Search

Graphene flakes acting as photonic nanoantennas may sustain strong electromagnetic field localization and enhancement. To exploit the field enhancement, quantum emitters such as atoms or molecules should be positioned in such close proximity to the flake that electron tunneling might influence the optical and electronic properties of the system. However, tunneling is usually not considered if the optical coupling mechanism between quantum emitters and nanoantennas is at focus. This work presents a framework for describing the electron dynamics in hybrid systems consisting of graphene nanoflakes coupled both electronically and optically to adatoms and subject to external illumination. Our framework combines the single-particle tight-binding approach with a nonlinear master equation formalism that captures both optical and electronic interactions. We apply the framework to demonstrate the impact of electron tunneling between the adatom and the flake on emblematic quantum optical phenomena: degradation of coherent Rabi oscillations and quenching of Purcell spontaneous emission enhancement in two-level adatoms in proximity of triangular graphene nanoflakes., M.K. acknowledges support from the National Science Centre, Poland (Project No. 2016/23/G/ST3/04045). M.P. and K.S. acknowledge support from the National Science Centre, Poland (Project No. 2020/39/I/ST3/00526). M.M.M. acknowledges financial support through the Research Travel Grant by the Karlsruhe House of Young Scientists (KHYS). M.M.M. and C.R. acknowledge support by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) (Project No. 378579271) within Project RO 3640/8-1 and from the VolkswagenStiftung. A.A. acknowledges the Spanish Ministry of Science and Innovation with PID2019-105488GB-I00 and PCI2019-103657, the Basque Government through the University of the Basque Country Project No. IT-1246-19, the European Commission from the NRG-STORAGE Project (No. GA 870114) and H2020-FET OPEN Project MIRACLE (No. GA 964450). A.A. carried this study under the Translacional CommonLaboratory (LTC-Green Concrete).

We discuss how spatial asymmetry of quantum systems quantified in terms of permanent dipole moments influences their emission properties in different light-matter interaction regimes. Applications for spontaneous emission suppression and coherent emis-sion are explored.

Adsorbed atoms (adatoms) coupled to the matrix of solid state host materials as impurities can significantly modify their properties. Especially in low-dimensional materials, such as one-dimensional organic polymer chains or quasi-one-dimensional graphene nanoribbons, intriguing manipulation of the optical properties, such as the absorption cross section, is possible. The most widely used approach to couple quantum emitters to optical antennas is based on the Purcell effect. This formalism, however, does not comprise charge transfer from the emitter to the antenna, but only spontaneous emission of the quantum emitter into the tailored photonic environment, that is evoked by the antenna. To capture such effects, we present a tight-binding formalism to couple an adatom to a finite Su-Schrieffer-Heeger chain, where the former is treated as a two-level system and the latter acts as an optical antenna. We systematically analyze how the coupling strength and the position of the adatom influence the optical properties of the molecular chains in the model. We take into account charge transfer from the adatom to the chain and vice versa via an intersystem hopping parameter, and also include Coulomb interaction within the chain as well as between the adatom and the chain. We show that coupling the adatom to one of the bulk atoms of the linear chain results in a substantial change in optical properties already for comparatively small coupling strengths. We also find that the position of the adatom crucially determines if and how the optical properties of the chains are altered. Therefore, we identify this adatom-chain hybrid system as a tunable platform for light-matter interaction at the nanoscale., M.M.M. acknowledges financial support through the Research Travel Grant by the Karlsruhe House of Young Scientists (KHYS). M.M.M. and C.R. acknowledge support by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) (Project No. 378579271) within Project RO 3640/8-1 and from the VolkswagenStiftung. M.K. and K.S. acknowledge the support from the National Science Centre, Poland (Project No. 2016/23/G/ST3/04045). A.A. acknowledges support from the Spanish Ministry of Science and Innovation with Grants No. PID2019-105488GB-I00 and No. PCI2019-103657, the Basque Government through the University of the Basque Country Project No. IT-1246-19, and the European Commission from the NRG-STORAGE Project (No. GA 870114) and H2020-FET OPEN Project MIRACLE (No. GA 964450).

