Biomedical subjects
Publications and source records attributed to P R Berman.
We show that the probability distributions for the number of Rydberg excitations in small ensembles of cold atoms, excited using short (100 ns) laser pulses, can be highly sub-Poissonian. The phenomenon occurs if the atom density and the principal quantum number of the excited Rydberg level are sufficiently high. Our observations are attributed to a blockade of the Rydberg atom excitation.
We report on the coherent optical excitation of electron spin polarization in the ground state of charged GaAs quantum dots via an intermediate charged exciton (trion) state. Coherent optical fields are used for the creation and detection of the Raman spin coherence between the spin ground states of the charged quantum dot. The measured spin decoherence time, which is likely limited by the nature of the spin ensemble, approaches 10 ns at zero field. We also show that the Raman spin coherence in the quantum beats is caused not only by the usual stimulated Raman interaction but also by simultaneous spontaneous radiative decay of either excited trion state to a coherent combination of the two spin states.
The electrostatic potential is calculated above a uniformly charged conducting plane that has been deformed to include a hemispherical cup centered at the origin. The charge density on the surface is obtained.
The coherence of two coupled two-level systems, representing vibrational modes in a semiclassical model, is calculated in weak and strong fields for various coupling schemes and for different relative phases between initial state amplitudes. A relative phase equal to pi projects the system into a dark state. The selective excitation of one of the two, two-level systems is studied as a function of coupling strength and initial phases.
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The modification of the radiative decay rate of a source atom embedded in a uniform, isotropic dielectric is calculated to first order in the density of the dielectric atoms using a microscopic approach. In contrast to the recent results of Crenshaw and Bowden [Phys. Rev. Lett. 85, 1851 (2000)]], the decay rate is found to be consistent with macroscopic theories based on quantization of the field in the dielectric.
The Goos-Hänchen shift is calculated when total internal reflection occurs at an interface between "normal" and negatively refractive media. The shift is negative, consistent with the direction of energy flow in the negatively refractive medium.
The abdominal ganglion of Aplysia californica was perfused with artificial seawater equilibrated at different P(COCO2)'s and pH's for 5 min or less. 5% CO(2) dropped perfusate pH from 8.0 to 6.5 and produced depolarization and increased discharge rate in visceromotor neurons. Half the giant cells studied had a similar response, whereas the other half were hyperpolarized. Pacemaker neurons showed little, if any, response to such changes in pH or CO(2). Membrane conductance of responsive cells was always increased. The effect of CO(2) occurred even when synaptic transmission was blocked by low calcium and high magnesium, and therefore must have been a direct result of CO(2) or the concomitant fall in pH. When extracellular pH was lowered to 6.5 using HCl or H(2)SO(4) and no CO(2), the same effects were observed. Also, local application of HCl or H(2)SO(4) to the external surface of the cell soma elicited depolarization and spike discharge. When extracellular pH was held constant by continual titration, 5-50% CO(2) had no effect. Intracellular pH was probably decreased at least one pH unit under these circumstances. Thus CO(2) per se, decreased intracellular pH, and increased bicarbonate ion were without effect. It is concluded that CO(2) acts solely through a decrease in extracellular pH.