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We develop a device-independent framework for testing quantum channels. That is, we falsify a hypothesis about a quantum channel based only on an observed set of input-output correlations. Formally, the problem consists of characterizing the set of input-output correlations compatible with any arbitrary given quantum channel. For binary (i.e., two input symbols, two output symbols) correlations, we show that extremal correlations are always achieved by orthogonal encodings and measurements, irrespective of whether or not the channel preserves commutativity. We further provide a full, closed-form characterization of the sets of binary correlations in the case of: i) any dihedrally-covariant qubit channel (such as any Pauli and amplitude-damping channels), and ii) any universally-covariant commutativity-preserving channel in an arbitrary dimension (such as any erasure, depolarizing, universal cloning, and universal transposition channels)., 10 pages, 2 figures, 2 tables, extends arXiv:1511.05260

The crucial feature of a memoryless stochastic process is that any information about its state can only decrease as the system evolves. Here we show that such a decrease of information is equivalent to the underlying stochastic evolution being divisible. The main result, which holds for both classical and quantum stochastic processes, rely on a quantum version of the so-called Blackwell-Sherman-Stein theorem in classical statistics., v3: published version. v2: extensive revision, lot of references added, same results. v1: 5+2 pages, 1 figure

This chapter focuses on how celebrity chefs support meat consumption. Every day in Europe and in the USA, on myriads of food shows, celebrity chefs, TV presenters, journalists, and amateurs cook, recommend, and eat meat. On the face of it, this seems benign in a “carnist” culture,1 as people are free to decide what to cook and eat in front of the camera. However, what television hides in these frequent representations is that for the last 20 years the scientific community has been considering meat as a problem for both the external environment and the human body. I will return to this division between the external environment and the body at the end of this chapter. What is important to note here is that disease, pathogens, medical costs, pollution, and animal suffering are among the issues linked to meat consumption. These issues are hard to question, as many studies adopting different methodologies, perspectives, and theories point to the fact that meat eating contributes significantly to all of them. Among the many examples, Joseph DesJardins, Sjur Kasa, and Philip Lymbery and Isabel Oakeshott2 offer a good overview and provide useful literature on all of this. The present chapter focuses on why these studies, and many others demonstrating the dangerousness of meat-eating, have not changed the media perception of meat.

We explicitly construct a large class of unitary transformations that allow to perform the ideal estimation of the phase-shift on a single-mode radiation field. The ideal phase distribution is obtained by heterodyne detection on two radiation modes after the interaction., 7 pages, no figures. Elsart style

Information-theoretic definitions for noise and disturbance in quantum measurements were given in Phys. Rev. Lett. 112, 050401 (2014) and a state-independent noise-disturbance uncertainty relation was obtained. Here, we derive a tight noise-disturbance uncertainty relation for complementary qubit observables and carry out an experimental test. Successive projective measurements on the neutron's spin-1/2system, together with a correction procedure which reduces the disturbance, are performed. Our experimental results saturate the tight noise-disturbance uncertainty relation for qubits when an optimal correction procedure is applied., Comment: 5 pages, 5 figures plus Supplemental Material (5 pages, 4 figures)

We provide, in an extremely simple way, an upper bound to the minimum number of unitary operators describing a general random-unitary channel., Comment: Final version accepted for publication. One wrong equation has been corrected, two notes and one reference have been added

This article analyses the gender issues raised by the representation of the woman in the kitchen on Italian food TV. In Italy, food and women have always been constructed as a whole, but today this model seems to be redundant. Controversial postfeminist readings of Nigella’s cooking shows and Williams’ categories of dominant, emergent and residual help investigate, in a constructivist sense, how Italian TV deals with this social change. Through qualitative, semiotic and gender analyses, the article focuses on three Italian food shows broadcast at noon. Results show that the three programmes mediate the role of the woman, drawing on the model of trattorie, traditional Italian restaurants in which the women cook and the men serve the tables. This negotiation helps balance gender relations without revolutionary outcomes. In fact, at the same time, it modernises the old model of the housewife and does not move the woman out of the kitchen.