The Rabi Hamiltonian, describing the interaction between a two-level atomic system and a single cavity mode of the electromagnetic field, is one of the fundamental models in quantum optics. The model becomes exactly solvable by considering an atom without permanent dipole moments, whose excitation energy is quasi-resonant with the cavity photon energy, and by neglecting the non resonant (counter-rotating) terms. In this case, after including the decay of either the atom or the cavity mode to a continuum, one is able to derive the well-known phenomenology of quasi-resonant transitions, including the fluorescence triplets. In this work we consider the most general Rabi model, incorporating the effects of permanent atomic electric dipole moments, and, based on a perturbative analysis, we compare the intensities of emission lines induced by rotating terms, counter-rotating terms and parity-symmetry-breaking terms. The analysis reveals that the emission strength related to the existence of permanent dipoles may surpass the one due to the counter-rotating interaction terms, but is usually much weaker than the emission due to the main, resonant coupling. This ratio can be modified in systems with a reduced dimensionality or by engineering the energy spectral density of the continuum., 11 pages, 7 figures

If a two-level atomic system characterized by inversion symmetry in space is coupled to a classical electromagnetic field, it undergoes Rabi oscillations where the population flips between the ground and excited levels. We investigate a scenario, where a system of broken inversion symmetry is used instead. In such case the dynamics is modified for the following reason: Eigenstates of an asymmetric system can be characterized with a permanent electric dipole moment originating from the polarization of charges, which plays a significant role of an additional source of dipole radiation. Its frequency corresponds to the Rabi frequency of population transfer between the eigenstates and therefore is optically tunable with the intensity of the driving field. We construct the numerical solver to simulate the medium of such asymmetric systems driven by the laser beam and by the Bloch-Maxwell equations calculate the generated radiation's propagation.

The photonic environment can significantly influence emission properties and interactions among atomic systems. In such scenarios, frequently the electric dipole approximation is assumed that is justified as long as the spatial extent of the atomic system is negligible compared to the spatial variations of the field. While this holds true for many canonical systems, it ceases to be applicable for more contemporary nanophotonic structures. To go beyond the electric dipole approximation, we propose and develop in this article an analytical framework to describe the impact of the photonic environment on emission and interaction properties of atomic systems beyond the electric dipole approximation. Particularly, we retain explicitly magnetic dipolar and electric quadrupolar contributions to the light-matter interactions. We exploit a field quantization scheme based on electromagnetic Green's tensors, suited for dispersive materials. We obtain expressions for spontaneous emission rate, Lamb shift, multipole-multipole shift and superradiance rate, all being modified with dispersive environment. The considered influence could be substantial for suitably tailored nanostructured photonic environments, as demonstrated exemplarily., Comment: 2 figures + supplementary material, 21 pages altogether

A metasurface in the metal-insulator-grating configuration is designed and optimised to support enhancement of coherent Raman signal of selected molecules orders of magnitude above the single-molecule detection threshold. The tunability is demonstrated by adjusting the structure to match selected Raman peaks of rhodamine, however, its spectral response is broad enough to cover a range of Raman shifts. Finally, the grating allows switching between distinct values of Raman shift with a single metasurface illuminated at different angles.

In this paper, we study the collective effects which appear as a pair of quantum emitters is positioned in close vicinity to a plasmonic nanoparticle. These effects include multipole&ndash, multipole interaction and collective decay, the strengths and rates of which are modified by the presence of the nanoparticle. As a result, entanglement is generated between the quantum emitters, which survives in the stationary state. To evaluate these effects, we exploit the Green&rsquo, s tensor-based quantization scheme in the Markovian limit, taking into account the corrections from light&ndash, matter coupling channels higher than the electric dipole. We find these higher-order channels to significantly influence the collective rates and degree of entanglement, and in particular, to qualitatively influence their spatial profiles. Our findings indicate that, apart from quantitatively modifying the results, the higher-order interaction channels may introduce asymmetry into the spatial distribution of the collective response.

