We show that a von Neumann measurement on part of composite quantum system unavoidably creates distillable entanglement between the apparatus and if state has nonzero discord. The minimal is equal to one-way information deficit. discord shown be partial which lost, when we ignore subsystem not measured. then any measure corresponds some correlations. This powerful correspondence also yields necessary properties for generalize results multipartite measurements total system.

We characterize the behavior of quantum correlations under influence local noisy channels. Intuition suggests that such noise should be detrimental for quantumness. When considering qubit systems, we show which channels this is indeed case: The amount can only decrease action unital However, nonunital (e.g., as dissipation) create some initially classical states. Furthermore, higher-dimensional systems even may increase correlations. Thus, counterintuitively, decoherence generate

Establishing quantum entanglement between two distant parties is an essential step of many protocols in information processing. One possibility for providing long-distance to create entangled composite state within a lab and then physically send one subsystem lab. However, this the "cheapest" way? Here, we investigate minimal "cost" that necessary establishing certain amount parties. We prove cost intrinsically quantum, specified by correlations. Our results provide optimal protocol...

The laws of quantum mechanics allow for the distribution a secret random key between two parties. Here we analyse security protocol establishing common N parties (i.e. conference key), using resource states with genuine N-partite entanglement. We compare this to via bipartite entanglement, regarding required resources, achievable rates and threshold qubit error rates. Furthermore discuss networks bottlenecks which our multipartite entanglement-based can benefit from network coding, while...

The resource theory of quantum coherence studies the off-diagonal elements a density matrix in distinguished basis, whereas purity all deviations from maximally mixed state. We establish direct connection between two theories, by identifying as maximal which is achievable unitary operations. states that saturate this maximum identify universal family coherent states. These are optimal resources under incoherent operations, and thus independent way quantified. For distance-based quantifiers...

The establishment of a world-wide quantum communication network relies on the synergistic integration satellite-based links and fiber-based networks. first are helpful for long-distance communication, as photon losses introduced by optical fibers too detrimental lengths greater than about 200 km. This work aims at giving, one hand, comprehensive fundamental model suffered signals during propagation along an atmospheric free-space link. On other performance analysis different Quantum Key...

Quantum coherence is a fundamental feature of quantum mechanics and an underlying requirement for most information tasks. In the resource theory coherence, incoherent states are diagonal with respect to fixed orthonormal basis, i.e., they can be seen as arising from von Neumann measurement. Here, we introduce study generalization defined general measurement, arbitrary positive-operator-valued measure (POVM). We establish POVM-based measures POVM-incoherent operations which coincide case...

Long-distance entanglement is a very precious resource, but its distribution difficult due to the exponential losses of light in optical fibres. A possible solution consists use quantum repeaters, based on swapping or error correction. Alternatively, satellite-based free-space links can be exploited, achieving better loss-distance scaling. We propose combine these two ingredients, repeaters and links, into scheme that allows achieve over global distances with small number intermediate...

We introduce a method to lower bound an entropy-based measure of genuine multipartite entanglement via nonlinear witnesses. show that some these bounds are tight and explicitly work out their connection framework witnesses were published recently. Furthermore, we provide detailed analysis in the context other possible measures. In exemplary cases, only few local measurements necessary determine bounds.

We generalize measurement-device-independent quantum key distribution [ H.-K. Lo, M. Curty, and B. Qi, Phys. Rev. Lett. 108, 130503 (2012) ] to the scenario where Bell-state measurement station contains also heralded memories. find analytical formulas, in terms of device imperfections, for all quantities entering secret rates, i.e., bit error rate repeater rate. assume either single-photon sources or weak coherent pulse plus decoy states. show that it is possible significantly outperform...

We establish a relation between entanglement of many-body system and its diffractive properties, where the link is given by structure factors. Based on these, we provide general analytical construction multiqubit witnesses. The proposed witnesses contain two-point correlations. They could be either measured in scattering experiment or via local measurements, depending underlying physical system. For some explicit examples analyze properties states that are detected them. further study...

An important problem in quantum information theory is the quantification of entanglement multipartite mixed states. In this work, a connection between geometric measure and distance established. We present new expression for terms maximal fidelity with separable state. A direct application result provides closed Bures entanglementof two qubits. also prove that number elements an optimal decomposition w.r.t. bounded from above by Caratheodory bound, we find necessary conditions structure...

