Nano and Quantum Optics

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Figure 1: Light focused on the nanoscale can interact with quantum emitters, including complex molecules From, Angew. Chem. Int. Ed. 58, 8698 (2019).

The related areas of Nano and Quantum Optics are dedicated to the study of light-matter interactions at the nanoscale and at a quantum level and are two promising lines for the development of efficient, energy-saving, and compact platforms for future information technology. Nanophotonic systems offer a key advantage over other platforms: Their unique ability to concentrate light in the nanoscale (Figure 1) enables scalability and integration in the solid-state, and at the same time gives access to the quantum properties of photons. IFIMAC hosts a group of internationally recognised researchers working in this field and counts with extensive laser lab facilities for spatial, spectral, and angular characterization of nano and quantum optical effects.

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Figure 2: Nanophotonic structures allow to confine light on the nanoscale From ACS Photonics, 5(9), 3447-3451 (2018).

Nano Optics is devoted to the study of electromagnetic field propagation, confinement, and interaction with matter at a sub-wavelength scale. Advances in fabrication and characterization techniques nowadays permit the study of optical phenomena at the nanoscale. Researchers at IFIMAC have made seminal contributions to the field through the study of nano-plasmonic systems, including the phenomenon of extraordinary optical transmission through subwavelength apertures or the proposal of spoof surface plasmon polaritons that mimic the light confinement properties of metals but at lower frequencies. Other important contributions were in the field of plasmon-assisted transport in atomic- scale junctions and the propagation of electromagnetic waves in magneto-plasmonic nanostructures (Figure 2). Light-matter interaction in two-dimensional systems, such as graphene and graphene-based heterostructures, graphene relatives, transition metal dichalcogenides and their combination in vertical stacks are also investigated at IFIMAC.

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Figure 3: Ultrastrong coupling enables the spontaneous Raman scattering of incident radiation. From Phys. Rev. Lett. 129, 273602 (2022).

Quantum Optics is a related field of research, merging the areas of quantum field theory and optics, and dealing with phenomena involving light and its interaction with matter at the quantum level. The field has evolved considerably from its early studies of coherence properties of radiation and parametric processes of light to recent topics of investigation such as quantum information, manipulation of single atoms, Bose-Einstein condensation, etc. Theorists at IFIMAC have produced seminal contributions to the understanding of light emission and absorption spectra in low-dimensional semiconductor structures. We have worked on the quantum optics produced by interacting bosonic complexes describing cavity polaritons and contributed with pioneering works on the superfluidity and coherence properties of polariton gases both under resonant and non-resonant pumping (Figure 3).

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Figure 4: Energy transfer between molecules is modified by the presence of vacuum fields in a photonic cavity. From, Science 373, eabd0336 (2021).
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Figure 5: With polaritonic chemistry, chemical structure can be manipulated through strong coupling between light and matter. From ACS Photonics 9, 1096 (2022).

IFIMAC gathers leading theorists worldwide on quantum nanophotonics, the area of overlap between nano and quantum optics. The group has extensive experience on designing nanophotonic systems to achieve and control interactions between quantum emitters and photon modes and to generate quantum states of light, with a particular focus on hybrid plasmonic-photonic structures that combine the advantages of strong field confinement and long lifetimes. The group has also been at the forefront of a new interdisciplinary area of research aimed at taking advantage of QED phenomena such as strong light-matter coupling to manipulate atomic, molecular, and condensed-matter systems, and has participated actively in the birth and development of this new area of research through several seminal contributions (Figures 4 and 5).

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Figure 6: Sketch of a room temperature single photon source for quantum communication proto- cols. A quantum emitter (such as a defect in hBN) couples to the open cavity, enhancing the single photon emission.

Experimental groups at IFIMAC have a long experience on optical spectroscopy of semiconductor low-dimensional systems, such as quantum optics based on semiconductor quantum dots.

IFIMAC researchers have expertise in photon correlation techniques, properties of single photon emitters (Figure 6), time-resolved spectroscopy, quantum microcavities based on semiconductor nanostructures, exciton polaritons, and on the preparation of Bose-Einstein condensates in solid-state systems.

Furthermore, we have also developed compact laser sources based on plasmonic nanoparticles. Another very active area of experimental research at IFIMAC is the study of exciton diffusion in complex semiconductors or perovskites to optimise their ability to harvest solar energy, in combination with artificial intelligence approaches (Figure 7).

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Figure 7: Excitons in a two-dimensional perovskite are schematically represented in a. Excitons are imaged as shown in b and produce a time and position dependent fluorescence. From ACS Energy Lett. 7, 358 (2022).