Resonances sustained by plasmonic nanoparticles provide extreme electric field confinement and enhancement into the deep subwavelength domain for a plethora of applications. Recent progress in nanofabrication made it even possible to tailor the properties of nanoparticles consisting of only a few hundred atoms. These nanoparticles support both single-particle-like resonances and collective plasmonic charge density oscillations. Prototypical systems sustaining both features are graphene nanoantennas. In pushing the frontier of nanoscience, traditional identification, and classification of such resonances is at stake again. We show that in such nanostructures, the concerted electron cloud oscillation in real space does not necessarily come along with collective dynamics of conduction band electrons in energy space. This unveils an urgent need for a discussion of how a plasmon in nanostructures should be defined. Here, we propose to define it relying on energy space dynamics. The unambiguous identification of the plasmonic nature of a resonance is crucial to find out whether desirable plasmon-assisted features, such as frequency conversion processes, can be expected from a resonance. We elaborate an energy-based figure of merit that classifies the nature of resonances in nanostructures, motivated by tight binding simulations with a toy model consisting of a linear chain of atoms. We apply afterward the proposed figure of merit to a doped hexagonal graphene nanoantenna, which is known to support plasmons in the near infrared and single-particle-like transitions in the visible., M.M.M. acknowledges financial support through the Research Travel Grant by the Karlsruhe House of Young Scientists (KHYS). M.M.M. and C.R. acknowledge support by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation)—project number 378579271—within project RO 3640/8-1 and from the VolkswagenStiftung. M.M.M. is grateful for the support of the Toruń Astrophysics/Physics Summer Program TAPS 2019 and the PROM project no. PPI/PRO/2018/1/00016/U/001 by the Polish National Agency for Academic Exchange. M.M.M., M.K., and K.S. acknowledge the hospitality of the Donostia International Physics Center. M.K. acknowledges the financial support from the Foundation for Polish Science (FNP) (project First Team/2017-3/20 cofinanced by the European Union under the European Regional Development Fund). M.P. and A.A. acknowledge financial support by project PID2019-105488GB-I00 of the Spanish Ministry of Science and Innovation, and the Gobierno Vasco—UPV/EHU project IT1246-19. K.S. acknowledges support from the National Science Centre, Poland (project no. 2016/23/G/ST3/0404).

In the pioneering work of Purcell [1], the possibility to control spontaneous emission lifetimes of quantum emitters by tailoring their electromagnetic surroundings was widely investigated and verified in various types of cavities or band-gap environments. This includes semiconductor microstructures, photonic crystals, and plasmonic nanoparticles. Due to the extraordinary ability of plasmonic nanostructures to confine light into subwavelength spatial domains, steps beyond the paradigmatic electric dipole approximation in the theoretical description of this process may be necessary [2].

Photons produced in the SPDC process typically propagate through optical elements such as waveguides, lenses and beam splitters. We aim to exploit unconventional optical elements, whose fabrication has recently become possible due to the rapid development of nanotechnologies. Such miniaturized devices are typically integrated on microchips that may later become parts of larger quantum circuits. An example is provided by metamaterials, which are periodic arrays of metallic nanoparticles. These nanoparticles support surface plasmon polaritons - hybrid excitations that combine electromagnetic fields with coherent oscillations of valence-electron plasma. Here we experimentally characterize in free space a nanostructural beam splitter, which was designed to feature 25 % of reflection and transmission, and 50 % of absorption. Furthermore we experimentally show quantum interference in that device.

Photonic quantum technologies allow quantum phenomena to be exploited in applications such as quantum cryptography, quantum simulation and quantum computation. A key requirement for practical devices is the scalable integration of single-photon sources, detectors and linear optical elements on a common platform. Nanophotonic circuits enable the realization of complex linear optical systems, while non-classical light can be measured with waveguide-integrated detectors. However, reproducible single-photon sources with high brightness and compatibility with photonic devices remain elusive for fully integrated systems. Here, we report the observation of antibunching in the light emitted from an electrically driven carbon nanotube embedded within a photonic quantum circuit. Non-classical light generated on chip is recorded under cryogenic conditions with waveguide-integrated superconducting single-photon detectors, without requiring optical filtering. Because exclusively scalable fabrication and deposition methods are used, our results establish carbon nanotubes as promising nanoscale single-photon emitters for hybrid quantum photonic devices. Single photons are generated from electrically driven semiconducting single-walled carbon nanotubes embedded in a photonic circuit. Pronounced antibunching is observed when photon correlation is measured at cryogenic temperatures.

