My research topic is related to EIT, cold atoms and slow light in resonant media.
Electromagnetically Induced Transparency
Electromagnetically induced transparency (EIT) is a quantum interference phenomenon arising from the coupling of coherent optical fields to the quantum states of the atomic system. If the alternative transition pathways exist between the relevant quantum states, the total probability of a transition is the squared sum of the individual probability amplitudes. It causes the interference between quantum transitions leading to either an enhancement (constructive interference) or a cancellation (destructive interference) in the total transition probability. As a consequence, quantum interference may lead to significant modification of the optical and nonlinear properties of the material.
The concept of laser-dressed states is an alternative picture to the quantum interference. These states are described as the eigenstates of a quantum system which interacts strongly with the radiation field. The dressed states are coherent superpositions of the bare states, which are the eigenstates of the quantum system without external interaction. Coherent superpositions have well-defined amplitudes and phases relations between the atomic states in the superposition. Preparation of large number of atoms in such coherent superpositions (uniformly phased atoms) is an important features in EIT. Coherently driven media may possess rather unusual optical properties compared to incoherently driven systems. The magnitudes of linear and nonlinear susceptibilities may become comparable leading to a very high efficiency of nonlinear optical processes.
Considerable research effort devoted to EIT has been motivated by a number of remarkable applications. These include extremely efficient nonlinear optics, storage of light pulses for quantum information, lossless propagation of laser beams and population transfer inside the atomic systems. One of the significant example of EIT is the cancellation of absorption in a multilevel atomic system coherently driven by both weak and strong laser fields. In such a case EIT renders the medium completely transparent for the weak laser field. Coherence and interference effects may permit novel possibilities to build short wavelength lasers without population inversion in the laser medium. EIT driven atomic coherences can be exploited for efficient frequency conversion and the generation of ultrashort laser pulses.