Purpose – The purpose of this paper is to investigate how in Britain, France and Italy the idea of the living animal is being detached from the action of eating meat. It is an ongoing historical process, which has recently been fuelled by the new issue of cultured meat. Design/methodology/approach – Starting from Goody's developmentalist stages (Production, Distribution, Preparation and Consumption), first this work analyses historically how these stages have undergone the process of the disappearance of the animal origins of meat (animal origins of meat are parts like the head and legs that remind us that once meat was an animal). Second, this paper applies cultured meat to Goody's stage of Production, linking the new product to the historical, above described, process. Findings – The analysis shows that, in the past, Goody's stages of Consumption, Distribution and Preparation witnessed the disappearance of the animal origins of meat, while Production was not affected by the phenomenon. Today, with testing on cultured meat, even the stage of Production has gone through this process. Now, all of Goody's stages are involved in the process. Usually considered a shocking novelty, cultured meat is instead a stage of a historical process. Originality/value – No one has previously analysed the disappearance of the animal origins of meat relating it to Goody's stages, and a current issue like cultured meat has never been considered a further step of this process.

Recently, a novel operational strategy to access quantum correlation functions of the form Tr[A rho B] was provided in [F. Buscemi, M. Dall'Arno, M. Ozawa, and V. Vedral, arXiv:1312.4240]. Here we propose a realization scheme, that we call partial expectation values, implementing such strategy in terms of a unitary interaction with an ancillary system followed by the measurement of an observable on the ancilla. Our scheme is universal, being independent of rho, A, and B, and it is optimal in a statistical sense. Our scheme is suitable for implementation with present quantum optical technology, and provides a new way to test uncertainty relations., Comment: 5 pages, 2 figures, submitted as a proceeding of the Quantum 2014 conference, Turin, Italy, 25-31 May, 2014

We show that complete positivity is not only sufficient but also necessary for the validity of the quantum data-processing inequality. As a consequence, the reduced dynamics of a quantum system are completely positive, even in the presence of initial correlations with its surrounding environment, if and only if such correlations do not allow any anomalous backward flow of information from the environment to the system. Our approach provides an intuitive information-theoretic framework to unify and extend a number of previous results., v3: to appear in Physical Review Letters, 5+3 pages, 2 color figures; v2: 10 pages, much improved, 2 figures; v1: 7 pages, preliminary version posted to encourage comments

Varia; International audience; The arrival of Napoleonic troops in Italy shape the way Italians imagine political change. This article shows how this odd revolution, imported by French armies, was described by Italian patriots: an intimate, deep regeneration of Italian society and individuals. In the new republican system, citizens are supposed to live politics as a religious or sentimental experience.In the Nineteenth Century, even if Risorgimento owes a lot to ideas and men from the French Revolution, Italians patrioti do not live in the nostalgia of revolutionary times. Otherwise, they challenge the French revolutionary model, trying to make their efforts towards Italian unification stand out. This battle against the French Revolution is led by both moderates and democrats of the Italian nationalistic movement, even if their purposes are very different.; L’arrivée de troupes napoléoniennes en Italie en 1796 façonne la manière dont les italiens conçoivent le changement en politique. Tout d’abord, l’article veut démontrer comment la drôle de révolution apportée par les armées françaises soit décrite comme une régénération intime et profonde de la société italienne. Dans les nouveaux régimes républicains les citoyens sont censés vivre la vie politique comme une expérience religieuse ou sentimentale.Dans le XIXe siècle, alors que le contact avec les idées et les hommes de la Révolution française est un des ingrédients principaux des origines culturelles du Risorgimento, les patriotes italiens ne se lézardent pas sur le souvenir de la décennie révolutionnaire. Ils lancent plutôt un défi intellectuel et politique au modèle révolutionnaire français, en cherchant de distinguer leur activisme pour l’unification italienne de la mémoire de 1789. À cette entreprise les modérés et les démocrates qui composent le mouvement nationaliste italien participent avec le même zèle, même si leurs finalités restent très différentes.

