Experimental bilocality violation without shared reference frames

Non-classical correlations arising in complex quantum networks are attracting growing interest, both from a fundamental perspective and for potential applications in information processing. In particular, in an entanglement swapping scenario a new kind of correlations arise, the so-called nonbilocal correlations that are incompatible with local realism augmented with the assumption that the sources of states used in the experiment are independent. In practice, however, bilocality tests impose strict constraints on the experimental setup and in particular to presence of shared reference frames between the parties. Here, we experimentally address this point showing that false positive nonbilocal quantum correlations can be observed even though the sources of states are independent. To overcome this problem, we propose and demonstrate a new scheme for the violation of bilocality that does not require shared reference frames and thus constitute an important building block for future investigations of quantum correlations in complex networks.Comment: 10 page

Maximal qubit violation of n-locality inequalities in a star-shaped quantum network

Bellʼs theorem was a cornerstone for our understanding of quantum theory and the establishment ofBell non-locality played a crucial role in the development of quantum information. Recently, itsextension to complex networks has been attracting growing attention, but a deep characterization ofquantum behavior is still missing for this novel context. In this work we analyze quantum correlationsarising in the bilocality scenario, that is a tripartite quantum network where the correlations betweenthe parties are mediated by two independent sources of states. First, we prove that non-bilocalcorrelations witnessed through a Bell-state measurement in the central node of the network form asubset of those obtainable by means of a local projective measurement. This leads us to derive themaximal violation of the bilocality inequality that can be achieved by arbitrary two-qubit quantumstates and arbitrary local projective measurements. We then analyze in details the relation between theviolation of the bilocality inequality and the CHSH inequality. Finally, we show how our method canbe extended to then-locality scenario consisting ofntwo-qubit quantum states distributed amongn1+nodes of a star-shaped networ

Experimental study of nonclassical teleportation beyond average fidelity

Quantum teleportation establishes a correspondence between an entangled state shared by two separate par- ties that can communicate classically and the presence of a quantum channel connecting the two parties. The standard benchmark for quantum teleportation, based on the average fidelity between the input and output states, indicates that some entangled states do not lead to channels which can be certified to be quantum. It was re- cently shown that if one considers a finer-tuned witness, then all entangled states can be certified to produce a non-classical teleportation channel. Here we experimentally demonstrate a complete characterization of a new family of such witnesses, of the type proposed in Phys. Rev. Lett. 119, 110501 (2017) under different con- ditions of noise. Furthermore, we show non-classical teleportation using quantum states that can not achieve average teleportation fidelity above the classical limit. Our results have fundamental implications in quantum information protocols and may also lead to new applications and quality certification of quantum technologies.Comment: 5 pages + Supp. Material

Experimental violation of local causality in a quantum network

Bell's theorem plays a crucial role in quantum information processing and thus several experimental investigations of Bell inequalities violations have been carried out over the years. Despite their fundamental relevance, however, previous experiments did not consider an ingredient of relevance for quantum networks: the fact that correlations between distant parties are mediated by several, typically independent sources. Here, using a photonic setup, we investigate a quantum network consisting of three spatially separated nodes whose correlations are mediated by two distinct sources. This scenario allows for the emergence of the so-called non-bilocal correlations, incompatible with any local model involving two independent hidden variables. We experimentally witness the emergence of this kind of quantum correlations by violating a Bell-like inequality under the fair-sampling assumption. Our results provide a proof-of-principle experiment of generalizations of Bell's theorem for networks, which could represent a potential resource for quantum communication protocols

Experimental bilocality violation without shared reference frames

Nonclassical correlations arising in complex quantum networks are attracting growing interest, both from afundamental perspective and for potential applications in information processing. In particular, in an entanglementswapping scenario a new kind of correlations arise, the so-called nonbilocal correlations that are incompatible withlocal realism augmented with the assumption that the sources of states used in the experiment are independent.In practice, however, bilocality tests impose strict constraints on the experimental setup and in particular to thepresence of shared reference frames between the parties. Here, we experimentally address this point showing thatfalse positive nonbilocal quantum correlations can be observed even though the sources of states are independent.To overcome this problem, we propose and demonstrate a scheme for the violation of bilocality that does notrequire shared reference frames and thus constitutes an important building block for future investigations ofquantum correlations in complex network

Optical detection of different phenolic compounds by means of a novel biosensor based on sol-gel immobilized laccase

A novel sol-gel based biosensor exploiting the optical absorption properties of sol-gel immobilized laccase has been constructed in the attempt to increase enzyme specificity towards different phenolic substrates. Laccase from Trametes versicolor has been immobilized in optically transparent sol-gel matrices. Using Fourier transform infrared spectroscopy and data analysis based on a wavelet algorithm the successful enzyme immobilization has been evidenced. The changes in the optical absorption spectra of laccase reaction products at 425 nm, 375 nm and 400 nm have been used for hydroquinone, resorcinol and catechol concentration determination, respectively. Due to the slow response time of hydroquinone-laccase reaction, our optical biosensor has been tested with resorcinol and catechol. Linear ranges up to 1.4 mM and 0.2 mM, limit-of-detection (LOD) of 4.5 μM and 0.6 μΜ have been evidenced for resorcinol and catechol, respectively. Data for resorcinol concentration determination have been particularly interesting since no other biosensor device has been reported in literature. In comparison with other biosensors using laccase from the same native source our biosensor has been characterized by larger linear ranges, significant sensitivities and good LODs. To challenge our biosensor with real samples, tap water samples spiked with known amount of catechol and resorcinol have been employed. This article is protected by copyright. All rights reserved