3,137 research outputs found
A New Method for Multi-Bit and Qudit Transfer Based on Commensurate Waveguide Arrays
The faithful state transfer is an important requirement in the construction
of classical and quantum computers. While the high-speed transfer is realized
by optical-fibre interconnects, its implementation in integrated optical
circuits is affected by cross-talk. The cross-talk between densely packed
optical waveguides limits the transfer fidelity and distorts the signal in each
channel, thus severely impeding the parallel transfer of states such as
classical registers, multiple qubits and qudits. Here, we leverage on the
suitably engineered cross-talk between waveguides to achieve the parallel
transfer on optical chip. Waveguide coupling coefficients are designed to yield
commensurate eigenvalues of the array and hence, periodic revivals of the input
state. While, in general, polynomially complex, the inverse eigenvalue problem
permits analytic solutions for small number of waveguides. We present exact
solutions for arrays of up to nine waveguides and use them to design realistic
buses for multi-(qu)bit and qudit transfer. Advantages and limitations of the
proposed solution are discussed in the context of available fabrication
techniques
Anomalous thermopower and Nernst effect in : entropy-current loss in precursor state
The heavy-electron superconductor CeCoIn exhibits a puzzling precursor
state above its superconducting critical temperature at = 2.3 K. The
thermopower and Nernst signal are anomalous. Below 15 K, the entropy current of
the electrons undergoes a steep decrease reaching 0 at .
Concurrently, the off-diagonal thermoelectric current is
enhanced. The delicate sensitivity of the zero-entropy state to field implies
phase coherence over large distances. The prominent anomalies in the
thermoelectric current contrast with the relatively weak effects in the
resistivity and magnetization.Comment: 5 figures, 4 page
CoachNet: The further development of a coordinated network for sport coaching in Europe
Leeds Metropolitan University (LMU), in partnership with the European Coaching Council (ECC), was successful in a bid to the European Commission under the Preparatory Action in the Field of Sport (EAC/18/2011). The project was designed to develop an innovative approach that would contribute to the strengthening of the organisation of sport in Europe as part of the āgood governance, strand of the EU Preparatory Action in the Field of Sport. The primary objective was to examine ways in which the organisation of coaching could be enhanced in Europe, with a particular focus on the greater involvement of coaches in decisionmaking. In exploring ways to maximise the āvoice of the coachā, the partnership between LMU and ECC was central to the project. ECC is the continental division of the International Council for Coaching Excellence (ICCE). Through its network, ECC was in a position to identify current organisational arrangements for coaching across Europe. LMU is a well established research and practice oriented university in the UK and played a lead role in coordinating the project and guiding the research methodology through its Sport Coaching and Physical Education (SCOPE) Research and Enterprise Centre. Varying arrangements for the development and management of coaching were observed through a study of European countries. Within this varied landscape, the representation of coaches was sporadic, ranging from no representative mechanism to a number of good practice examples that made provision for the tiered engagement of coaches depending on their role; sport and coaching status category. These examples included confederated models across sports; blended models across coaching status categories and single and multi-sport models for the engagement and representation of coaches. The study concluded that there is a need for a more considered approach to the involvement of coaches in decision-making, with a number of recommendations developed for consideration by member states and the European divisions of the International Federations. These recommendations proposed that the structure of ECC as the European arm of ICCE be reviewed, with the intention to more strongly engage organisations that have been established to represent the voice of coaches and leading to a re-structuring of the organisation. In this context, ICCE and ECC should play an even stronger advocacy, representative and action role in establishing coaching as a blended profession, which includes volunteer, part-time paid and full-time paid coaches. More coherent structures for the engagement of coaches in each sport and country are also recommended. This should occur as part of a wider commitment that the principle of listening to and hearing the voice of the coach should become more strongly embedded within the way in which sporting and related organisations operate. The EU is well placed to lead on this type of approach, ensuring the coaches are more fully engaged in social dialogue and in the process to further enhance the role of sport and coaching in Europe. Further research is also recommended on the nature, needs and demographics of the coaching workforce. All of these approaches need to be tempered with the realisation that coaches are individual decision-makers, operating in a wide variety of contexts and many of whom do not show a propensity for involvement in formal ārepresentativeā structures. The need for alternative methods to connect with and engage coaches was, therefore, identified. These include a more segmented approach to engaging with coaches, depending on their coaching role and status, as well as the utilisation of more informal modes of web-based communication to connect directly with coaches in their daily lives. In all existing and future scenarios, the key role of federations at the national and international level in seeking, activating and allocating financial and other resources to connect with and support their coaches was highlighted. The findings have been notified to ICCE for formal consideration, leading to changes in the ways in which the voice of the coach is more clearly represented within the work of the organisation. ICCE should continue to work closely with the EU Sport Unit to ensure that the recommendations of this report are implemented and evaluated on an on-going basis