Society relies and depends increasingly on information exchange communication. In the quantum world, security privacy is a built-in feature for processing. The essential ingredient exploiting these advantages resource of entanglement, which can be shared between two or more parties. distribution entanglement over large distances constitutes key challenge current research development. Due to losses transmitted particles, typically scale exponentially with distance, intermediate repeater...

We analyze various prominent quantum repeater protocols in the context of long-distance key distribution. These are original proposal by Briegel, D\"ur, Cirac and Zoller, so-called hybrid using optical coherent states dispersively interacting with atomic spin qubits, Duan-Lukin-Cirac-Zoller-type ensembles together linear optics and, its most recent extension, heralded qubit amplifiers. For our analysis, we investigate important experimental parameters every component find their minimally...

We analyze the security of two multipartite quantum key distribution (QKD) protocols, specifically we introduce an $N$-partite version BB84 protocol and discuss six-state proposed in arXiv:1612.05585v2. The analysis proceeds from generalization known results bipartite QKD to scenario, takes into account finite resources. In this context derive a computable expression for achievable rate both protocols by employing best-known strategies: uncertainty relation postselection technique. compare...

Coherence is a cornerstone of quantum theory and prerequisite for the advantage technologies. In recent work, notion coherence with respect to general measurement, i.e., positive operator-valued measure (POVM), was introduced embedded into resource-theoretic framework that generalizes standard resource coherence. particular, POVM-incoherent (free) states operations were established. this we explore features which arise due rich structure POVMs compared projective measurements. Moreover,...

We investigate super dense coding in the presence of noise, i.e. subsystems entangled resource state have to pass a noisy unital quantum channel between sender and receiver. discuss explicitly case Pauli channels an arbitrary dimension derive capacity (i.e. optimal information transfer) for some given states. For qubit depolarizing channel, we also optimize with respect input state. show that, below threshold value noise parameter, protocol is optimized by maximally initial state, while...

We investigate quantum repeaters in the context of key distribution. optimize secret rate per memory second with respect to different distillation protocols and strategies. For this purpose, we also derive an analytical expression for average number entangled pairs created by repeater, including classical communication times entanglement swapping distillation. impact time on rate. Finally, study effect detector efficiency

Users of quantum networks can securely communicate via so-called (quantum) conference key agreement --making their identities publicly known. In certain circumstances, however, communicating users demand anonymity. Here, we introduce a security framework for anonymous with different levels anonymity, which is inspired by the epsilon-security distribution. We present efficient and noise-tolerant protocols exploiting multipartite Greenberger-Horne-Zeilinger (GHZ) states prove in finite-key...

We investigate the advantages of high-dimensional encoding for a quantum key distribution protocol. In particular, we address BBM92-like protocol where dimension systems can be larger than two and more mutually unbiased bases (MUBs) employed. Indeed, it is known that, system whose $d$ prime or power prime, up to $d+1$ MUBs found. derive an analytic expression asymptotic rate when are exploited show effects using different numbers on performance Then, move non-asymptotic case optimize finite...

Quantum key distribution (QKD) is a promising technology for secure communication. Nevertheless, QKD still treated with caution in certain contexts due to potential gaps between theoretical models and actual implementations. A common assumption security proofs that the detection probability at receiver, given input state, independent of measurement basis, which might not always be verified could lead loopholes. This paper presents proof protocols does rely on aforementioned thus applicable...

We revisit the problem of discriminating orthogonal quantum states within local-quantum-operation-and-classical-communication (LOCC) paradigm. Our particular focus is on asymptotic situation where parties have infinite resources and protocol may become arbitrarily long. main result a necessary condition for perfect LOCC discrimination. As an application, we prove that complete product bases, unlimited are no advantage. On other hand, identify example which it still remains undecided whether superior.

Many protocols of quantum information processing, like key distribution or measurement-based computation, 'consume' entangled states during their execution. When participants are located at distant sites, these resource need to be distributed. Due transmission losses repeater become necessary for large distances (e.g. ). Here we generalize the concept graph state D-dimensional and repeaters that can perform basic computations, which call routers. This processing data intermediate network...

The authors introduce a new family of multipartite Bell inequalities and analytically characterize their features. paper demonstrates the usefulness relations for device-independent quantum key distribution, which requires with specific structure.