Kvantni svetlobni izvori v mehkih in bioloških snoveh

Over the past two decades, rapid progress in the development of quantum light sources has positioned quantum optics as a cornerstone of emerging quantum technologies. This thesis presents two entirely new and distinct advances in quantum optics, each introducing quantum light sources into unconventional environments. In the first part, nanoparticles of hexagonal boron nitride (hBN) with optically active color centers were successfully introduced into living cells, where they emitted light in the form of temporally isolated single photons. Unlike conventional light sources, each color center emits exactly one photon at a time — a fundamentally quantum mechanical phenomenon with no classical analogue. The emitters showed excellent single-photon purity, outstanding emission stability with no photobleaching or spectral drift over several hours, and negligible impact on cell health. Crucially, because different color centers emit at different wavelengths and with distinct spectral profiles, they can serve as unique optical fingerprints. Combining just a few per cell allows virtually unlimited numbers of cells to be uniquely tagged. Beyond labeling, the single-photon nature of these emitters opens a path toward quantum-limited sensing and imaging inside living tissue. In addition to single-photon emitters, we also investigated sources of entangled photon pairs. These have traditionally relied on solid-state nonlinear crystals, which are rigid, difficult to tune, and offer little flexibility once fabricated. To overcome these limitations, we turn to soft matter: we developed and investigated sources based on ferroelectric nematic liquid crystals (FNLCs), a newly discovered class of organic materials with exceptionally strong intrinsic electric polarization and optical nonlinearity, as a platform for generating entangled photon pairs through spontaneous parametric down-conversion (SPDC). The results presented here mark the first demonstration of photon-pair generation in organic matter via SPDC. By reorienting the liquid crystal molecules through sample geometry or applied electric fields, the intensity, polarization state, and degree of entanglement of the generated photon pairs can all be controlled — a level of tunability not available in conventional solid-state sources. Additionally, chiral FNLCs with a self-assembled helical structure were shown to produce photon-pair generation rates comparable to or exceeding those of the best solid-state platforms. By introducing scalable, efficient, and reconfigurable quantum light sources with functionalities beyond those of conventional solid-state platforms, this work opens new directions in quantum optics and related technologies.