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

Flow induced ultrasound scattering: experimental studies

Sound scattering by a finite width beam on a single rigid body rotation vortex flow is detected by a linear array of transducers (both smaller than a flow cell), and analyzed using a revised scattering theory. Both the phase and amplitude of the scattered signal are obtained on 64 elements of the detector array and used for the analysis of velocity and vorticity fields. Due to averaging on many pulses the signal-to-noise ratio of the phases difference in the scattered sound signal can be amplified drastically, and the resolution of the method in the detection of circulation, vortex radius, vorticity, and vortex location becomes comparable with that obtained earlier by time-reversal mirror (TRM) method (P. Roux, J. de Rosny, M. Tanter, and M. Fink, {\sl Phys. Rev. Lett.} {\bf 79}, 3170 (1997)). The revised scattering theory includes two crucial steps, which allow overcoming limitations of the existing theories. First, the Huygens construction of a far field scattering signal is carried out from a signal obtained at any intermediate plane. Second, a beam function that describes a finite width beam is introduced, which allows using a theory developed for an infinite width beam for the relation between a scattering amplitude and the vorticity structure function. Structure functions of the velocity and vorticity fields deduced from the sound scattering signal are compared with those obtained from simultaneous particle image velocimetry (PIV) measurements. Good quantitative agreement is found.Comment: 14 pages, 23 figures. accepted for publication in Phys. Fluids(June issue

A low-mass faraday cup experiment for the solar wind

Faraday cups have proven to be very reliable and accurate instruments capable of making 3-D velocity distribution measurements on spinning or 3-axis stabilized spacecraft. Faraday cup instrumentation continues to be appropriate for heliospheric missions. As an example, the reductions in mass possible relative to the solar wind detection system about to be flown on the WIND spacecraft were estimated. Through the use of technology developed or used at the MIT Center for Space Research but were not able to utilize for WIND: surface-mount packaging, field-programmable gate arrays, an optically-switched high voltage supply, and an integrated-circuit power converter, it was estimated that the mass of the Faraday Cup system could be reduced from 5 kg to 1.8 kg. Further redesign of the electronics incorporating hybrid integrated circuits as well as a decrease in the sensor size, with a corresponding increase in measurement cycle time, could lead to a significantly lower mass for other mission applications. Reduction in mass of the entire spacecraft-experiment system is critically dependent on early and continual collaborative efforts between the spacecraft engineers and the experimenters. Those efforts concern a range of issues from spacecraft structure to data systems to the spacecraft power voltage levels. Requirements for flight qualification affect use of newer, lighter electronics packaging and its implementation; the issue of quality assurance needs to be specifically addressed. Lower cost and reduced mass can best be achieved through the efforts of a relatively small group dedicated to the success of the mission. Such a group needs a fixed budget and greater control over quality assurance requirements, together with a reasonable oversight mechanism

Experimental Investigation at M-20 of the Longitudinal Aerodynamic Characteristics, Pressure and Heat Transfer Distribution on a 50° Semivertex Angle Sphere-Cone

As part of continuing generalized overall space exploration studies, the Martin Company Space Exploration Group has been engaged in detailed study of the conceptual design of systems and configurations which ultimately would lead to development of a configuration suitable both for Mars atmosphere entry and landing an instrumented payload on the planet\u27s surface. A significant aspect of these Voyager Program Studies encompassed an experimental program devoted to obtaining detailed data concerning the aerodynamic characteristics, heat transfer, and pressure distributions on high-drag configurations at Mach numbers typical of atmospheric entry. One of our most comprehensive experimental efforts associated with the aerodynamics of atmospheric entry included investigations on a 50° semivertex angle sphere-cone equipped with varied afterbody shapes (Fig. 1 ). This configuration is the subject of this paper. It was specifically selected because it is representative of an applicable Voyager configuration and is a simple enough shape to permit comparison of the experimental results with those obtained by theoretical study. The facility utilized for these investigations was the Martin Company\u27s 25-in. Arc Heated Wind Tunnel 1 located at Middle River, Maryland. All the tests were conducted at a nominal Mach number of 20 in dry nitrogen, and data were obtained at environmental condi - tions which closely simulated portions of a typical deorbit trajectory of the Voyager Lander configuration as exemplified in Fig. 2. The trajectories superimposed on these plots are de-orbit mode trajectories into the Martian atmospheres commonly known as VM-7 and VM-8, which are based upon the Mariner N occultation experiment

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

Preparation of pure and mixed polarization qubits and the direct measurement of figures of merit

Non-classical joint measurements can hugely improve the efficiency with which certain figures of merit of quantum systems are measured. We use such a measurement to determine a particular figure of merit, the purity, for a polarization qubit. In the process we highlight some of subtleties involved in common methods for generating decoherence in quantum optics.Comment: 5 pages, 3 figures, 1 tabl