The Lorenz number in CeCoIn inferred from the thermal and charge Hall currents
The thermal Hall conductivity and Hall conductivity
in CeCoIn are used to determine the Lorenz number at low temperature . This enables the separation of the observed
thermal conductivity into its electronic and non-electronic parts. We uncover
evidence for a charge-neutral, field-dependent thermal conductivity, which we
identify with spin excitations. At low , these excitations dominate the
scattering of charge carriers. We show that suppression of the spin excitations
in high fields leads to a steep enhancement of the electron mean-free-path,
which leads to an interesting scaling relation between the magnetoresistance,
thermal conductivity and .Comment: 6 pages, 7 figures Intro para slightly lengthened. Added 2 new re
Composite localized modes in discretized spin-orbit-coupled Bose-Einstein condensates
We introduce a discrete model for binary spin-orbit-coupled (SOC)
Bose-Einstein condensates (BEC) trapped in a deep one-dimensional optical
lattice. Two different types of the couplings are considered, with spatial
derivatives acting inside each species, or between the species. The discrete
system with inter-site couplings dominated by the SOC, while the usual hopping
is negligible, \textit{emulates} condensates composed of extremely heavy atoms,
as well as those with opposite signs of the effective atomic masses in the two
components.\ Stable localized composite states of miscible and immiscible types
are constructed. The effect of the SOC on the immiscibility-miscibility
transition in the localized complexes, which emulates the phase transition
between insulating and conducting states in semiconductors, is studied.Comment: Journal of Physics B , in pres
Kondo Insulator description of spin state transition in FeSb2
The thermal expansion and heat capacity of FeSb2 at ambient pressure agrees
with a picture of a temperature induced spin state transition within the Fe
t_{2g} multiplet. However, high pressure powder diffraction data show no sign
of a structural phase transition up to 7GPa. A bulk modulus B=84(3)GPa has been
extracted and the temperature dependence of the Gruneisen parameter has been
determined. We discuss here the relevance of a Kondo insulator description for
this material.Comment: Physical Review B in press (2005
Direct Evidence for a Magnetic f-electron Mediated Cooper Pairing Mechanism of Heavy Fermion Superconductivity in CeCoIn5
To identify the microscopic mechanism of heavy-fermion Cooper pairing is an
unresolved challenge in quantum matter studies; it may also relate closely to
finding the pairing mechanism of high temperature superconductivity.
Magnetically mediated Cooper pairing has long been the conjectured basis of
heavy-fermion superconductivity but no direct verification of this hypothesis
was achievable. Here, we use a novel approach based on precision measurements
of the heavy-fermion band structure using quasiparticle interference (QPI)
imaging, to reveal quantitatively the momentum-space (k-space) structure of the
f-electron magnetic interactions of CeCoIn5. Then, by solving the
superconducting gap equations on the two heavy-fermion bands
with these magnetic interactions as mediators of the
Cooper pairing, we derive a series of quantitative predictions about the
superconductive state. The agreement found between these diverse predictions
and the measured characteristics of superconducting CeCoIn5, then provides
direct evidence that the heavy-fermion Cooper pairing is indeed mediated by the
f-electron magnetism.Comment: 19 pages, 4 figures, Supplementary Information: 31 pages, 5 figure
Coexistence of magnetism and superconductivity in CeRh1-xIrxIn5
We report a thermodynamic and transport study of the phase diagram of
CeRh1-xIrxIn5. Superconductivity is observed over a broad range of doping, 0.3
< x < 1, including a substantial range of concentration (0.3 < x <0.6) over
which it coexists with magnetic order (which is observed for 0 < x < 0.6). The
anomalous transition to zero resistance that is observed in CeIrIn5 is robust
against Rh substitution. In fact, the observed bulk Tc in CeRh0.5Ir0.5In5 is
more than double that of CeIrIn5, whereas the zero-resistance transition
temperature is relatively unchanged for 0.5 < x < 1
The Missing Link: Magnetism and Superconductivity
The effect of magnetic moments on superconductivity has long been a
controversial subject in condensed matter physics. While Matthias and
collaborators experimentally demonstrated the destruction of superconductivity
in La by the addition of magnetic moments (Gd), it has since been suggested
that magnetic fluctuations are in fact responsible for the development of
superconducting order in other systems. Currently this debate is focused on
several families of unconventional superconductors including high-Tc cuprates,
borocarbides as well as heavy fermion systems where magnetism and
superconductivity are known to coexist. Here we report a novel aspect of
competition and coexistence of these two competing orders in an interesting
class of heavy fermion compounds, namely the 1-1-5 series: CeTIn5 where T=Co,
Ir, or Rh. Our optical experiments indicate the existence of regions in
momentum space where local moments remain unscreened. The extent of these
regions in momentum space appears to control both the normal and
superconducting state properties in the 1-1-5 family of heavy fermion (HF)
superconductors.Comment: 6 pages, 2 figure
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