General features of coherence effects in spectroscopy

C. Y. Ye, Alexander S. Zibrov, Yuri V. Rostovtsev

Spectroscopy of the Doppler broadened Rb atomic vapour coherently driven by two coupling fields is presented. Double dark resonances have been observed in different geometries of the coupling fields. A simple four-level model explains the basic counter-intuitive features of experimental spectra. The eigenvalues of the atom-field system distinguishing between the various geometries clarify the physics.

Alfred Kastler

Veniamin P. Chebotayev

Yuan Wan, N. P. Armitage

We show that the new technique of terahertz 2D coherent spectroscopy is capable of giving qualitatively new information about fractionalized spin systems. For the prototypical example of the transverse field Ising chain, we demonstrate theoretically that, despite the broad continuum of excitations in linear response, the 2D spectrum contains sharp features that are a coherent signature of a "spinon echo," which gives previously inaccessible information such as the lifetime of the two-spinon excited state. The effects of disorder and finite lifetime, which are practically indistinguishable in the linear optical or neutron response, manifest in dramatically different fashion in the 2D spectra. Our results may be directly applicable to model quasi-1D transverse field Ising chain systems such as CoNb_{2}O_{6}, but the concept can be applied to fractionalized spin systems in general.

M. Joffre, Claude Benoit à la Guillaume, Nasser N. Peyghambarian +5 more

Femtosecond measurements of coherent effects arising from exciton bleaching in bulk GaAs are reported. This phenomenon, which is characterized by spectral oscillatory structures, is general and appears whenever the temporal resolution is shorter than the material coherence time. This is shown to be a manifestation of the uncertainty relation in time-resolved spectroscopy.

G.H.C. New