We introduce information-theoretic definitions for noise and disturbance in quantum measurements and prove a state-independent noise-disturbance tradeoff relation that these quantities have to satisfy in any conceivable setup. Contrary to previous approaches, the information-theoretic quantities we define are invariant under relabelling of outcomes, and allow for the possibility of using quantum or classical operations to `correct' for the disturbance. We also show how our bound implies strong tradeoff relations for mean square deviations., Comment: v3: to appear on PRL (some issues fixed, supplemental material expanded). v2: replaced with submitted version; 5 two-column pages + 6 one-column pages + 3 figures; one issue corrected and few references added. v1: 17 pages, 3 figures

Winter's measurement compression theorem stands as one of the most penetrating insights of quantum information theory (QIT). In addition to making an original and profound statement about measurement in quantum theory, it also underlies several other general protocols in QIT. In this paper, we provide a full review of Winter's measurement compression theorem, detailing the information processing task, giving examples for understanding it, reviewing Winter's achievability proof, and detailing a new approach to its single-letter converse theorem. We prove an extension of the theorem to the case in which the sender is not required to receive the outcomes of the simulated measurement. The total cost of common randomness and classical communication can be lower for such a "non-feedback" simulation, and we prove a single-letter converse theorem demonstrating optimality. We then review the Devetak-Winter theorem on classical data compression with quantum side information, providing new proofs of its achievability and converse parts. From there, we outline a new protocol that we call "measurement compression with quantum side information," announced previously by two of us in our work on triple trade-offs in quantum Shannon theory. This protocol has several applications, including its part in the "classically-assisted state redistribution" protocol, which is the most general protocol on the static side of the quantum information theory tree, and its role in reducing the classical communication cost in a task known as local purity distillation. We also outline a connection between measurement compression with quantum side information and recent work on entropic uncertainty relations in the presence of quantum memory. Finally, we prove a single-letter theorem characterizing measurement compression with quantum side information when the sender is not required to obtain the measurement outcome., 77 pages, 7 figures; v2, minor changes to clarify notation

Departing from the usual paradigm of local operations and classical communication adopted in entanglement theory, here we study the interconversion of quantum states by means of local operations and shared randomness. A set of necessary and sufficient conditions for the existence of such a transformation between two given quantum states is given in terms of the payoff they yield in a suitable class of nonlocal games. It is shown that, as a consequence of our result, such a class of nonlocal games is able to witness quantum entanglement, however weak, and reveal nonlocality in any entangled quantum state. An example illustrating this fact is provided., 4+2 pages. Final version published in PRL. The related APS Physics Viewpoint can be found at http://dx.doi.org/10.1103/Physics.5.56

A family of probability distributions (i.e. a statistical model) is said to be sufficient for another, if there exists a transition matrix transforming the probability distributions in the former to the probability distributions in the latter. The Blackwell-Sherman-Stein (BSS) theorem provides necessary and sufficient conditions for one statistical model to be sufficient for another, by comparing their information values in statistical decision problems. In this paper we extend the BSS theorem to quantum statistical decision theory, where statistical models are replaced by families of density matrices defined on finite-dimensional Hilbert spaces, and transition matrices are replaced by completely positive, trace-preserving maps (i.e. coarse-grainings). The framework we propose is suitable for unifying results that previously were independent, like the BSS theorem for classical statistical models and its analogue for pairs of bipartite quantum states, recently proved by Shmaya. An important role in this paper is played by statistical morphisms, namely, affine maps whose definition generalizes that of coarse-grainings given by Petz and induces a corresponding criterion for statistical sufficiency that is weaker, and hence easier to be characterized, than Petz's., v4: final version to appear on Communications in Mathematical Physics. v3: submitted version, further improvements and results added, still 23 pages. v2: presentation improved and new results added, now 23 pages. v1: 20 pages, article class, no figures

We obtain the general formula for the optimal rate at which singlets can be distilled from any given noisy and arbitrarily correlated entanglement resource, by means of local operations and classical communication (LOCC). Our formula, obtained by employing the quantum information spectrum method, reduces to that derived by Devetak and Winter, in the special case of an i.i.d. resource. The proofs rely on a one-shot version of the so-called "hashing bound," which in turn provides bounds on the one-shot distillable entanglement under general LOCC., 24 pages, article class, no figure. v2: references added, published version

