Berlin 2001 – wissenschaftliches Programm

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Q: Quantenoptik

Q 28: Quantum Effects III

Q 28.3: Vortrag

Donnerstag, 5. April 2001, 18:00–18:15, H 3010

Negative Phase Time for Scattering at Quantum Wells — A Microwave Analogy Experiment — •Ralf-Michael Vetter, Astrid Haibel, and G"unter Nimtz — Universit"at zu K"oln, II. Physikalisches Institut, Z"ulpicher Str. 77, D-50937 K"oln

If a quantum mechanical particle is scattered by a potential well, the wave function of the particle can propagate with negative phase time. Negative phase times lead to propagation with negative group velocities, which means that it appears as if parts of a pulse are leaving the well before they enter.

Recently this effect was demonstrated for stimulated emission [Wang et al, Nature 7/2000], using the fact that the group velocity in the frequency regime between two closely spaced gain lines becomes −c/310.

A potential well, in contrast, shows negative phase times in the frequency region between the highest bound state inside and the first resonance above the well. Due to the analogy of the Schr"odinger and the Helmholtz equations this phenomenon is expected to be observable for electromagnetic wave propagation. Experimental data of electromagnetic wells realized by waveguides filled with different dielectrics confirm this conjecture now.