This work is a proposition of an experimental platform to observe quantum fictitious anticentrifugal force. We present an analytical and numerical treatment of a rectangular toroidal dielectric waveguide. Solving the Helmholtz equation, we obtain analytical solutions for transverse spatial modes and estimate their number as a function of system characteristics. On top of that, the analysis of the structure is extended onto a real material platform, a thin-film lithium niobate on insulator rib waveguide. The framework presented here can be applied directly to analyze the phenomenon of quantum anticentrifugal force.

Plasmonic nanoantennas sustain an extraordinary ability to concentrate light in subwavelength spatial domains. This confinement is accompanied with a corresponding enhancement. Hence, unprecedented light-matter coupling strength can achieved to quantum emitters positioned near the focal point. Thus, utilization of nanoantennas holds promise for rapid addressing of chip-integrated quantum emitters with light, or for a significant boost of performance of such quantum emitters as nonclassical light sources. Moreover, nanoantennas can be exploited to engineer the emission characteristics, or even quantum properties of light, such as statistics or degree of entanglement. To discuss these applications, we have developed a framework that treats nanoantennas as open cavities of arbitrary spectra, coupled to quantum emitters characterized by a configuration of discrete energy levels. In this way, we drop the usual, but often unrealistic assumption of a single-Lorentzian nanoantenna spectrum. In this contribution we introduce the method and apply it to several example designs tailored for specific functionalities.

We derive the quantum mechanical description of light-matter interactions in optical cavities characterized solely by radiative decay. Unique to radiative decay is the conservation of photon number and coherence, in stark contrast to absorptive losses. This prohibits the description of such cavities by traditional means, e.g., coupling it to a bath of harmonic oscillators into which energy is dissipated. Here, we propose a description of cavities with radiative decay by introducing cavity and noise operators in terms of scattering modes. A multimode input-output formalism to predict measurable far field quantities arises naturally. We apply our general model to the special case of the single excitation regime. We find dynamics reminiscent of the dissipative Jaynes-Cummings model, but with vanishing backaction and a rich temporal and spectral structure of the output modes.

We analyze the potential of nanoantennas to enhance and control emission of entangled photon pairs from epitaxially grown quantum dot s (InAs/InP). Suitably designed combination of metallic and dielectric components leads to improved emission directivity at a considerable level of fidelity of emitted states with respect to the target perfectly entangled states.

Plasmonic and dielectric nanoparticles provide a platform to realize efficient coupling of light and matter at nanoscale, capitalizing on interaction channels hardly accessible in free space. In this work we investigate parallel electric and magnetic interaction channels that may drive the same transition of chiral molecules, intensified with nanoparticles whose optical response is dominated by a magnetic resonance, enhancing the effect of circular dichroism.

Unitary transformations are routinely modeled and implemented in the field of quantum optics. In contrast, nonunitary transformations that can involve loss and gain require a different approach. In this theory work, we present a universal method to deal with nonunitary networks. An input to the method is an arbitrary linear transformation matrix of optical modes that does not need to adhere to bosonic commutation relations. The method constructs a transformation that includes the network of interest and accounts for full quantum optical effects related to loss and gain. Furthermore, through a decomposition in terms of simple building blocks it provides a step-by-step implementation recipe, in a manner similar to the decomposition by Reck et al. [Reck et al., Phys. Rev. Lett. 73, 58 (1994)] but applicable to nonunitary transformations. Applications of the method include the implementation of positive-operator-valued measures and the design of probabilistic optical quantum information protocols., We also provide a MATLAB code for numerically implementing the full decomposition on GitHub, at https://github.com/NoraTischler/QuantOpt-linear-transformation-decomposition

Recently, the needs to achieve a very high traffic capacity and superfast quantum computing led to advancement in optical waveguide technology. The selection of material with a high refractive index and transparent within the telecommunication wavelength range are crucially needed to achieve these. In this paper, the performance of two promising quantum materials, Silicon on Insulator (SOI) and Lithium Niobate on Insulator (LNOI) rib waveguide were studied. The mode analysis was conducted by using a finite element method to observe the confinement electromagnetic wave across rib waveguide. Apart from the variation of a material index, the width and height of core were optimized to achieve single mode propagation at the wavelength of 1550 nm. Based on the simulation work, it is shown that both material structures were able to produce single mode propagation with SOI showing higher confinement compared to the LNOI rib waveguide structure. LNOI structure was able to provide wide range of propagation signal wavelength.