While quantum entanglement is known to be monogamous (i.e. shared entanglement is restricted in multi-partite settings), here we show that distributed entanglement (or the potential for entanglement) is by nature polygamous. By establishing the concept of one-way unlocalizable entanglement (UE) and investigating its properties, we provide a polygamy inequality of distributed entanglement in tripartite quantum systems of arbitrary dimension. We also provide a polygamy inequality in multi-qubit systems, and several trade offs between UE and other correlation measures., 9 pages, 1 figure, few typos corrected

We quantify the one-shot entanglement cost of an arbitrary bipartite state, that is the minimum number of singlets needed by two distant parties to create a single copy of the state up to a finite accuracy, using local operations and classical communication only. This analysis, in contrast to the traditional one, pertains to scenarios of practical relevance, in which resources are finite and transformations can only be achieved approximately. Moreover, it unveils a fundamental relation between two well-known entanglement measures, namely, the Schmidt number and the entanglement of formation. Using this relation, we are able to recover the usual expression of the entanglement cost as a special case., Comment: 4+4 pages. See also arXiv:0704.1957; v2: minor typos corrected; v3: final version to appear on PRL

We propose an experimental implementation of a particular attack against the BB84 quantum key distribution protocol, utilizing a 1→3 asymmetric phase‐covariant quantum cloning. Our eavesdropping strategy is numerically optimized to extract the information about the input state. The proposed cloning circuit is easily implementable with linear optics and its performances turn out to be well close to the optimum attack.

It is shown that, if the loss of entanglement along a quantum channel is sufficiently small, then approximate quantum error correction is possible, thereby generalizing what happens for coherent information. Explicit bounds are obtained for the entanglement of formation and the distillable entanglement, and their validity naturally extends to other bipartite entanglement measures in between. Robustness of derived criteria is analyzed and their tightness compared. Finally, as a byproduct, we prove a bound quantifying how large the gap between entanglement of formation and distillable entanglement can be for any given finite dimensional bipartite system, thus providing a sufficient condition for distillability in terms of entanglement of formation., 7 pages, two-columned revtex4, no figures. v1: Deeply revised and extended version: different entanglement measures are separately considered, references are added, and some remarks are stressed. v2: Added a sufficient condition for distillability in terms of entanglement of formation; published version

We show that the global balance of information dynamics for general quantum measurements given in [F. Buscemi, M. Hayashi, and M. Horodecki, Phys. Rev. Lett. 100, 210504 (2008)] makes it possible to unify various and generally inequivalent approaches adopted in order to derive information-disturbance tradeoffs in quantum theory. We focus in particular on those tradeoffs, constituting the vast majority of the literature on the subject, where disturbance is defined either in terms of average output fidelity or of entanglement fidelity.

By exploiting a generalization of recent results on environment-assisted channel correction, we show that, whenever a quantum system undergoes a channel realized as an interaction with a probe, the more efficiently the information about the input state can be erased from the probe, the higher is the corresponding entanglement fidelity of the corrected channel, and vice-versa. The present analysis applies also to channels for which perfect quantum erasure is impossible, thus extending the original quantum eraser arrangement, and naturally embodies a general information-disturbance tradeoff., 4 pages RevTex4. Revised version, drastically modified. To appear on PRL

We perform an information-theoretical analysis of quantum measurement processes and obtain the global information balance in quantum measurements, in the form of a closed chain equation for quantum mutual entropies. Our balance provides a tight and general entropic information-disturbance trade-off, and explains the physical mechanism underlying it. Finally, the single-outcome case, that is, the case of measurements with post-selection, is briefly discussed., Final version to appear on Physical Review Letters

We consider the classical algebra of observables that are diagonal in a given orthonormal basis, and define a complete decoherence process as a completely positive map that asymptotically converts any quantum observable into a diagonal one, while preserving the elements of the classical algebra. For quantum systems in dimension two and three any decoherence process can be undone by collecting classical information from the environment and using such an information to restore the initial system state. As a relevant example, we illustrate the quantum eraser of Scully et al. [Nature 351, 111 (1991)] as an example of environment-assisted correction. Moreover, we present the generalization of the eraser setup for d-dimensional systems, showing that any von Neumann measurement on a system can be undone by a complementary measurement on the environment., 10 pages, 1 figure

