Abstract: 

 We present a theoretical approach that allows understanding the quantum light spectroscopy and interpretation of experimental data from first principles and discuss the main theoretical physics concepts and tools that stand behind it. The latter include (i) Hamiltonian vs Lagrangian picture in classical and quantum mechanics, (ii) Second quantization, (iii) Feynman path integral, (iv) Reduced description and effective action, and (v) Gauge invariance and generalized effective action. The theoretical approach is based on (i) quantum dynamics in Liouville space of mixed states, (ii) Computing the optical signals directly using the many-body Green function techniques, and (iii) Describing the classical light sources/lasers via classical external polarization, rather than a classical driving field produced by the lasers.

 

 Quantum light nonlinear spectroscopic techniques are attributed to the Liouville space Feynman diagrams that label perturbative contributions to the signals, associated with different dynamical processes in a system under spectroscopic study. Due to optical nonlinearity in an auxiliary system, e.g., in a parametric down conversion (PDC) crystal light, produced by a laser shows quantum properties, despite containing a macroscopic number of photons. Quantum features of light, appearing in such spectroscopies, are attributed to loops in Feynman diagrams that describe the corresponding signals. Applications are made to nonlinear response of photosynthetic excitons and difference-frequency-generation spectroscopy.

 

Contact.  안드레이모스칼렌코 교수 (moskalenko@kaist.ac.kr)