We analytically examine propagation of surface plasmon polaritons (SPPs) at a thin metallic film between glass substrate and electromagnetically-induced-transparency (EIT) medium. High-precision and high-resolution in frequency domain provided by EIT paves the way towards plasmonic group velocities reduction even by $4$ orders of magnitude and corresponding lifetime enhancement of SPPs up to microseconds., Comment: 5 pages, 5 figures

Converting signals between different electromagnetic modes is an asset for future information technologies. In general, slightly asymmetric optical nanoantennas enable the coupling between bright and dark modes sustained by an optical nanoantenna. However, the conversion efficiency might be very low. Here, we show that the additional incorporation of a quantum emitter allows to tremendously enhance this efficiency. The enhanced local density of states cycles the quantum emitter between its upper and lower level at an extremely hight rate; hence converting the energy very efficient. The process is robust with respect to possible experimental tolerances and adds a new ingredient to be exploited while studying and applying coupling phenomena in optical nanosystems., 5 pages, 3 figures

Statistical properties of outgoing light pulses are studies after they have been stored in a medium of atoms in the tripod configuration. A generalized Hong-Ou-Mandel interference, storing of squeezed states and homodyne signal analysis are discussed in the context of their dependence on the parameters of the control fields used for light storage and release., Comment: 5 figures

Highly integrated single photon sources are key components in future quantum-optical circuits. Whereas the probabilistic generation of single photons can routinely be done by now, their triggered generation is a much greater challenge. Here, we describe the triggered generation of single photons in a hybrid plasmonic device. It consists of a lambda-type quantum emitter coupled to a multimode optical nanoantenna. For moderate interaction strengths between the subsystems, the description of the quantum optical evolution can be simplified by an adiabatic elimination of the electromagnetic fields of the nanoantenna modes. This leads to an insightful analysis of the emitter's dynamics, entails the opportunity to understand the physics of the device, and to identify parameter regimes for a desired operation. Even though the approach presented in this work is general, we consider a simple exemplary design of a plasmonic nanoantenna, made of two silver nanorods, suitable for triggered generation of single photons., Comment: 13 pages, 7 figures

A novel scheme is proposed to generate a maximally entangled state between two qubits by means of a dissipation-driven process. To this end, we entangle the quantum states of qubits that are mutually coupled by a plasmonic nanoantenna. Upon enforcing a weak spectral asymmetry in the properties of the qubits, the steady-state probability to obtain a maximally entangled, subradiant state approaches unity. This occurs despite the high losses associated to the plasmonic nanoantenna that are usually considered as being detrimental. The entanglement scheme is shown to be quite robust against variations in the transition frequencies of the quantum dots and deviations in their prescribed position with respect to the nanoantenna. Our work paves the way for novel applications in the field of quantum computation in highly integrated optical circuits., 9 pages, 5 figures

An optical nanoantenna and adjacent atomic systems are strongly coupled when an excitation is repeatedly exchanged between these subsystems prior to its eventual dissipation into the environment. It remains challenging to reach the strong coupling regime but it is equally rewarding. Once being achieved, promising applications as signal processing at the nanoscale and at the single photon level would immediately come into reach. Here, we study such hybrid configuration from different perspectives. The configuration we consider consists of two identical atomic systems, described in a two-level approximation, which are strongly coupled to an optical nanoantenna. First, we investigate when this hybrid system requires a fully quantum description and provide a simple analytical criterion. Second, a design for a nanoantenna is presented that enables the strong coupling regime. Besides a vivid time evolution, the strong coupling is documented in experimentally accessible quantities, such as the extinction spectra. The latter are shown to be strongly modified if the hybrid system is weakly driven and operates in the quantum regime. We find that the extinction spectra depend sensitively on the number of atomic systems coupled to the nanoantenna., 14 pages, 7 figures

We propose to use nanoantennas coupled to incoherently pumped quantum dots for ultra-bright single photon emission. Besides fully quantum calculations, we analyze an analytical expression for the emitted photon rate. From these analytical considerations it turns out that the Purcell factor and the pumping rate are the main quantities of interest. We also disclose a trade-off between the emitted photon rate and the nonclassical nature of the emitted light. This trade-off has to be considered while designing suitable nanoantennas, which we also discuss in depth.

