Measurement of geometric phase for mixed states using single photon interferometry

Geometric phase may enable inherently fault-tolerant quantum computation. However, due to potential decoherence effects, it is important to understand how such phases arise for mixed input states. We report the first experiment to measure mixed-state geometric phases in optics, using a Mach-Zehnder interferometer, and polarization mixed states that are produced in two different ways: decohering pure states with birefringent elements; and producing a nonmaximally entangled state of two photons and tracing over one of them, a form of remote state preparation.     

Generation of hyperentangled photon pairs

We experimentally demonstrate the first quantum system entangled in every degree of freedom (hyperentangled). Using pairs of photons produced in spontaneous parametric down-conversion, we verify entanglement by observing a Bell-type inequality violation in each degree of freedom: polarization, spatial mode, and time energy. We also produce and characterize maximally hyperentangled states and novel states simultaneously exhibiting both quantum and classical correlations. Finally, we report the tomography of a 2 x 2 x 3 x 3 system (36-dimensional Hilbert space), which we believe is the first reported photonic entangled system of this size to be so characterized.     

Microbial adhesion to poly(ethylene oxide) brushes: influence of polymer chain length and temperature

Glass surfaces were modified by end-grafting poly(ethylene oxide) (PEO) chains having molecular weights of 526, 2000, or 9800 Da. Characterization using water contact angles, ellipsometry, and X-ray photoelectron spectroscopy confirmed the presence of the PEO brushes on the surface with estimated lengths in water of 2.8-, 7.5-, and 23.7-nm, respectively. Adhesion of two bacterial (Staphylococcus epidermidis and Pseudomonas aeruginosa) and two yeast (Candida albicans and Candida tropicalis) strains to these brushes was studied and compared to their adhesion to bare glass. For the bacterium P. aeruginosa and the yeast C. tropicalis, adhesion to the 2.8-nm brush was comparable to their adhesion on bare glass, whereas adhesion to the 7.5- and 23.7-nm brushes was greatly reduced. For S. epidermidis, adhesion was only slightly higher to the 2.8-nm brush than that to the longer brushes. Adhesion of the yeast C. albicans to the PEO brushes was lower than that to glass, but no differences in adhesion were found between the three brush lengths. After passage of an air bubble, nearly all microorganisms adhering to a brush were removed, irrespective of brush length, whereas retention of the adhering organisms on glass was much higher. No significant differences were found in adhesion nor retention between experiments conducted at 20 and those conducted at 37 degrees C.     

Pitch of amplitude-modulated irregular-rate stimuli in acoustic and electric hearing

The pitch of stimuli was studied under conditions where place-of-excitation was held constant, and where pitch was therefore derived from "purely temporal" cues. In experiment 1, the acoustical and electrical pulse trains consisted of pulses whose amplitudes alternated between a high and a low value, and whose interpulse intervals alternated between 4 and 6 ms. The attenuated pulses occurred after the 4-ms intervals in condition A, and after the 6-ms intervals in condition B. For both normal-hearing subjects and cochlear implantees, the period of an isochronous pulse train equal in pitch to this "4-6" stimulus increased from near 6 ms at the smallest modulation depth to nearly 10 ms at the largest depth. Additionally, the modulated pulse trains in condition A were perceived as being lower in pitch than those in condition B. Data are interpreted in terms of increased refractoriness in condition A, where the larger pulses are more closely followed by the smaller ones than in condition B. Consistent with this conclusion, the A-B difference was reduced at longer interpulse intervals. These findings provide a measure of supra-threshold effects of refractoriness on pitch perception, and increase our understanding of coding of temporal information in cochlear implant speech processing schemes.     

An equivariant Brauer semigroup and the symmetric imprimitivity theorem

Suppose that is a second countable locally compact transformation group. We let denote the set of Morita equivalence classes of separable dynamical systems where is a -algebra and is compatible with the given -action on . We prove that is a commutative semigroup with identity with respect to the binary operation for an appropriately defined balanced tensor product on -algebras. If and act freely and properly on the left and right of a space , then we prove that and are isomorphic as semigroups. If the isomorphism maps the class of to the class of , then is Morita equivalent to .

     

Unraveling the dynamics of the C(3P,1D) + C2H2 reactions by the crossed molecular beam scattering technique

A detailed investigation of the dynamics of the reactions of ground- and excited-state carbon atoms, C(3P) and C(1D), with acetylene is reported over a wide collision energy range (3.6-49.1 kJ mol-1) using the crossed molecular beam (CMB) scattering technique with electron ionization mass spectrometric detection and time-of-flight (TOF) analysis. We have exploited the capability of (a) generating continuous intense supersonic beams of C(3P, 1D), (b) crossing the two reactant beams at different intersection angles (45, 90, and 135 degrees ) to attain a wide range of collision energies, and (c) tuning the energy of the ionizing electrons to low values (soft ionization) to suppress interferences from dissociative ionization processes. From angular and TOF distribution measurements of products at m/z=37 and 36, the primary reaction products of the C(3P) and C(1D) reactions with C2H2 have been identified to be cyclic (c)-C3H + H, linear (l)-C3H + H, and C3 + H2. From the data analysis, product angular and translational energy distributions in the center-of-mass (CM) system for both the linear and cyclic C3H isomers as well as the C3 product from C(3P) and for l/c-C3H and C3 from C(1D) have been derived as a function of collision energy from 3.6 to 49.1 kJ mol-1. The cyclic/linear C3H ratio and the C3/(C3 + c/l-C3H) branching ratios for the C(3P) reaction have been determined as a function of collision energy. The present findings have been compared with those from previous CMB studies using pulsed beams; here, a marked contrast is noted in the CM angular distributions for both C3H- and C3-forming channels from C(3P) and their trend with collision energy. Consequently, the interpretation of the reaction dynamics derived in the present work contradicts that previously proposed from the pulsed CMB studies. The results have been discussed in the light of the available theoretical information on the relevant triplet and singlet C3H2 ab initio potential energy surfaces (PESs). In particular, the branching ratios for the C(3P) + C2H2 reaction have been compared with the available theoretical predictions (approximate quantum scattering calculations and quasiclassical trajectory calculations on ab initio triplet PESs and, very recent, statistical calculations on ab initio triplet PESs as well as on ab initio triplet/singlet PESs including nonadiabatic effects, that is, intersystem crossing). While the experimental branching ratios have been corroborated by the statistical predictions, strong disagreement has been found with the results of the dynamical calculations. The astrophysical implications of the present results have been noted.     

π0-production in12C+12C at 800 and 1000 MeV/u

⁰-production in the system¹²C+¹²C was studied with the two-arm photon spectrometer TAPS at projectile energies of 800 and 1000 MeV/u. The experiments focus on the determination of the cross sections and the correspondingp _t -distributions. The results will extend the existing systematics of ⁰-production in heavy-ion collisions to a system with small mass.Presented at the International School-Workshop Relativistic Heavy-Ion Physics, Prague (Czech Republic), 19–23 September 1994.