Sample Abstracts
Measurement of Hurst Exponents for Semiconductor Laser Phase Dynamics
Wing-Shun Lam,1,2 Will Ray,1,2 Parvez N. Guzdar,2 and Rajarshi Roy1,2,3
1Department of Physics, University of Maryland, College Park, Maryland 20742, USA
2IREAP, University of Maryland, College Park, Maryland 20742, USA
3IPST, University of Maryland, College Park, Maryland 20742, USA
(Received 6 August 2004; published 3 January 2005)
The phase dynamics of a semiconductor laser with optical feedback is studied by construction of the Hilbert phase from its experimentally measured intensity time series. The Hurst exponent is evaluated for the phase fluctuations and grows from 0.5 to ~0.7 (indicating fractional Brownian motion) as the feedback strength is increased. A comparison with numerical computations based on a delay-differential equation model shows excellent agreement and reveals the relative roles of spontaneous emission noise and deterministic dynamics for different feedback strengths. ©2005 The American Physical Society
Temporal Dynamics of Photon Pairs Generated by an Atomic Ensemble
S. V. Polyakov, C. W. Chou, D. Felinto, and H. J. Kimble
Norman Bridge Laboratory of Physics 12-33, California Institute of Technology, Pasadena, California 91125, USA
(Received 4 June 2004; published 20 December 2004)
The time dependence of nonclassical correlations is investigated for two fields (1,2) generated by an ensemble of cold cesium atoms via the protocol of Duan etal. [Nature (London) 414, 413 (2001)]. The correlation function R(t1,t2) for the ratio of cross to autocorrelations for the (1,2) fields at times (t1,t2) is found to have a maximum value Rmax = 292±57, which significantly violates the Cauchy-Schwarz inequality R1 for classical fields. Decoherence of quantum correlations is observed over d175 ns, and is described by our model, as is a new scheme to mitigate this effect. ©2004 The American Physical Society
New Phase Diagram of Oxygen at High Pressures and Temperatures
Mario Santoro,1,2 Eugene Gregoryanz,1 Ho-kwang Mao,1 and Russell J. Hemley1
1Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road N.W., Washington, D.C. 20015 USA
2LENS, European Laboratory for Non-linear Spectroscopy and INFM, Via Carrara 1, I-50019 Sesto Fiorentino, Firenze, Italy
(Received 21 April 2004; published 20 December 2004)
Insitu high P-T Raman measurements and optical observations of solid and fluid oxygen up to 1250K between 8 and 25GPa reveal the existence of a new molecular phase and strikingly unusual behavior of the melting curve. Three triple points were also identified in the P-T domain of the new phase. The data give a direct measure of the melting curve that greatly extends previous optical investigations. We find the melting temperature is significantly higher than that indicated by the existing phase diagram (e.g., 400K higher at 25GPa). Raman measurements in low and high frequency regions reveal the extent of orientational order disorder and persistence of strong intermolecular interactions in the high P-T phases. ©2004 The American Physical Society
Disorder-Induced Polaron Formation in the Magnetoresistive Perovskite La0.54Ba0.46MnO3
T. J. Sato,1 J. W. Lynn,1 and B. Dabrowski2
1NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-8562, USA
2Department of Physics, Northern Illinois University, DeKalb, Illinois 60115, USA
(Received 9 January 2004; published 27 December 2004)
Neutron studies of the effect of A-site chemical disorder on the ferromagnetic transition and spin dynamics for the magnetoresistive perovskite La0.54Ba0.46MnO3 are reported. The low temperature spin waves reveal that disorder reduces exchange interactions by only 9%. The development of a quasielastic peak in the spectrum below TC and long-time relaxation of the order parameter indicate that the transition is discontinuous in the disordered sample, while it appears continuous for the ordered sample. These results strongly suggest that chemical disorder lowers the energy for polaron formation in manganese perovskites, and is the origin of the dramatic 50K reduction in TC. ©2004 The American Physical Society