A Low Complexity Scheme for Entanglement Distributor Buses

For technological purposes and theoretical curiosity, it is very interesting to have a building block that produces a considerable amount of entanglement between on-demand sites through a simple control of a few sites. Here, we consider permanently-coupled spin networks and study entanglement generation between qubit pairs to find low-complexity structures capable of generating considerable entanglement between various qubit pairs. We find that in axially symmetric networks the generated entanglement between some qubit pairs is rather larger than generic networks. We show that in uniformly-coupled spin rings each pair can be considerably entangled through controlling suitable vertices. To set the location of controlling-vertices, we observe that the symmetry has to be broken for a definite time. To achieve this, a magnetic flux can be applied to break symmetry via Aharonov-Bohm effect. Such a set up can serve as an efficient entanglement distributor bus in which each vertex-pair can be efficiently entangled through exciting only one fixed vertex and controlling the evolution time. The low-complexity of this scheme makes it attractive for use in nanoscale quantum information processors.Comment: 23 pages, 4 figures, Major revision, title changed, published versio

Superconducting Nanocircuits for Topologically Protected Qubits

For successful realization of a quantum computer, its building blocks (qubits) should be simultaneously scalable and sufficiently protected from environmental noise. Recently, a novel approach to the protection of superconducting qubits has been proposed. The idea is to prevent errors at the "hardware" level, by building a fault-free (topologically protected) logical qubit from "faulty" physical qubits with properly engineered interactions between them. It has been predicted that the decoupling of a protected logical qubit from local noises would grow exponentially with the number of physical qubits. Here we report on the proof-of-concept experiments with a prototype device which consists of twelve physical qubits made of nanoscale Josephson junctions. We observed that due to properly tuned quantum fluctuations, this qubit is protected against magnetic flux variations well beyond linear order, in agreement with theoretical predictions. These results demonstrate the feasibility of topologically protected superconducting qubits.Comment: 25 pages, 5 figure

FLU IN CHILDREN AFTER A PANDEMIC IN ST. PETERSBURG GENERAL HOSPITAL

Flu monitoring was carried out in children’s general hospital in St. Petersburg within three epidemic seasons (2010–2011, 2011–2012 and 2012–2013). 1916 patients under the age of 18 years were examined with the complex of virologic tests . The natural decreasing of flu incidence and predominant diagnosing in etiologic structure one of the virus serotypes [in the first A(H1N1)pdm09, in the second — A(H3N2)] have been observed during the first two years after a pandemic. In the third season restoration of the main characteristics of epidemic flu situation were detected: polietiology with annual change of serotypes proportions, late start (winter and spring), majority of younger children among hospitalaized patients and a mild course of disease. The most probable candidates [viruses of a subtype A(H3N2)] are revealed as a causal factor of significant increasing of disease incidence with the severe forms in the near future. Laboratory data were confirmed by increase in frequency of the complicated by pneumonia ARI at hospitalized patients during the periods of their maximum registration. All isolates received during the study were corresponded to the referens-strains included in vaccines. Thus, timely and appropriate vaccination during the studied period had to become an effective protection against a flu