We present the optimal collective attack on a quantum key distribution protocol in "device-independent" security scenario, where no assumptions are made about way devices work or what system they operate. Our main result is tight bound Holevo information between one of authorized parties and eavesdropper, as function amount violation Bell-type inequality.

Novel methods for information processing are highly desired in our information-driven society. Inspired by the brain's ability to process information, recently introduced paradigm known as 'reservoir computing' shows that complex networks can efficiently perform computation. Here we introduce a novel architecture reduces usually required large number of elements single nonlinear node with delayed feedback. Through an electronic implementation, experimentally and numerically demonstrate...

We develop a novel approach to Bell inequalities based on constraint that the correlations exhibited by local variable theories must satisfy. This is used construct family of for bipartite quantum systems arbitrarily high dimensionality which are strongly resistant noise. In particular, our work gives an analytic description previous numerical results and generalizes them dimensionality.

We present quantum cloning machines that transform $N$ identical qubits into $M>N$ copies and we prove the fidelity (quality) of these is optimal. The connection between measurement discussed in detail. When number clones $M$ tends towards infinity, each clone optimal can be obtained by a on input qubits. More generally, are universal devices to translate information classical information.

Under strong laser illumination, few-layer graphene exhibits both a transmittance increase due to saturable absorption and nonlinear phase shift. Here, we unambiguously distinguish these two optical effects identify real imaginary parts of the complex refractive index graphene. We show that possesses giant n2=10-7cm2W-1, almost nine orders magnitude larger than bulk dielectrics. find decreases with increasing excitation flux but slower absorption. This suggests may be very promising medium,...

It is well known that measurements performed on spatially separated entangled quantum systems can give rise to correlations are nonlocal, in the sense a Bell inequality violated. They cannot, however, be used for superluminal signaling. also it possible write down sets of ``superquantum'' more nonlocal than allowed by mechanics, yet still nonsignaling. Viewed as an information-theoretic resource, superquantum very powerful at reducing amount communication needed distributed computational...

Quantum information processing is the emerging field that defines and realizes computing devices make use of quantum mechanical principles, like superposition principle, entanglement, interference. In this review we study counterpart computing. The abstract form distributed setting called communication complexity. It studies amount information, in terms bits or our case qubits, two spatially separated need to exchange order perform some computational task. Surprisingly, mechanics can be used...

Device-independent quantum key distribution (DIQKD) represents a relaxation of the security assumptions made in usual (QKD). As QKD, DIQKD follows from laws physics, but contrary to it does not rely on any about internal working devices used protocol. In this paper, we present detail proof for protocol introduced Acín et al (2008 Phys. Rev. Lett. 98 230501). This exploits full structure theory (as opposed other proofs that exploit only no-signaling principle), holds against collective...

Reservoir computing is a recently introduced, highly efficient bio-inspired approach for processing time dependent data. The basic scheme of reservoir consists non linear recurrent dynamical system coupled to single input layer and output layer. Within these constraints many implementations are possible. Here we report an optoelectronic implementation based on proposed architecture consisting node delay line. Our sufficiently fast real information processing. We illustrate its performance...

Many dynamical systems, both natural and artificial, are stimulated by time dependent external signals, somehow processing the information contained therein. We demonstrate how to quantify different modes in which can be processed such systems combine them define computational capacity of a system. This is bounded number linearly independent state variables system, equaling it if system obeys fading memory condition. It interpreted as total functions its stimuli compute. Our theory combines...

According to quantum theory, the outcomes obtained by measuring an entangled state necessarily exhibit some randomness if they violate a Bell inequality. In particular, maximal violation of CHSH inequality guarantees that 1.23 bits are generated measurements. However, performing measurements with binary on two subsystems one could in principle generate up randomness. We show correlations arbitrarily little or states entanglement can be used certify close maximum produced. Our results...

