Steve Simon

Abstract:

The use of multi-antenna arrays has been predicted to provide substantial throughput gains for wireless communication systems. However, these predictions have to be assessed in realistic situations, such as correlated channels and in the presence of interference. In this review, we show results obtained using methods borrowed from statistical physics of random media for the average and the variance of the distribution of the mutual information of multi-antenna systems with arbitrary correlations and interferers. Even though the methods are asymptotic in the sense they are valid in the limit of large antenna numbers, the results are accurate even for small arrays. We also optimize over the input signal covariance with channel covariance feedback and calculate closed-loop capacities. This method provides a simple tool to analyze the statistics of throughput for arrays of any size.

Abstract:

We consider the design of two-dimensional electrostatic traps for dipolar indirect excitons. We show that the exciton dipole-dipole interaction, combined with the in-plane electric fields that arise due to the trap geometry, constrains the maximal density and lifetime of trapped excitons. We derive an analytic estimate of these values and determine their dependence on the trap geometry, thus suggesting the optimal design for high density trapping as a route for observing excitonic Bose-Einstein condensation. © 2005 The American Physical Society.

Abstract:

The method of Jain and Kamilla [J. K. Jain and R. K. Kamilla, Phys. Rev. B 55, R4895 (1997)] allows numerical generation of composite-fermion trial wave functions for large numbers of electrons in high magnetic fields at filling fractions of the form ν=p (2mp+1) with m and p positive integers. In the current paper we generalize this method to the case where the composite fermions are in an effective (mean) field with opposite sign from the actual physical field, i.e., when p is negative. We examine both the ground-state energies and the low-energy neutral excitation spectra of these states. Using particle-hole symmetry we can confirm the correctness of our method by comparing results for the series m=1 with p>0 (previously calculated by others) to our results for the conjugate series m=1 with p<0. Finally, we present similar results for ground-state energies and low-energy neutral excitations for the states with m=2 and p<0, which were not previously addressable, comparing our results to the m=1 case and the p>0, m=2 cases. © 2005 The American Physical Society.

Abstract:

We have studied the effect of optically-induced random, anisotropic disorder on the magnetoresistance of a two-dimensional electron gas by exposing the sample to an anisotropic laser speckle pattern. Changes in the amplitude of the Shubnikov-de Haas oscillations can be explained in terms of easy and hard conductivity paths, parallel and perpendicular to the long axis of the oval speckle grains, respectively. © 2005 American Institute of Physics.