We address the problem of broadcasting N copies of a generic qubit state to M>N copies by estimating its direction and preparing a suitable output state according to the outcome of the estimate. This semiclassical broadcasting protocol is more restrictive than a general one, since it requires an intermediate step where classical information is extracted and processed. However, we prove that a suboptimal superbroadcasting, namely broadcasting with simultaneous purification of the local output states with respect to the input ones, is possible. We show that in the asymptotic limit of $M \to \infty$ the purification rate converges to the optimal one, proving the conjecture that optimal broadcasting and state estimation are asymptotically equivalent. We also show that it is possible to achieve superbroadcasting with simultaneous inversion of the Bloch vector direction (universal NOT). We prove that in this case the semiclassical procedure of state estimation and preparation turns out to be optimal. We finally analyse semiclassical superbroadcasting in the phase-covariant case., 9 pages, 2 figures

We describe a general framework to study covariant symmetric broadcasting maps for mixed qubit states. We explicitly derive the optimal N to M superbroadcasting maps, achieving optimal purification of the single-site output copy, in both the universal and the phase covariant cases. We also study the bipartite entanglement properties of the superbroadcast states., Comment: 19 pages, 8 figures, strictly related to quant-ph/0506251 and quant-ph/0510155

When discriminating between two pure quantum states, there exists a quantitative tradeoff between the information retrieved by the measurement and the disturbance caused on the unknown state. We derive the optimal tradeoff and provide the corresponding quantum measurement. Such an optimal measurement smoothly interpolates between the two limiting cases of maximal information extraction and no measurement at all., Comment: 5 pages, 2 (low-quality) figures. Eq. (20) corrected. Final published version

Even though the time-reversal is unphysical (it corresponds to the complex conjugation of the density matrix), for some restricted set of states it can be achieved unitarily, typically when there is a common de-phasing in a n-level system. However, in the presence of multiple phases (i. e. a different de-phasing for each element of an orthogonal basis occurs) the time reversal is no longer physically possible. In this paper we derive the channel which optimally approaches in fidelity the time-reversal of multi-phase equatorial states in arbitrary (finite) dimension. We show that, in contrast to the customary case of the Universal-NOT on qubits (or the universal conjugation in arbitrary dimension), the optimal phase covariant time-reversal for equatorial states is a nonclassical channel, which cannot be achieved via a measurement/preparation procedure. Unitary realizations of the optimal time-reversal channel are given with minimal ancillary dimension, exploiting the simplex structure of the optimal maps., Comment: 7 pages, minor changes

In quantum mechanics the statistics of the outcomes of a measuring apparatus is described by a positive operator valued measure (POVM). A quantum channel transforms POVM's into POVM's, generally irreversibly, thus loosing some of the information retrieved from the measurement. This poses the problem of which POVM's are "undisturbed", namely they are not irreversibly connected to another POVM. We will call such POVM clean. In a sense, the clean POVM's would be "perfect", since they would not have any additional "extrinsical" noise. Quite unexpectedly, it turns out that such cleanness property is largely unrelated to the convex structure of POVM's, and there are clean POVM's that are not extremal and vice-versa. In this paper we solve the cleannes classification problem for number n of outcomes nd, along with an iff condition for the case of informationally complete POVM's for n=d^2., Minor changes. amsart 21 pages. Accepted for publication on J. Math. Phys

We show that for qubits and qutrits it is always possible to perfectly recover quantum coherence by performing a measurement only on the environment, whereas for dimension d>3 there are situations where recovery is impossible, even with complete access to the environment. For qubits, the minimal amount of classical information to be extracted from the environment equals the entropy exchange., Phys. Rev. Lett. 95, 090501 (2005). Published version

We derive the optimal N to M phase-covariant quantum cloning for equatorial states in dimension d with M=kd+N, k integer. The cloning maps are optimal for both global and single-qudit fidelity. The map is achieved by an ``economical'' cloning machine, which works without ancilla., Comment: 10 pages revtex4, 7 figures, replaced with modified version

