Dresden 2011 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 85: Poster Session II
HL 85.99: Poster
Thursday, March 17, 2011, 18:00–21:00, P4
Analysis of squeezed LO phonon states in a QD with the help of the Wigner function — •Daniel Wigger1, Doris Reiter1, Tilmann Kuhn1, and Vollrath Martin Axt2 — 1Institut für Festkörpertheorie, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Str. 10, 48149 Münster — 2Theoretische Physik III, Universität Bayreuth, 95440 Bayreuth
We study the fluctuation properties of non-classical phonon states within the model of an optically excited semiconductor quantum dot (QD). The QD is modeled in the strong confinement limit as a two level system. An ultrashort laser pulse creates an exciton in the QD which can be manipulated by further pulses. The exciton is coupled to the longitudinal optical (LO) phonons and, thus, lattice vibrations are created by the optical manipulation of the QD. For two pulses with a certain time delay and relative phase we find that the lattice fluctuations are squeezed, i.e., the fluctuations fall below the fluctuations of the phonon vacuum. [Sauer et al. PRL 105, 157401 (2010)] The quantum mechanical characteristics of the phonon states are studied using the Wigner function which allows an instructive interpretation of the phononic system. With the Wigner function we analytically calculate the fluctuation properties of the lattice displacement and momentum caused by the LO phonons and explain the mechanisms leading to squeezing.