Quantum resources for purification and cooling: fundamental limits and opportunities

Preparing a quantum system in a pure state is ultimately limited by the nature of the system's evolution in the presence of its environment and by the initial state of the environment itself. We show that, when the system and environment are initially uncorrelated and arbitrary joint unitary dynamics is allowed, the system may be purified up to a certain (possibly arbitrarily small) threshold if and only if its environment, either natural or engineered, contains a "virtual subsystem" which has the same dimension and is in a state with the desired purity. Beside providing a unified understanding of quantum purification dynamics in terms of a "generalized swap process," our results shed light on the significance of a no-go theorem for exact ground-state cooling, as well as on the quantum resources needed for achieving an intended purification task.Comment: 10 pages, 2 figure

Quantum and classical resources for unitary design of open-system evolutions

A variety of tasks in quantum control, ranging from purification and cooling to quantum stabilisation and open-system simulation, rely on the ability to implement a target quantum channel over a specified time interval within prescribed accuracy. This can be achieved by engineering a suitable unitary dynamics of the system of interest along with its environment, which, depending on the available level of control, is fully or partly exploited as a coherent quantum controller. After formalising a controllability framework for completely positive trace-preserving quantum dynamics, we provide sufficient conditions on the environment state and dimension that allow for the realisation of relevant classes of quantum channels, including extreme channels, stochastic unitaries or simply any channel. The results hinge on generalisations of Stinespring's dilation via a subsystem principle. In the process, we show that a conjecture by Lloyd on the minimal dimension of the environment required for arbitrary open-system simulation, albeit formally disproved, can in fact be salvaged, provided that classical randomisation is included among the available resources. Existing measurement-based feedback protocols for universal simulation, dynamical decoupling and dissipative state preparation are recast within the proposed coherent framework as concrete applications, and the resources they employ discussed in the light of the general results

Quantum Markovian Subsystems: Invariance, Attractivity, and Control

We characterize the dynamical behavior of continuous-time, Markovian quantum systems with respect to a subsystem of interest. Markovian dynamics describes a wide class of open quantum systems of relevance to quantum information processing, subsystem encodings offering a general pathway to faithfully represent quantum information. We provide explicit linear-algebraic characterizations of the notion of invariant and noiseless subsystem for Markovian master equations, under different robustness assumptions for model-parameter and initial-state variations. The stronger concept of an attractive quantum subsystem is introduced, and sufficient existence conditions are identified based on Lyapunov's stability techniques. As a main control application, we address the potential of output-feedback Markovian control strategies for quantum pure state-stabilization and noiseless-subspace generation. In particular, explicit results for the synthesis of stabilizing semigroups and noiseless subspaces in finite-dimensional Markovian systems are obtained.Comment: 16 pages, no figures. Revised version with new title, corrected typos, partial rewriting of Section III.E and some other minor change

Quantum State Preparation by Controlled Dissipation in Finite Time: From Classical to Quantum Controllers

We propose a general scheme for dissipatively preparing arbitrary pure quantum states on a multipartite qubit register in a finite number of basic control blocks. Our "splitting-subspace" approach relies on control resources that are available in a number of scalable quantum technologies (complete unitary control on the target system, an ancillary resettable qubit and controlled-not gates between the target and the ancilla), and can be seen as a "quantum-controller" implementation of a sequence of classical feedback loops. We show how a large degree of flexibility exists in engineering the required conditional operations, and make explicit contact with a stabilization protocol used for dissipative quantum state preparation and entanglement generation in recent experiments with trapped ions.Comment: 10 pages, 2 figures. Submitted to CDC 201

¿Los derechos humanos,son derechos naturales?

L'articolo difende la tesi della profonda differenza fra i diritti umani e i diritti natural

Los derechos y las etades de la vida humana

the author proposes a vision for the human right based in the different stages of the natural human life that overcomes the abstract and ahistorical visión of them. In front of the universal justification insufficiency from the theories of the will and interest, the consideration based in the different truly universal and common stages, gives an universal justification of the human rights and specially of the human of the children and elder but not as special human rights but as essential human rights of every human being

Ermeneutica filosofica, pluralismo e diritto

The purpose of this essay is to show that philosophical hermeneutics is particularly suited for facing problems of understanding among different cultural worlds. These issues are relevant even for legal interpretation that, now more than ever, is not up against culturally homogeneous societies and against legal systems shaped by a single source or by a steady hierarchy of sources. Therefore, philosophical hermeneutics’ approaches to intercultural dialogue can be useful to the present practice of legal interpretation, not by building new interpretative methods, but by clarifying contexts which give significance to legal practice. The paths trodden by legal philosophical hermeneutics are devoted to the understanding of texts which have a paradigmatic feature for jurists’ work and to the identification of legal practice’s ends and values. These paths are complementary, not alternative. The historic consciousness and the practice reason are both essential for the discovery of legal meaning, within which legal interpretation articulates

I diritti in carcere

Si esamina il problema del sovraffollamento delle carceri in relazione al principio costituzionale della funzione di rieducazione della pen

La disponibilità della vita umana.Linee generali

L'articolo esplora i problemi principali sollevati dal diritto di rifiutare le cura e dal testamento biologic