Publish in OALib Journal

ISSN: 2333-9721

APC: Only $99


Any time

2019 ( 2 )

2018 ( 8 )

2017 ( 6 )

2016 ( 11 )

Custom range...

Search Results: 1 - 10 of 5677 matches for " Klaus Pedersen "
All listed articles are free for downloading (OA Articles)
Page 1 /5677
Display every page Item
Few qubit atom-light interfaces with collective encoding
Line Hjortshoj Pedersen,Klaus Molmer
Physics , 2008, DOI: 10.1103/PhysRevA.79.012320
Abstract: Samples with few hundred atoms within a few micrometer sized region of space are large enough to provide efficient cooperative absorption and emission of light, and small enough to ensure strong dipole-dipole interactions when atoms are excited into high-lying Rydberg states. Based on a recently proposed collective encoding scheme, we propose to build few-qubit quantum registers in such samples. The registers can store and transmit quantum information in the form of single photons, and they can employ entanglement pumping protocols to perform ideally in networks for scalable quantum computing and long distance quantum communication.
Fidelity of quantum operations
Line Hjortshoj Pedersen,Klaus Molmer,Niels Martin Moller
Physics , 2007, DOI: 10.1016/j.physleta.2007.02.069
Abstract: We present a derivation and numerous applications of a compact explicit formula for the average fidelity of a quantum operation on a finite dimensional quantum system. The formula can be applied to averages over particularly relevant subspaces; it is easily generalized to multi-component systems, and as a special result, we show that when the same completely positive trace-preserving map is applied to a large number of qubits with one-bit fidelity F close to unity, the average fidelity of the operation on the full K-bit register scales as $F^{3K/2}$.
Error correction in ensemble registers for quantum repeaters and quantum computers
Etienne Brion,Line Hjortshoj Pedersen,Mark Saffman,Klaus Molmer
Physics , 2007, DOI: 10.1103/PhysRevLett.100.110506
Abstract: We propose to use a collective excitation blockade mechanism to identify errors that occur due to disturbances of single atoms in ensemble quantum registers where qubits are stored in the collective population of different internal atomic states. A simple error correction procedure and a simple decoherence-free encoding of ensemble qubits in the hyperfine states of alkali atoms are presented.
The distribution of quantum fidelities
Line Hjortshoj Pedersen,Niels Martin Moller,Klaus Molmer
Physics , 2008, DOI: 10.1016/j.physleta.2008.10.034
Abstract: When applied to different input states, an imperfect quantum operation yields output states with varying fidelities, defined as the absolute square of their overlap with the desired states. We present an expression for the distribution of fidelities for a class of operations applied to a general qubit state, and we present general expressions for the variance and input-space averaged fidelities of arbitrary linear maps on finite dimensional Hilbert spaces.
QoS Self-Provisioning and Interference Management for Co-Channel Deployed 3G Femtocells
Troels Kolding,Pawel Ochal,Niels Terp Kjeldgaard J?rgensen,Klaus Pedersen
Future Internet , 2013, DOI: 10.3390/fi5020168
Abstract: A highly efficient self-provisioning interference management scheme is derived for 3G Home Node-Bs (HNB). The proposed scheme comprises self-adjustment of the HNB transmission parameters to meet the targeted QoS (quality of service) requirements in terms of downlink and uplink guaranteed minimum throughput and coverage. This objective is achieved by means of an autonomous HNB solution, where the transmit power of pilot and data are adjusted separately, while also controlling the uplink interference pollution towards the macro-layer. The proposed scheme is evaluated by means of extensive system level simulations and the results show significant performance improvements in terms of user throughput outage probability, power efficiency, femtocell coverage, and impact on macro-layer performance as compared to prior art baseline techniques. The paper is concluded by also showing corresponding measurements from live 3G high-speed packet access (HSPA) HNB field-trials, confirming the validity of major simulation results and assumptions.
Non-adiabatic many-atom quantum state control in few-well systems
Malte C. Tichy,Mads Kock Pedersen,Klaus M?lmer,Jacob F. Sherson
Physics , 2013, DOI: 10.1103/PhysRevA.87.063422
Abstract: We present a fast scheme for arbitrary unitary control of interacting bosonic atoms in a double-well. Assuming fixed inter-well tunnelling rate and intra-well interaction strength, we control the many-atom state by a discrete sequence of shifts of the single-well energies. For strong interactions, resonant tunnelling transitions implement beam-splitter U(2) rotations among atom number eigenstates, which can be combined and, thus, permit full controllability. By numerically optimizing such sequences of couplings at avoided level crossings (CALC), we extend the realm of full controllability to a wide range of realistic interaction parameters, while we remain in the simple control space. We demonstrate the efficiency and the high achievable fidelity of our proposal with non-adiabatic population transfer, N00N-state creation, a C-NOT gate, and a transistor-like, conditional evolution of several atoms.
Density-dependence and within-host competition in a semelparous parasite of leaf-cutting ants
William OH Hughes, Klaus S Petersen, Line V Ugelvig, Dorthe Pedersen, Lene Thomsen, Michael Poulsen, Jacobus J Boomsma
BMC Evolutionary Biology , 2004, DOI: 10.1186/1471-2148-4-45
