3,765 research outputs found
Rotating quantum turbulence in superfluid 4He in the T=0 limit
Observations of quantum turbulence in pure superfluid 4He in a rotating
container are reported. New techniques of large-scale forcing (rotational
oscillations of the cubic container) and detecting (monitoring ion transport
along the axis of rotation) turbulence were implemented. Near the axial walls,
with increasing forcing the vortex tangle grows without an observable
threshold. This tangle gradually develops into bulk turbulence at a
characteristic amplitude of forcing that depends on forcing frequency and
rotation rate. At higher amplitudes, the total vortex line length increases
rapidly. Resonances of inertial waves are observed in both laminar and
turbulent bulk states. On such resonances, the turbulence appears at smaller
amplitudes of forcing.Comment: 5 pages, 5 figure
Entrepreneurial intentions among students: towards a re-focused research agenda
Purpose â This paper aims to address the need for a re-focused research agenda in relation to graduate entrepreneurship. An important theme for some years has been the effort to monitor attitudes and intentions of students towards starting up their own businesses. It is timely, however, to raise some questions about both the impact of this research and likewise the general approach it has taken in understanding the phenomenon of graduate entrepreneurship. Design/methodology/approach â The paper draws on a large data set (over 8,000 students) from one UK region. Specifically, it presents data from the 2007/2008 Entrepreneurial Intentions (EI) survey within the Yorkshire and Humberside region and reflects back over previous iterations of this research. Findings â The paper identifies three key outcomes. First, it establishes that across all years of the survey a substantial minority of students consistently hold relatively strong start-up intentions. Second, the paper highlights that, despite considerable efforts to increase the numbers moving to start-up, little impact is discernible. Third, the paper suggests that, although the EI survey is useful as a stock-taking exercise, it fails to address critical questions around the impact of higher education on entrepreneurship and the transition from entrepreneurial intent to the act of venture creation. Originality/value â The paper provides an important positioning perspective on the relationship between higher education and graduate entrepreneurship. While highlighting the importance of the EI research, the paper establishes the need for a re-focused research agenda; one that is conceptually robust and with a focus on the student journey from higher education to graduate entrepreneur
Chirality of superfluid 3He-A
We have used torsional oscillators, containing disk-shaped slabs of
superfluid 3He-A, to probe the chiral orbital textures created by cooling into
the superfluid state while continuously rotating. Comparing the observed
flow-driven textural transitions with numerical simulations of possible
textures shows that an oriented monodomain texture with l antiparallel to the
angular velocity Omega_0 is left behind after stopping rotation. The bias
towards a particular chirality, while in the vortex state, is due to the
inequivalence of energies of vortices of opposite circulation. When spun-up
from rest, the critical velocity for vortex nucleation depends on the sense of
rotation, Omega, relative to that of l. A different type of vorticity,
apparently linked to the slab's rim by a domain wall, appears when Omega is
parallel to l.Comment: 8 pages, 6 figure
Photon engineering for quantum information processing
We study distinguishing information in the context of quantum interference
involving more than one parametric downconversion (PDC) source and in the
context of polarization-entangled photon pairs based on PDC. We arrive at
specific design criteria for two-photon sources so that when used as part of
complex optical systems, such as photon-based quantum information processing
schemes, distinguishing information between the photons is eliminated
guaranteeing high visibility interference. We propose practical techniques
which lead to suitably engineered two-photon states that can be realistically
implemented with available technology. Finally, we study an implementation of
the nonlinear-sign shift (NS) logic gate with PDC sources and show the effect
of distinguishing information on the performance of the gate.Comment: 23 pages, 13 figures. submitted to Quantum Information & Computatio
Direct, Loss-Tolerant Characterization of Nonclassical Photon Statistics
We experimentally investigate a method of directly characterizing the photon
number distribution of nonclassical light beams that is tolerant to losses and
makes use only of standard binary detectors. This is achieved in a single
measurement by calibrating the detector using some small amount of prior
information about the source. We demonstrate the technique on a freely
propagating heralded two-photon number state created by conditional detection
of a two-mode squeezed state generated by a parametric downconverter.Comment: 5 pages, 2 figure
Precision metrology using weak measurements
Weak values and measurements have been proposed as means to achieve dramatic
enhancements in metrology based on the greatly increased range of possible
measurement outcomes. Unfortunately, the very large values of measurement
outcomes occur with highly suppressed probabilities. This raises three vital
questions in weak-measurement-based metrology, namely, (Q1) Does post-selection
enhance the measurement precision? (Q2) Does weak measurement offer better
precision than strong measurement? (Q3) Is it possible to beat the standard
quantum limit or to achieve the Heisenberg limit with weak measurement using
only classical resources? We analyse these questions for two prototypical, and
generic, measurement protocols and show that while the answers to the first two
questions are negative for both protocols, the answer to the last is
affirmative for measurements with phase-space interactions, and negative for
configuration space interactions. Our results, particularly the ability of weak
measurements to perform at par with strong measurements in some cases, are
instructive for the design of weak-measurement-based protocols for quantum
metrology.Comment: 5+5 pages, 2 figure
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