Quantum optical models of high-order harmonic generation in two-level system

B. K. Mohanty

Daniel F. Walls, C. T. Tindle

Péter Földi, István Magashegyi, Ákos Gombkötő +1 more

Optical generation of high-order harmonics is a prototypical example of nonlinear light–matter interactions in the high-field regime. Quantum optical effects have recently been demonstrated to have a significant influence on this phenomenon. These findings underline the importance of understanding the dynamics of the quantized electromagnetic field during high-order harmonic generation. In the following, we discuss the challenges that are related to the theoretical description of this process and summarize the results that were obtained using the high-field, multimode generalization of well-known quantum optical models that are based on the concept of the two-level atom.

Ákos Gombkötő, Péter Földi, Sándor Varró

We present a study of photon statistics associated with high-order harmonic generation (HHG) involving one-mode and intermodal correlations of the high harmonic photons. The aim of the paper is to give insight into the nonclassical properties of high-order harmonic modes. To this end, we use a simplified model describing an elementary quantum emitter: the model of a two-level atom. While the material system is extremely simplified in this description, the conclusions and the methods may be generalized for more complex cases. Our primary interest is an effective model of HHG in which the exciting pulse is classical and the harmonics are quantized, although we touch upon the more generalized, fully quantized model as well. Evolution of the Mandel parameter, photon antibunching, squeezing, and cross correlations are calculated. Results imply that with respect to a single quantized emitter, nonclassicality of the harmonics is present: sub-Poissonian photon statistic and squeezing can characterize certain optical modes, while strong anticorrelation can also be present.

Marcelo F. Ciappina

Luis Plaja, L. Roso

Coherent high-order harmonic generation by an isolated two-level system is studied. A perturbative theory, for the adiabatic regime, is presented that describes the plateau structure experimentally found in noble gases. Numerical results, out of the rotating wave approximation, are used to check the analytical predictions. A dressed atom picture is introduced that shows the role of multiphoton resonances, tuned due to the light shift, to enhance high-order harmonic generation.