Quantum operations (QO) describe any state change allowed in quantum mechanics, such as the evolution of an open system or the state change due to a measurement. We address the problem of which unitary transformations and which observables can be used to achieve a QO with generally different input and output Hilbert spaces. We classify all unitary extensions of a QO, and give explicit realizations in terms of free-evolution direct-sum dilations and interacting tensor-product dilations. In terms of Hilbert space dimensionality the free-evolution dilations minimize the physical resources needed to realize the QO, and for this case we provide bounds for the dimension of the ancilla space versus the rank of the QO. The interacting dilations, on the other hand, correspond to the customary ancilla-system interaction realization, and for these we derive a majorization relation which selects the allowed unitary interactions between system and ancilla., Comment: 8 pages, no figures. Accepted for publication on Phys. Rev. A

We show that, contrarily to the widespread belief, in quantum mechanics repeatable measurements are not necessarily described by orthogonal projectors--the customary paradigm of "observable". Nonorthogonal repeatability, however, occurs only for infinite dimensions. We also show that when a non orthogonal repeatable measurement is performed, the measured system retains some "memory" of the number of times that the measurement has been performed., 4 pages, 1 figure, revtex4, minor changes

We solve the problem of achieving the optimal physical approximation of the transposition for pure states of arbitrary quantum systems for finite and infinite dimensions. A unitary realization is also given for any finite dimension, which provides the optimal quantum cloning map of the ancilla as well., Comment: 10 pages. No figures. Elsart style

We introduce a guessing game involving a quantum channel, three parties - the sender, the receiver and an eavesdropper, Eve - and a quantum public side channel. We prove that a necessary and sufficient condition for the quantum channel to be antidegradable, is that Eve wins the game. We thus obtain a complete operational characterization of antidegradable channels in a game-theoretic framework., Comment: v2: published version, 14 pages, 1 figure; v1: 13 pages, 1 figure

Institute for Advanced Research, Nagoya University, Chikusa-ku, Nagoya 464-8601, Japan(Dated: February 5, 2014)The accessible information quantifies the amount of classical information that can be extractedfrom an ensemble of quantum states. Analogously, the informational power quantifies the amountof classical information that can be extracted by a quantum measurement. For both quantities,we provide upper and lower bounds that depend only on the dimension of the system, and weprove their tightness. In the case of symmetric informationally complete (SIC) ensembles andmeasurements, stronger bounds are provided and their tightness proved for qubits and qutrits. Fromour upper bounds, we notice, perhaps surprisingly, that the statistics generated by SIC ensemblesor measurements in arbitrary dimension, though optimal for tomographic purposes, in fact nevercontains more than just one bit of information, the rest being constituted by completely randombits. On the other hand, from our lower bounds, we obtain an explicit strategy beating the so-called “pretty-good” one for the extraction of mutual information in the case of SIC ensembles andmeasurements.I. INTRODUCTION

Given a bipartite system, correlations between its subsystems can be understood as information that each one carries about the other. In order to give a model-independent description of secure information disposal, we propose the paradigm of private quantum decoupling, corresponding to locally reducing correlations in a given bipartite quantum state without transferring them to the environment. In this framework, the concept of private local randomness naturally arises as a resource, and total correlations get divided into eliminable and ineliminable ones. We prove upper and lower bounds on the amount of ineliminable correlations present in an arbitrary bipartite state, and show that, in tripartite pure states, ineliminable correlations satisfy a monogamy constraint, making apparent their quantum nature. A relation with entanglement theory is provided by showing that ineliminable correlations constitute an entanglement parameter. In the limit of infinitely many copies of the initial state provided, we compute the regularized ineliminable correlations to be measured by the coherent information, which is thus equipped with a new operational interpretation. In particular, our results imply that two subsystems can be privately decoupled if their joint state is separable., Comment: Child of 0807.3594 v2: minor changes v3: presentation improved, one figure added v4: extended version with a lot of discussions and examples v5: published version

We describe a unified framework of phase covariant multi user quantum transformations for d-dimensional quantum systems. We derive the optimal phase covariant cloning and transposition tranformations for multi phase states. We show that for some particular relations between the input and output number of copies they correspond to economical tranformations, which can be achieved without the need of auxiliary systems. We prove a relation between the optimal phase covariant cloning and transposition maps, and optimal estimation of multiple phases for equatorial states., 18 pages, 1 fugure. This paper reviews and completes quant-ph/0407103 and quant-ph/0504016