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

Quantum Nonlocality in Two-Photon Experiments at Berkeley

We review some of our experiments performed over the past few years on two-photon interference. These include a test of Bell's inequalities, a study of the complementarity principle, an application of EPR correlations for dispersion-free time-measurements, and an experiment to demonstrate the superluminal nature of the tunneling process. The nonlocal character of the quantum world is brought out clearly by these experiments. As we explain, however, quantum nonlocality is not inconsistent with Einstein causality.Comment: 16 pages including 24 figure

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

Type 2 solar radio events observed in the interplanetary medium. Part 1: General characteristics

Twelve type 2 solar radio events were observed in the 2 MHz to 30 kHz frequency range by the radio astronomy experiment on the ISEE-3 satellite over the period from September 1978 to December 1979. These data provide the most comprehensive sample of type 2 radio bursts observed at kilometer wavelengths. Dynamic spectra of a number of events are presented. Where possible, the 12 events were associated with an initiating flare, ground based radio data, the passage of a shock at the spacecraft, and the sudden commencement of a geomagnetic storm. The general characteristics of kilometric type 2 bursts are discussed

Observation of high-order quantum resonances in the kicked rotor

Quantum resonances in the kicked rotor are characterized by a dramatically increased energy absorption rate, in stark contrast to the momentum localization generally observed. These resonances occur when the scaled Planck's constant hbar=(r/s)*4pi, for any integers r and s. However only the hbar=r*2pi resonances are easily observable. We have observed high-order quantum resonances (s>2) utilizing a sample of low temperature, non-condensed atoms and a pulsed optical standing wave. Resonances are observed for hbar=(r/16)*4pi r=2-6. Quantum numerical simulations suggest that our observation of high-order resonances indicates a larger coherence length than expected from an initially thermal atomic sample

Quasi-Particle Degrees of Freedom versus the Perfect Fluid as Descriptors of the Quark-Gluon Plasma

The hot nuclear matter created at the Relativistic Heavy Ion Collider (RHIC) has been characterized by near-perfect fluid behavior. We demonstrate that this stands in contradiction to the identification of QCD quasi-particles with the thermodynamic degrees of freedom in the early (fluid) stage of heavy ion collisions. The empirical observation of constituent quark ``$n_q$'' scaling of elliptic flow is juxtaposed with the lack of such scaling behavior in hydrodynamic fluid calculations followed by Cooper-Frye freeze-out to hadrons. A ``quasi-particle transport'' time stage after viscous effects break down the hydrodynamic fluid stage, but prior to hadronization, is proposed to reconcile these apparent contradictions. However, without a detailed understanding of the transitions between these stages, the ``$n_q$'' scaling is not a necessary consequence of this prescription. Also, if the duration of this stage is too short, it may not support well defined quasi-particles. By comparing and contrasting the coalescence of quarks into hadrons with the similar process of producing light nuclei from nucleons, it is shown that the observation of ``$n_{q}$'' scaling in the final state does not necessarily imply that the constituent degrees of freedom were the relevant ones in the initial state.Comment: 9 pages, 7 figures, Updated text and figure

Elastic turbulence in curvilinear flows of polymer solutions

Following our first report (A. Groisman and V. Steinberg, \sl Nature $\bf 405$, 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

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

An evaluation of the assessment tool used for extensive mini-dissertations in the Master’s Degree in Family Medicine, University of the Free State

Background: Family Medicine became a speciality in South Africa in 2007. Postgraduate studies in Family Medicine changed from part-time Master of Family Medicine (MFamMed) to a full-time Master of Medicine (Family Medicine) [MMed(Fam)] degree, with changes in the curriculum and assessment criteria. The overall goal of this study was to evaluate the current assessment tool for extensive mini-dissertations in the  postgraduate programme for Family Medicine, at the University of the Free State, and if necessary, to produce a valid and reliable assessment tool that is user-friendly.Method: An action research approach was used in this study, using mixed methods. Firstly, marks given by 15 assessors for four mini-dissertations using the current assessment tool were analysed quantitatively. In Phase 2, the regulation of the assessment bodies and the quantitative results of Phase 1 were discussed by assessors during a focus group interview, and data were analysed qualitatively. An adapted, improved assessment tool (Phase 3) was developed and re-evaluated in Phase 4.Results: The current assessment tool complied with the regulations of the assessment bodies. The scores allocated to specific categories varied with a median coefficient of variation of more than 15% in four of the possible 12 assessment categories. During the focus group interview, reasons for this were identified and the assessment tool adapted accordingly. During reassessment of the tool, individual assessors were identified as the  reason for poor reliability.Conclusion: The current assessment tool was found to be valid, but was not reliable for all assessment categories. The adapted assessment tool  addressed these areas, but identified lack of training and experience in the assessment of extensive mini-dissertations by certain assessors as the main reason for unreliable assessment

Conditional probabilities in quantum theory, and the tunneling time controversy

It is argued that there is a sensible way to define conditional probabilities in quantum mechanics, assuming only Bayes's theorem and standard quantum theory. These probabilities are equivalent to the ``weak measurement'' predictions due to Aharonov {\it et al.}, and hence describe the outcomes of real measurements made on subensembles. In particular, this approach is used to address the question of the history of a particle which has tunnelled across a barrier. A {\it gedankenexperiment} is presented to demonstrate the physically testable implications of the results of these calculations, along with graphs of the time-evolution of the conditional probability distribution for a tunneling particle and for one undergoing allowed transmission. Numerical results are also presented for the effects of loss in a bandgap medium on transmission and on reflection, as a function of the position of the lossy region; such loss should provide a feasible, though indirect, test of the present conclusions. It is argued that the effects of loss on the pulse {\it delay time} are related to the imaginary value of the momentum of a tunneling particle, and it is suggested that this might help explain a small discrepancy in an earlier experiment.Comment: 11 pages, latex, 4 postscript figures separate (one w/ 3 parts