The recent progress in nanotechnology [1, 2] and single-molecule spectroscopy [3][4][5] paves the way for cost-effective organic quantum optical technologies emergent with a promise to useful devices operating at ambient conditions. We harness a π-conjugated ladder-type polymer strongly coupled to a microcavity forming hybrid light-matter states, so-called exciton-polaritons, to create excitonpolariton condensates with quantum fluid properties. Obeying Bose statistics, exciton-polaritons exhibit an extreme nonlinearity undergoing bosonic stimulation [6] which we have managed to trigger at the single-photon level, thereby providing an efficient way for all-optical ultra-fast control over the macroscopic condensate wavefunction. Here, we utilise stable excitons dressed with high energy molecular vibrations allowing for single-photon nonlinearity operation at ambient conditions. This opens new horizons for practical implementations like sub-picosecond switching, amplification and all-optical logic at the fundamental quantum limit.

We propose a method for increasing the Raman scattering from an ensemble of molecules by up to four orders of magnitude. Our method requires an additional coherent source of IR radiation with the half-frequency of the Stokes shift. This radiation excites the molecule electronic subsystem that in turn, via Fröhlich coupling, parametrically excites nuclear oscillations at a resonant frequency. This motion is coherent and leads to a boost of the Raman signal in comparison to the spontaneous signal because its intensity is proportional to the squared number of molecules in the illuminated volume.There are several effective methods for enhancing Raman signals. Surface-enhanced Raman scattering (SERS) [20][21][22] and tip-enhanced Raman spectroscopy (TERS) [9,23,24] utilize the enhancement of the local field around a molecule using the plasmon resonance [25][26][27]. Other methods employ the parametric excitation of nucleus vibrations in the molecule. This approach is used in coherent anti-Stokes Raman scattering (CARS) [28][29][30], in coherent Stokes Raman scattering (CSRS) [31][32][33][34] as well as in surface-enhanced coherent anti-Stokes Raman scattering (SECARS) [35]. Obtaining an enhancement in CARS requires strong driving fields. Consequently, some undesirable side effects arise; in particular, the stimulated Raman scattering

We develop a quantum theory of atomic Rayleigh scattering. Scattering is considered as a relaxation of incident photons from a selected mode of free space to the reservoir of the other free space modes. Additional excitations of the reservoir states which appear are treated as scattered light. We show that an entangled state of the excited atom and the incident photon is formed during the scattering. Due to entanglement, a photon is never completely absorbed by the atom. We show that even if the selected mode frequency is incommensurable with any atomic transition frequency, the scattered light spectrum has a maximum at the frequency of the selected mode. The linewidth of scattered light is much smaller than that of the spontaneous emission of a single atom, therefore, the process can be considered as elastic. The developed theory does not use the phenomenological concept of "virtual level.