Abstract: The relationship between parasite density and infection was sigmoidal, with there being an invasion threshold for an infection to occur (an Allee effect). Although spore production was positively density-dependent, parasite fitness decreased with increasing parasite density, indicating within-host scramble competition. The dynamics differed little between the four strains tested. In mixed infections of three strains the infection-growth dynamics were unaffected by parasite heterogeneity.The strength of within-host competition makes dispersal the best strategy for the parasite. Parasite heterogeneity may not have effected virulence or the infection dynamics either because the most virulent strain outcompeted the others, or because the interaction involved scramble competition that was impervious to parasite heterogeneity. The dynamics observed may be common for virulent parasites, such as Metarhizium, that produce aggregated transmission stages. Such parasites make useful models for investigating infection dynamics and the impact of parasite competition.In most models of host-parasite dynamics, the parasites are considered as part of discrete infections, involving only a single parasite. However, as the transmission stages of parasites tend to be clustered, the majority of host-parasite interactions will rather involve multiple parasite individuals. This is particularly the case for those parasites that exhibit a semelparous life-history, releasing all their transmission propagules in a single event that normally coincides with host death [1,2]. In the same models, transmission is assumed to follow the mass action principle, βSI, where S and I are the densities of susceptible and infected individuals respectively and β is a constant describing the probability of infection [3]. Thus the probability of a host becoming infected per unit time will be directly proportional to the number of parasites that it encounters. Host-parasite interactions will also often involve mu
An Enduring Concept for Security Council Reform  [PDF]
Klaus Schlichtmann
Beijing Law Review (BLR) , 2011, DOI: 10.4236/blr.2011.22010
Abstract: UN Security Council reform has been lingering over the years, since it was first seriously considered in the 1990s, after the collapse of the Soviet Union. This paper argues that enlarging the Security Council by adding new permanent and non-permanent members, while many of the Charter provisions vital for the maintenance of international peace and security and disarmament are not in effect, would be counterproductive. Instead, the composition of the Council should be reshuffled and expanded by giving a seat to a prominent member of the Global South, i.e. India, and replacing the seats of France and Britain with a single European representation. While there would be no increase or change in the number of permanent and non-permanent members, the result will be a dramatic increase in the numbers of people represented by the Permanent Five, which then will, in effect, comprise half of the world’s population projected for 2012. The underlying logic is that increasing the number of permanent members (P5) would make the Security Council not only less effective, but also prevent the realization of a fundamental purpose of the United Nations, i.e. the transition from an armed to an unarmed peace. By maintaining the number 5, the effective operation of the consensus principle required for the maintenance of international peace and security during the transition is ensured. It is maintained that the changes proposed in this paper may be regarded as “purely procedural” under Article 27 paragraph 2 of the Charter. It will be seen, however, that to trigger the process of the transition, UN Member states (other than the P5, who bear responsibility under the Charter to guarantee safe passage during the transition) must begin, one by one, to delegate “Security Sovereignty” to the Council.
Prevalence of Common Mental Disorders among Incident Individuals on Long-Term Sickness Absence When Compensating for Non-Participation  [PDF]
Hans Joergen Soegaard, Pernille Pedersen
Psychology (PSYCH) , 2012, DOI: 10.4236/psych.2012.329124
Abstract: Objective: In a cross-sectional study regarding long-term sickness absence to estimate: 1) The prevalence of mental disorders among incident individuals on long-term sickness absence; 2) The diagnostic frequencies in total and divided by participants and non-participants; and 3) Divided by socio-demographic characteristics. Method: In a well-defined cohort with complete coverage, 2414 individuals entering LSA during one year were identified. In a two-phase study, the 1121 (46.4%) participants constituted Phase 1 and they were screened for mental disorders by Common Mental Disorders—Screening Questionnaire. In Phase 2, a subgroup of Phase 1, 337 individuals were diagnosed by means of Present State Examination. Compensation for non-participation was carried out by multiple imputation by the use of data known for all sick-listed individuals from public registers. Results: The frequencies of mental disorders were: Any mental disorder 52%, depression 36%, anxiety 15%, somatoform disorder 7%, alcohol and drug dependence 6%, and personality disorder 6%. The diagnostic frequencies were highest for non-participants, female gender, age below 40 years, urban areas, single status, higher education, high skills/ managers, without a job, and low income. Conclusion: The prevalence of mental disorders among incident individuals on LSA was found to be about 50%. The burden on society may be higher than expected from previous studies solely based on participants as the methods compensating for missing values in this study indicated that the frequency of mental disorders was higher among non-participants than among participants.
Reframing political violence and mental health outcomes: outlining a research and action agenda for Latin America and the Caribbean region
Ciência & Saúde Coletiva , 2006, DOI: 10.1590/S1413-81232006000200008
Abstract: in recent decades, the number of people exposed to traumatic events has significantly increased as various forms of violence, including war and political upheaval, engulf civilian populations worldwide. in spite of widespread armed conflict, guerrilla warfare and political violence in the latin american and caribbean region, insufficient attention had been paid in assessing the medium and long-term psychological impact and additional burden of disease, death, and disability caused by violence and wars amongst civilian populations. following a review of the literature, a few central questions are raised: what is the short, medium and long-term health impact of extreme and sustained forms of violence in a given population? how political violence is linked to poor mental health outcomes at the individual and collective levels? are trauma-related disorders, universal outcomes of extreme and sustained violence? these questions lead us to reframe the analysis of political violence and mental health outcomes, and reexamine the notions of trauma, after which a research and action agenda for the region is outlined. in the concluding sections, some basic principles that may prove useful when designing psychosocial interventions in post-conflict situations are reviewed.
Page 1 /5677
Display every page Item

Copyright © 2008-2017 Open Access Library. All rights reserved.