The cross-Kerr effect is studied for two pulses propagating in an atomic medium in a tripod configuration, dressed by a strong standing wave coupling beam. Nonlinear phase shifts for both transmitted and reflected beams are calculated taking into account the redistribution of the population among the atomic levels which allows one to study the phase shifts in a wide range of pulse detunings. The influence of other parameters, e.g., the intensity of the control field and the relaxation rates, on the cross-Kerr effect is also examined in detail., Comment: 6 figures

Cross-Kerr nonlinearities are analyzed for two light beams propagating in an atomic medium in the tripod configuration, dressed by a strong standing-wave laser field that induces periodic optical properties. The reflection and transmission spectra as well as the phases of both the reflected and transmitted components of the two beams are analyzed theoretically with nonlinearities up to third order being taken into account. Ranges of parameters are sought in which the cross-Kerr effect can be used as the basis of the phase gate.

We investigate the optical properties of a hybrid system consisting of a quantum emitter that is strongly coupled to a pair of metallic nanoparticles. Emphasis is put on the exploitation of such a hybrid system as a highly efficient source for nonclassical light. The properties of the emitted light are analyzed in detail for a system that was designed to maximize the single-photon emission rates. Such sources may represent important constituents for the future architecture of fully integrated quantum circuits and may soon drastically improve the performance of quantum information protocols.

Plasmonic nanostructures attract tremendous attention as they confine electromagnetic fields well below the diffraction limit while simultaneously sustaining extreme local field enhancements. To fully exploit these properties, the identification and classification of resonances in such nanostructures is crucial. Recently, a novel figure of merit for resonance classification has been proposed [Müller et al., J. Phys. Chem. C 124, 24331–24343 (2020)] and its applicability was demonstrated mostly to toy model systems. This novel measure, the energy-based plasmonicity index (EPI), characterizes the nature of resonances in molecular nanostructures. The EPI distinguishes between either a single-particle-like or a plasmonic nature of resonances based on the energy space coherence dynamics of the excitation. To advance the further development of this newly established measure, we present here its exemplary application to characterize the resonances of graphene nanoantennas. In particular, we focus on resonances in a doped nanoantenna. The structure is of interest, as a consideration of the electron dynamics in real space might suggest a plasmonic nature of selected resonances in the low doping limit but our analysis reveals the opposite. We find that in the undoped and moderately doped nanoantenna, the EPI classifies all emerging resonances as predominantly single-particle-like, and only after doping the structure heavily, the EPI observes plasmonic response., M.M.M. acknowledges financial support through the Research Travel Grant by the Karlsruhe House of Young Scientists (KHYS). M.M.M. and C.R. acknowledge support by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) (Project No. 378579271) within Project RO 3640/8-1 and from the VolkswagenStiftung. M.M.M. is grateful for the support of the Toruń Astrophysics/Physics Summer Program TAPS 2019 and the PROM (Project No. PPI/PRO/2018/1/00016/U/001) by the Polish National Agency for Academic Exchange. M.M.M., M.K., and K.S. acknowledge the hospitality of the Donostia International Physics Center. M.K. acknowledges financial support from the National Science Centre, Poland (Grant No. 2016/23/D/ST2/02064). M.P. and A.A. acknowledge financial support by Project No. PID2019-105488GB-I00 of the Spanish Ministry of Science and Innovation, and the Gobierno Vasco UPV/EHU (Project No. IT1246-19). K.S. acknowledges support from the National Science Centre, Poland (Project No. 2016/23/G/ST3/04045), the European Commission from the NRG-STORAGE project (GA 870114) and H2020-FET OPEN project MIRACLE (GA 964450).