Information-flux approach to multiple-spin dynamics

We introduce and formalize the concept of information flux in a many-body register as the influence that the dynamics of a specific element receive from any other element of the register. By quantifying the information flux in a protocol, we can design the most appropriate initial state of the system and, noticeably, the distribution of coupling strengths among the parts of the register itself. The intuitive nature of this tool and its flexibility, which allow for easily manageable numerical approaches when analytic expressions are not straightforward, are greatly useful in interacting many-body systems such as quantum spin chains. We illustrate the use of this concept in quantum cloning and quantum state transfer and we also sketch its extension to non-unitary dynamics.Comment: 7 pages, 4 figures, RevTeX

A deeper insight into quantum state transfer from an information flux viewpoint

We use the recently introduced concept of information flux in a many-body register in order to give an alternative viewpoint on quantum state transfer in linear chains of many spins.Comment: 6 pages, 3 figures, RevTeX

Non-Markovian qubit dynamics in a circuit-QED setup

We consider a circuit-QED setup that allows the induction and control of non-Markovian dynamics of a qubit. Non-Markovianity is enforced over the qubit by means of its direct coupling to a bosonic mode which is controllably coupled to other qubit-mode system. We show that this configuration can be achieved in a circuit-QED setup consisting of two initially independent superconducting circuits, each formed by one charge qubit and one transmission-line resonator, which are put in interaction by coupling the resonators to a current-biased Josephson junction. We solve this problem exactly and then proceed with a thorough investigation of the emergent non-Markovianity in the dynamics of the qubits. Our study might serve the context for a first experimental assessment of non-Markovianity in a multi-element solid-state device.Comment: 8 pages, 7 figures, slightly changed titl

Bypassing state initialization in Hamiltonian tomography on spin-chains

We provide an extensive discussion on a scheme for Hamiltonian tomography of a spin-chain model that does not require state initialization [Phys. Rev. Lett. 102, 187203 (2009)]. The method has spurred the attention of the physics community interested in indirect acquisition of information on the dynamics of quantum many-body systems and represents a genuine instance of a control-limited quantum protocol.Comment: 7 pages, 2 figures, RevTeX

Use of dynamical coupling for improved quantum state transfer

We propose a method to improve quantum state transfer in transmission lines. The idea is to localize the information on the last qubit of a transmission line, by dynamically varying the coupling constants between the first and the last pair of qubits. The fidelity of state transfer is higher then in a chain with fixed coupling constants. The effect is stable against small fluctuations in the system parameters.Comment: 5 pages, 7 figure

Phase-space interference in extensive and non-extensive quantum heat engines

Quantum interference is at the heart of what sets the quantum and classical worlds apart. We demonstrate that quantum interference effects involving a many-body working medium is responsible for genuinely non-classical features in the performance of a quantum heat engine. The features with which quantum interference manifests itself in the work output of the engine depends strongly on the extensive nature of the working medium. While identifying the class of work substances that optimize the performance of the engine, our results shed light on the optimal size of such media of quantum workers to maximize the work output and efficiency of quantum energy machines

Belief in a Secular Age: Charles Taylor, John Henry Newman, and the New Evangelization

We are currently living in what has been dubbed “a secular age.” Religious affiliation has gone down, leading to a phenomenon in the West known as “the rise of the Nones.” At the same time, from the time of the Gospels, the Church understands herself to be charged by Jesus Christ with the obligation to “make disciples of all nations” (Mt. 28:19). Recent popes have likewise affirmed that we are obliged to go out and propose faith in Jesus to the world. Beginning with John Paul II, a “new evangelization” has been proposed, where the Church evangelizes and makes disciples in places where Christian belief once was common, but has now waned. This work seeks first of all to advance the project of the New Evangelization. Evangelization cannot happen in a vacuum, however, and we must be mindful of what people find credible. Just as Jesus did not berate Thomas for his doubt, but rather gave Thomas what he needed for belief, so too the Church cannot merely berate the modern world for unbelief, but give it what it needs for belief. Thus, it is necessary that we first ask what people need to believe in general. In the first chapter, drawing heavily from Charles Taylor’s work A Secular Age, we will get a feel for the conditions of belief in the contemporary world, and then flesh out our notions by drawing upon various sociological and historical studies of current unbelief, especially Cristal Manning’s book Losing our Religion. In the second chapter, we once again begin with Taylor, focusing on the excarnate trend in knowing, where starting in the Enlightenment our senses, feelings, and experiences were obstacles to knowing. We will then contrast this with the approach of 19th century British thinker John Henry Newman, whose work Grammar of Assent sought iv to push back against these excarnating trends, especially in the concept of the Illative Sense that he developed in the book. Finally, we will explore how Newman’s Personalism—his grasp of the dignity of the whole person—can be seen in how he proposes Christianity for belief to others. Newman prioritizes reality over ideas, and so will stress Biblical images, saints, sacraments, liturgy, and history—all as a way of gaining an image of the person of Jesus. From these images and experiences had by the whole person, we may propose Christianity in a credible manner, and the Church may continue to be faithful to her mandate from Jesus to introduce Him to all peoples

Nested entangled states for distributed quantum channels

We find a coupling-strength configuration for a linear chain of N spins which gives rise to simultaneous multiple Bell states. We suggest a way such an interesting entanglement pattern can be used in order to distribute maximally entangled channels to remote locations and generate multipartite entanglement with a minimum-control approach. Our proposal thus provides a way to achieve the core resources in distributed information processing. The schemes we describe can be efficiently tested in chains of coupled cavities interacting with three-level atoms.Comment: 4 pages, 2 figures, RevTeX

Continuous-variable quantum non-demolishing interaction at a distance

A feasible setup of continuous-variable (CV) quantum non-demolishing (QND) interaction at a distance is proposed. If two distant experimentalists are able to locally perform identical QND interactions then the proposed realization requires only a single quantum channel and classical communication between them. A possible implementation of the proposed setup in recent quantum optical laboratories is discussed and an influence of Gaussian noise in the quantum channel on a quality of the implementation is analyzed. An efficient realization of the QND interaction at a distance can be a basic step to possible distributed quantum CV experiments between the distant laboratories.Comment: 5 pages, 2 figure