Various quantum effects have been observed in the thermodynamic of small systems. We had investigated the possible role of quantum coherence and interference on steady state and transient behavior of the quantum heat engines (QHE), e.g lasers, photovoltaic cells and photosynthetic reaction centers. We recently applied a similar concept to nanoplasmonic devices. We showed that the maximum power of a QHE that converts incoherent thermal energy into coherent cavity photons could be enhanced by manipulating quantum coherences. We further demonstrated the how the quantum coherence affects the efficiency at maximum power characteristics in generic quantum heat engines. We further investigate other quantum effects in system-bath, bath, work and measurement elements of the Quantum Heat Engines. Another area of interest is to investigate quantum statistical properties of the output of the Quantum Heat Engines based on fluctuation-dissipation relations and relevant thermodynamics. It opens an excellent opportunity to make a valuable contribution by developing new models for the transport processes and designing the new light sources with enhanced performance.
2. Quantum Meta-photonics
Beside the important and highly publicized development in quantum optics, recent experiments reported over the last couple of decades in the field of photonics have challenged our traditional understanding of light propagation, achieving new and intriguing effects such as invisibility cloaks, negative and anomalous refraction effects. The success of these new techniques to arbitrarily control light propagation are linked to the development of nanotechnology. We aim to investigate microscopically the QED models of metasurfaces that allow to achieve the optimum degree of control of all parameters of the light: momentum, polarization, angular momentum, wavelength and light statistics.
II. QUANTUM AND ULTRAFAST SPECTROSCOPY
1. Nonlinear Spectroscopy and Imaging with Quantum Light
Nonlinear optical signals are commonly calculated using a semiclassical approach that assumes a quantum system interacting with classical fields. This powerful approach is routinely used for the design and interpretation of multidimensional signals in molecules and semiconductor nanostructures. Quantum states of light provide an important tool for quantum information processing, secure communication, lithography. Classical light is fundamentally limited by the frequency-time uncertainty, whereas quantum light, e.g. entangled photons have independent temporal and spectral characteristics not subjected to this uncertainty. In addition low intensity requirements for multi-photon processes make them ideally suited for minimizing damage in imaging applications. Recently we developed techniques that make use of the quantum nature of the field in spectroscopic and imaging applications and allow to distinguish quantum pathways of matter. Modern quantum technologies use quantum fields but typically employ very simple models of matter (q bits). We developed a dagrammatic approach which can handle complex fields interacting with complex molecules. Unlike the semiclassical formalism that treats the signal mode macroscopically using Maxwell's equations, our approach allows for a fully microscopic calculation of the entire process. The availability of entangled photon sources and ultrafast optical setups suggest that the spectroscopy and imaging with quantum light is an emerging field in physics, where theoretician can make a distinct contribution by predicting and simulating novel experiments.
2. Ultrafast Raman Spectroscopy
The excited state dynamics of molecules plays a key role in many photophysical processes and has attracted considerable experimental and theoretical attention. Real time structural information about rearrangement of atoms in complex reactions can be inferred directly from time resolved vibrational spectroscopy. Typically an ultrashort laser pulse in the visible or the UV excites the molecule to a bright valence excited state, launching a photoreaction or non-adiabatic relaxation process. The vibrational dynamics can then be probed by a spontaneous or stimulated Raman process. We discovered microscopic origin for the temporal and spectral resolution and developed the optimization strategies for several prominent homodyne- and heterodyne-detected, time- and frequency-domain Raman techniques. We implemented the three simulation protocols that vary in complexity of the multi-mode nuclear dynamics and form a hierarchy of approximations. These simulation protocols can be further extended for studies of the charge motion with applications ranging from natural and artificial light harvesting to electron transfer in proteins and novel materials. Experiments, which employ sequences of attosecond X-ray pulses provide novel windows into molecular valence electronic structure and dynamics with much higher resolution than visible light. We investigated the microscopic origin of the nonlinear light scattering (NLS) caused by the time-evolving superposition of electronic excitations. Furthermore using quantum electrodynamic framework, we identified new information that can be measured by X-ray diffraction signals from a single amino acid molecule (cysteine). We demonstrated the possibility to coherently control electron transfer in molecules by attosecond Raman pulse sequence. We further developed a novel spectroscopic technique for background free tracking of electron coherences for conical intersection detection. Our theory and simulations can guide future experimental studies on the structures of nano-particles and proteins.
3. Nonlinear X-ray Spectroscopy with High Harmonics
Ultrafast pump-high-harmonic-generation-probe spectroscopy aims to provide a unique observation window into electronic dynamics while using the infrared or visible light sources. While it is widely accepted that the role of excited bound states in high harmonic generation is negligible, its dynamics becomes significant in time-resolved pump-probe measurements. Various contributions due to quantum interference in electron ionization and recombination with atomic system along with multiple dephasing processes are responsible for the new information that can be probed. Semi-perturbative theory based on the density matrix Liouville space formalism supported by experimental demonstration allows simplified yet physically transparent interpretation and prediction of a new effects in electron dynamics.