10,673 research outputs found
Extracting joint weak values with local, single-particle measurements
Weak measurement is a new technique which allows one to describe the
evolution of postselected quantum systems. It appears to be useful for
resolving a variety of thorny quantum paradoxes, particularly when used to
study properties of pairs of particles. Unfortunately, such nonlocal or joint
observables often prove difficult to measure weakly in practice (for instance,
in optics -- a common testing ground for this technique -- strong photon-photon
interactions would be needed). Here we derive a general, experimentally
feasible, method for extracting these values from correlations between
single-particle observables.Comment: 6 page
Comment on "A linear optics implementation of weak values in Hardy's paradox"
A recent experimental proposal by Ahnert and Payne [S.E. Ahnert and M.C.
Payne, Phys. Rev. A 70, 042102 (2004)] outlines a method to measure the weak
value predictions of Aharonov in Hardy's paradox. This proposal contains flaws
such as the state preparation method and the procedure for carrying out the
requisite weak measurements. We identify previously published solutions to some
of the flaws.Comment: To be published in Physical Review
Rank 3 permutation characters and maximal subgroups
In this paper we classify all maximal subgroups M of a nearly simple
primitive rank 3 group G of type L=Omega_{2m+1}(3), m > 3; acting on an L-orbit
E of non-singular points of the natural module for L such that 1_P^G <=1_M^G
where P is a stabilizer of a point in E. This result has an application to the
study of minimal genera of algebraic curves which admit group actions.Comment: 41 pages, to appear in Forum Mathematicu
Mixing by polymers: experimental test of decay regime of mixing
By using high molecular weight fluorescent passive tracers with different
diffusion coefficients and by changing the fluid velocity we study dependence
of a characteristic mixing length on the Peclet number, , which controls
the mixing efficiency. The mixing length is found to be related to by a
power law, , and increases faster than
expected for an unbounded chaotic flow. Role of the boundaries in the mixing
length abnormal growth is clarified. The experimental findings are in a good
quantitative agreement with the recent theoretical predictions.Comment: 4 pages,5 figures. accepted for publication in PR
Neural mechanisms of resistance to peer influence in early adolescence
During the shift from a parent-dependent child to a fully autonomous adult, peers take on a significant role in shaping the adolescent’s behaviour. Peer-derived influences are not always positive, however. Here we explore neural correlates of inter-individual differences in the probability of resisting peer influence in early adolescence. Using functional magnetic-resonance imaging (fMRI), we found striking differences between 10-year old children with high and low resistance to peer influence in their brain activity during observation of angry hand-movements and angry facial expressions: compared with subjects with low resistance to peer influence, individuals with high resistance showed a highly coordinated brain activity in neural systems underlying perception of action and decision making. These findings suggest that the probability of resisting peer influence depends on neural interactions during observation of emotion-laden actions
Elastic turbulence in curvilinear flows of polymer solutions
Following our first report (A. Groisman and V. Steinberg, \sl Nature , 53 (2000)) we present an extended account of experimental observations of
elasticity induced turbulence in three different systems: a swirling flow
between two plates, a Couette-Taylor (CT) flow between two cylinders, and a
flow in a curvilinear channel (Dean flow). All three set-ups had high ratio of
width of the region available for flow to radius of curvature of the
streamlines. The experiments were carried out with dilute solutions of high
molecular weight polyacrylamide in concentrated sugar syrups. High polymer
relaxation time and solution viscosity ensured prevalence of non-linear elastic
effects over inertial non-linearity, and development of purely elastic
instabilities at low Reynolds number (Re) in all three flows. Above the elastic
instability threshold, flows in all three systems exhibit features of developed
turbulence. Those include: (i)randomly fluctuating fluid motion excited in a
broad range of spatial and temporal scales; (ii) significant increase in the
rates of momentum and mass transfer (compared to those expected for a steady
flow with a smooth velocity profile). Phenomenology, driving mechanisms, and
parameter dependence of the elastic turbulence are compared with those of the
conventional high Re hydrodynamic turbulence in Newtonian fluids.Comment: 23 pages, 26 figure
Two Decades Of Pelagic Ecology Of The Western Antarctic Peninsula
Significant strides in our understanding of the marine pelagic ecosystem of the Western Antarctic Peninsula (WAP) region have been made over the past two decades, resulting from research conducted aboard ARSV Laurence M. Gould and RVIB Nathaniel B. Palmer. These advances range from an understanding of the physical forcing on biology, to food web ecology (from microbes to top predators), to biogeochemical cycling, often in the larger context of rapid climate warming in the region. The proximity of the WAP to the Antarctic Circumpolar Current and WAP continental shelf bathymetry affects the hydrography and helps structure the biological community. Seasonal, spatial, and interannual variability at all levels of the food web, as well as the mechanisms supporting their production, are now more clearly understood. New tools and technologies employed in the region were critical for making this research possible. As a result, our knowledge of the WAP pelagic ecosystem during a time of rapid climate change has vastly improved
Sub-femtosecond determination of transmission delay times for a dielectric mirror (photonic bandgap) as a function of angle of incidence
Using a two-photon interference technique, we measure the delay for
single-photon wavepackets to be transmitted through a multilayer dielectric
mirror, which functions as a ``photonic bandgap'' medium. By varying the angle
of incidence, we are able to confirm the behavior predicted by the group delay
(stationary phase approximation), including a variation of the delay time from
superluminal to subluminal as the band edge is tuned towards to the wavelength
of our photons. The agreement with theory is better than 0.5 femtoseconds (less
than one quarter of an optical period) except at large angles of incidence. The
source of the remaining discrepancy is not yet fully understood.Comment: 5 pages and 5 figure
Quantum nonlocality obtained from local states by entanglement purification
We have applied an entanglement purification protocol to produce a single
entangled pair of photons capable of violating a CHSH Bell inequality from two
pairs that individually could not. The initial poorly-entangled photons were
created by a controllable decoherence that introduced complex errors. All of
the states were reconstructed using quantum state tomography which allowed for
a quantitative description of the improvement of the state after purification.Comment: 4 pages, 4 figure
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