16,094 research outputs found
Scattering of second sound waves by quantum vorticity
A new method of detection and measurement of quantum vorticity by scattering
second sound off quantized vortices in superfluid Helium is suggested.
Theoretical calculations of the relative amplitude of the scattered second
sound waves from a single quantum vortex, a vortex ring, and bulk vorticity are
presented. The relevant estimates show that an experimental verification of the
method is feasible. Moreover, it can even be used for the detection of a single
quantum vortex.Comment: Latex file, 9 page
Fault-tolerant linear optical quantum computing with small-amplitude coherent states
Quantum computing using two optical coherent states as qubit basis states has
been suggested as an interesting alternative to single photon optical quantum
computing with lower physical resource overheads. These proposals have been
questioned as a practical way of performing quantum computing in the short term
due to the requirement of generating fragile diagonal states with large
coherent amplitudes. Here we show that by using a fault-tolerant error
correction scheme, one need only use relatively small coherent state amplitudes
() to achieve universal quantum computing. We study the effects
of small coherent state amplitude and photon loss on fault tolerance within the
error correction scheme using a Monte Carlo simulation and show the quantity of
resources used for the first level of encoding is orders of magnitude lower
than the best known single photon scheme. %We study this reigem using a Monte
Carlo simulation and incorporate %the effects of photon loss in this
simulation
Star-Like Micelles with Star-Like Interactions: A quantitative Evaluation of Structure Factor and Phase Diagram
PEP-PEO block copolymer micelles offer the possibility to investigate phase
behaviour and interactions of star polymers (ultra-soft colloids). A star-like
architecture is achieved by an extremely asymmetric block ratio (1:20).
Micellar functionality f can be smoothly varied by changing solvent composition
(interfacial tension). Structure factors obtained by SANS can be quantitatively
described in terms of an effective potential developed for star polymers. The
experimental phase diagram reproduces to a high level of accuracy the predicted
liquid/solid transition. Whereas for intermediate f a bcc phase is observed,
for high f the formation of a fcc phase is preempted by glass formation.Comment: 5 pages, 4 figures, PRL in pres
Topological Landau-Ginzburg Theory for Vortices in Superfluid He
We propose a new Landau-Ginzburg theory for arbitrarily shaped vortex strings
in superfluid He. The theory contains a topological term and directly
describes vortex dynamics. We introduce gauge fields in order to remove
singularities from the Landau-Ginzburg order parameter of the superfluid, so
that two kinds of gauge symmetries appear, making the continuity equation and
conservation of the total vorticity manifest. The topological term gives rise
to the Berry phase term in the vortex mechanical actions.Comment: LATEX, 9 page
Effective slip boundary conditions for flows over nanoscale chemical heterogeneities
We study slip boundary conditions for simple fluids at surfaces with
nanoscale chemical heterogeneities. Using a perturbative approach, we examine
the flow of a Newtonian fluid far from a surface described by a heterogeneous
Navier slip boundary condition. In the far-field, we obtain expressions for an
effective slip boundary condition in certain limiting cases. These expressions
are compared to numerical solutions which show they work well when applied in
the appropriate limits. The implications for experimental measurements and for
the design of surfaces that exhibit large slip lengths are discussed.Comment: 14 pages, 3 figure
Measuring measurement--disturbance relationships with weak values
Using formal definitions for measurement precision {\epsilon} and disturbance
(measurement backaction) {\eta}, Ozawa [Phys. Rev. A 67, 042105 (2003)] has
shown that Heisenberg's claimed relation between these quantities is false in
general. Here we show that the quantities introduced by Ozawa can be determined
experimentally, using no prior knowledge of the measurement under investigation
--- both quantities correspond to the root-mean-squared difference given by a
weak-valued probability distribution. We propose a simple three-qubit
experiment which would illustrate the failure of Heisenberg's
measurement--disturbance relation, and the validity of an alternative relation
proposed by Ozawa
Scattering of first and second sound waves by quantum vorticity in superfluid Helium
We study the scattering of first and second sound waves by quantum vorticity
in superfluid Helium using two-fluid hydrodynamics. The vorticity of the
superfluid component and the sound interact because of the nonlinear character
of these equations. Explicit expressions for the scattered pressure and
temperature are worked out in a first Born approximation, and care is exercised
in delimiting the range of validity of the assumptions needed for this
approximation to hold. An incident second sound wave will partly convert into
first sound, and an incident first sound wave will partly convert into second
sound. General considerations show that most incident first sound converts into
second sound, but not the other way around. These considerations are validated
using a vortex dipole as an explicitely worked out example.Comment: 24 pages, Latex, to appear in Journal of Low Temperature Physic
Experimental determination of the degree of quantum polarisation of continuous variable states
We demonstrate excitation-manifold resolved polarisation characterisation of
continuous-variable (CV) quantum states. In contrast to traditional
characterisation of polarisation that is based on the Stokes parameters, we
experimentally determine the Stokes vector of each excitation manifold
separately. Only for states with a given photon number does the methods
coincide. For states with an indeterminate photon number, for example Gaussian
states, the employed method gives a richer and more accurate description. We
apply the method both in theory and in experiment to some common states to
demonstrate its advantages.Comment: 5 page
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