Pressure-Induced Magnetic Quantum Phase Transitions from Gapped Ground State in TlCuCl3

Magnetization maesurements under hydrostatic pressure were performed on an S=1/2 coupled spin system TlCuCl3 with a gapped ground state under magnetic field H parallel to the [2,0,1] direction. With increasing applied pressure P, the gap decreases and closes completely at Pc=0.42 kbar. For P>Pc, TlCuCl3 undergoes antiferromagnetic ordering. A spin-flop transition was observed at Hsf=0.7T. The spin-flop field is approximately independent of pressure, although the sublattice magnetization increases with pressure. The gap and Neel temperature are presented as function is attributed to to the relative enhancement of the interdimer exchange interactions compared with the intradimer exchange interaction.Comment: 4pages,3figures To be published in J. Phys. Soc. Jpn. Vol.73 No.1

Hole-hole superconducting pairing in the t-J model induced by spin-wave exchange

We study numerically the hole pairing induced by spin-wave exchange. The contact hole-hole interaction is taken into account as well. It is assumed that antiferromagnetic order is preserved at all scales relevant to pairing. The strongest pairing is obtained for the d-wave symmetry of the gap. Dependence of the value of the gap on hole concentration and temperature is presented. For the critical temperature we obtain Tc about 100 K at the hole concentration delta = 0.2-0.3.Comment: replaced with a revised version to appear in PRB, 6 pages, REVTeX 3.0, figures not change

Ehrenfest relations and magnetoelastic effects in field-induced ordered phases

Magnetoelastic properties in field-induced magnetic ordered phases are studied theoretically based on a Ginzburg-Landau theory. A critical field for the field-induced ordered phase is obtained as a function of temperature and pressure, which determine the phase diagram. It is found that magnetic field dependence of elastic constant decreases discontinuously at the critical field, Hc, and that it decreases linearly with field in the ordered phase (H>Hc). We found an Ehrenfest relation between the field dependence of the elastic constant and the pressure dependence of critical field. Our theory provides the theoretical form for magnetoelastic properties in field- and pressure-induced ordered phases.Comment: 7 pages, 3 figure

Joint Elastic Side-Scattering Lidar and Raman Lidar Measurements of Aerosol Optical Properties in South East Colorado

We describe an experiment, located in south-east Colorado, USA, that measured aerosol optical depth profiles using two Lidar techniques. Two independent detectors measured scattered light from a vertical UV laser beam. One detector, located at the laser site, measured light via the inelastic Raman backscattering process. This is a common method used in atmospheric science for measuring aerosol optical depth profiles. The other detector, located approximately 40km distant, viewed the laser beam from the side. This detector featured a 3.5m2 mirror and measured elastically scattered light in a bistatic Lidar configuration following the method used at the Pierre Auger cosmic ray observatory. The goal of this experiment was to assess and improve methods to measure atmospheric clarity, specifically aerosol optical depth profiles, for cosmic ray UV fluorescence detectors that use the atmosphere as a giant calorimeter. The experiment collected data from September 2010 to July 2011 under varying conditions of aerosol loading. We describe the instruments and techniques and compare the aerosol optical depth profiles measured by the Raman and bistatic Lidar detectors.Comment: 34 pages, 16 figure

Pressure-Induced Magnetic Quantum Phase Transition in Gapped Spin System KCuCl3

Magnetization and neutron elastic scattering measurements under a hydrostatic pressure were performed on KCuCl3, which is a three-dimensionally coupled spin dimer system with a gapped ground state. It was found that an intradimer interaction decreases with increasing pressure, while the sum of interdimer interactions increases. This leads to the shrinkage of spin gap. A quantum phase transition from a gapped state to an antiferromagnetic state occurs at Pc ? 8.2 kbar. For P > P c, magnetic Bragg reflections were observed at reciprocal lattice points equivalent to those for the lowest magnetic excitation at zero pressure. This confirms that the spin gap decreases and closes under applied pressure.Comment: 7 pages, 10 figures, submitted to J. Phys. Soc. Jp

Spin gap behavior and charge ordering in \alpha^{\prime}-NaV_2O_5 probed by light scattering

We present a detailed analysis of light scattering experiments performed on the quarter-filled spin ladder compound $\alpha^\prime$-NaV$_{2}$O$_{5}$ for the temperature range 5 K$\le$T$\le$300 K. This system undergoes a phase transition into a singlet ground state at T=34 K accompanied by the formation of a super structure. For T$\leq$34 K several new modes were detected. Three of these modes are identified as magnetic bound states. Experimental evidence for charge ordering on the V sites is detected as an anomalous shift and splitting of a V-O vibration at 422 cm$^{-1}$ for temperatures above 34 K. The smooth and crossover-like onset of this ordering at T$_{\rm CO}$= 80 K is accompanied by pretransitional fluctuations both in magnetic and phononic Raman scattering. It resembles the effect of stripe order on the super structure intensities in La$_2$NiO$_{4+\delta}$.Comment: 36 pages, 11 figures, accepted for publication in PRB (sept.99

Generating entangled superpositions of macroscopically distinguishable states within a parametric oscillator

We suggest a variant of the recently proposed experiment for the generation of a new kind of Schroedinger-cat states, using two coupled parametric down-converter nonlinear crystals [F. De Martini, Phys. Rev. Lett. 81, 2842 (1998)]. We study the parametric oscillator case and find that an entangled Schroedinger-cat type state of two cavities, whose mirrors are placed along the output beams of the nonlinear crystals, can be realized under suitable conditions.Comment: RevTeX 17 pages, 9 eps files for 7 figures. Submitted to Physical Review

Hole-Hole Contact Interaction in the t-J Model

Using an analytical variational approach we calculate the hole-hole contact interaction on the N\'{e}el background. Solution of the Bethe-Salpeter equation with this interaction gives bound states in $d$- and p-waves with binding energies close to those obtained by numerical methods. At $t/J \ge 2-3$ the bound state disappears. In conclusion we discuss the relation between short range and long range interactions and analogy with the problem of pion condensation in nuclear matter.Comment: 11 pp. (LATEX), 7 figures (PostScript) appended, report N

Stabilization of Deterministically Chaotic Systems by Interference and Quantum Measurements: The Ikeda Map Case

We propose a method which can effectively stabilize fixed points in the classical and quantum dynamics of a phase-sensitive chaotic system with feedback. It is based on feeding back a selected quantum sub-ensemble whose phase and amplitude stabilize the otherwise chaotic dynamics. Although the method is rather general, we apply it to realizations of the inherently chaotic Ikeda map. One suggested realization involves the Mach-Zender interferometer with Kerr nonlinearity. Another realization involves a trapped ion interacting with laser fields.Comment: RevTeX, 5 pages, two figure