Reservoir Computing is a novel computing paradigm which uses nonlinear recurrent dynamical system to carry out information processing. Recent electronic and optoelectronic Computers based on an architecture with single node delay loop have shown performance standardized tasks comparable state-of-the-art digital implementations. Here we report all-optical implementation of Computer, made off-the-shelf components for optical telecommunications. It the saturation semiconductor amplifier as...

Abstract Introduced a decade ago, reservoir computing is an efficient approach for signal processing. State of the art capabilities have already been demonstrated with both computer simulations and physical implementations. If photonic appears to be promising solution ultrafast nontrivial computing, all implementations presented up now require digital pre or post processing, which prevents them from exploiting their full potential, in particular terms processing speed. We address here...

We consider the problem of estimating state a large but finite number N identical quantum systems. As becomes simplifies dramatically. The only relevant measure quality estimation mean quadratic error matrix. Here we present bound on this quantity: Cram\'er-Rao inequality. This succinctly expresses how in case one can trade information about parameter for another. holds arbitrary measurements pure states, separable mixed states---a striking example nonlocality without entanglement not...

In a recent work, Unruh showed that Hawking radiation is unaffected by truncation of free field theory at the Planck scale. His analysis was performed numerically and based on hydrodynamical model. this analytical methods, mathematical physical origin Unruh's result revealed. An alternative scheme which may be more appropriate for black hole physics proposed analyzed. both schemes thermal remains even though transplanckian energies no longer appear. The universality explained working in...

Silicon waveguides are promising $\chi^3$-based photon pair sources. Demonstrations so far have been based on picosecond pulsed lasers. Here, we present the first investigation of generation in silicon a continuous regime. The source is characterized by coincidence measurements. We uncover presence unexpected noise which had not noticed earlier experiments. Subsequently, advances towards integration with other components chip. This demonstrated Sagnac loop interferometer and inside...

The genetic code is known to be efficient in limiting the effect of mistranslation errors. A misread codon often codes for same amino acid or one with similar biochemical properties, so structure and function coded protein remain relatively unaltered. Previous studies have attempted address this question quantitatively, by estimating fraction randomly generated that do better than respect overall robustness. We extended these results investigating role amino-acid frequencies optimality code....

We solve a 20-year old problem posed by Yannakakis and prove that there exists no polynomial-size linear program (LP) whose associated polytope projects to the traveling salesman polytope, even if LP is not required be symmetric. Moreover, we this holds also for cut stable set polytope. These results were discovered through new connection make between one-way quantum communication protocols semidefinite programming reformulations of LPs.

A monochromatic laser pumping a parametric down-conversion crystal generates frequency-entangled photon pairs. We study this experimentally by addressing such photons at telecommunication wavelengths (around $1550$ nm) with fiber-optics components as electro-optic phase modulators and narrow-band frequency filters. The theory underlying our approach uses the notion of frequency-bin entanglement. Our results show that address coherently up to eleven bins, leading an interference pattern which...

Measurements on entangled quantum systems necessarily yield outcomes that are intrinsically unpredictable if they violate a Bell inequality. This property can be used to generate certified randomness in device-independent way, i.e., without making detailed assumptions about the internal working of devices random numbers. Furthermore these numbers also private, appear not only user, but any adversary might possess perfect description devices. Since this process requires small initial seed,...

Reservoir computing is a new bio-inspired computation paradigm. It exploits dynamical system driven by time-dependent input to carry out computation. For efficient information processing, only few parameters of the reservoir needs be tuned, which makes it promising framework for hardware implementation. Recently, electronic, opto-electronic and all-optical experimental computers were reported. In those implementations, nonlinear response provided active devices such as optoelectronic...

We solve a 20-year old problem posed by Yannakakis and prove that no polynomial-size linear program (LP) exists whose associated polytope projects to the traveling salesman polytope, even if LP is not required be symmetric. Moreover, we this holds also for cut stable set polytope. These results were discovered through new connection make between one-way quantum communication protocols semidefinite programming reformulations of LPs.