness.

We present the experimental realization of the optimal estimation protocol for a Pauli noisy channel. The method is based on the generation of 2-qubit Bell states and the introduction of quantum noise in a controlled way on one of the state subsystems. The efficiency of the optimal estimation, achieved by a Bell measurement, is shown to outperform quantum process tomography.

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 ...

We experimentally demonstrate the achievement of the entanglement-assisted capacity for classical information transmission over a depolarizing channel. The implementation is based on the generation and local manipulation of two-qubit Bell states, which are finally measured at the receiver by realizing projective measurements in the Bell basis. The depolarizing channel is realized by introducing quantum noise in a controlled way on one of the two qubits. This work represents an investigation into the amount of information that can be shared in the presence of noise. DOI: 10.1103/PhysRevA.87.02233