This PDF file contains the front matter associated with SPIE Proceedings Volume 10734, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

Electromagnetic coupled resonator arrays (CRAs) doped with a quantum two-level system allow for the quantum simulation of a Mott-insulator to superfluid phase transition. We demonstrate that the order of this simulated phase transition depends on the type of dynamics. Thus, a first order like phase transition can be induced by a quench dynamics, while a second order like phase transition is produced by an adiabatic dynamics. In addition, we show that the underlying macroscopic behavior of the phase transition in other many body systems, such as domain nucleation and phase coexistence, can also be observed in CRAs. This universal behavior emerges from the light-matter interaction and the topology of the array. Therefore, the latter can be used to manipulate the photonic transport properties of the simulated super fluid phase.

The field of photonics has made tremendous progress in connecting spatio-temporal measurements of new quantum materials, including 2D plasmonics, Moire structure localized potentials and Weyl semimetals, to theoretical predictions. This talk will present a carrier-lifetime driven approach to quantum materials with a focus on theory and simulations of these, as relevant to quantum photonics and optics. A theoretical description of ultrafast-fast (attosecond - nanosecond) behavior of excited carrier dynamics in quantum materials involves two major ingredients: i) The optical response of the material (and its environment like the substrate or encapsulating layers) and ii) the dynamics of the excited carriers, including electron-electron and electron-phonon scattering. Here, I will discuss recent calculations and advances on both fronts from my group, with a particular emphasis on linking these calculations with experimental observations. Combining the power and possibilities of excited-state and heterostructure engineering with the collective and emergent properties of quantum materials, quantum-matter heterostructures open new directions in quantum photonics. The ability to design optoelectronic interactions (via vdW heterostructures) in 2D and 3D materials makes this platform extremely promising for atomistic control, design, and scaling of new photonic technologies.

We study computationally the 3-photon molecule generation through coherent scattering process in nonlinear quantum nanophotonics. Specifically, the molecule signature is confirmed with an imprinted π conditional phase shift by examining the wave function in both real- and frequency-space representation, and correlation functions g⁽³⁾ and g⁽²⁾. Moreover, we show that the correlation metrics for the three- and two-photon Fock state scattering also apply to a weak-coherent optical input, which describe well the recent experimental results in ultra-cold atomic gas. Our work opens up a new research direction of computational study for correlated three-photon scattering and transport processes. Generations of 3-photon molecule may tremendously enhance the three-photon fluorescence microscopy efficiency and facilitate the realization of deterministic quantum logic gates.

Thin films have attracted a great deal of attention within the nanophotonics community due to their ability to strongly confine and manipulate light on extreme subwavelength scales. Recent advances in nanotechnology now enable the fabrication of films with nanometer-scale thickness, which can potentially be used to further miniaturize the next generation of electronic and photonic devices. Nowadays, there exist many kinds of materials that can be structured into thin films. Noble metals (Cu, Ag, Au, ...) are a particularly interesting class of material for nanotechnology due to their appealing chemical and physical properties. However, in very small metallic structures, quantum mechanical effects play an important role in the dynamics of electrons and their interaction with external electromagnetic fields (light). These effects can become even more significant when dealing with nonlinear optical phenomena, which necessitate extremely intense optical fields. Here we investigate the linear and nonlinear optical response of thin metallic films consisting of a finite number of atomically-thin layers by adopting a quantum-mechanical description of the electron dynamics in the atomic planes of the metal layers. We consider films of noble metals characterized by a potential that captures important electronic band features, including the atomic periodicity across the films, electron spill-out, and surface states, all of which contribute significantly to the optical response associated with plasmon resonances. Self-consistent field calculations of the optical response are performed by solving the single-electron density matrix equation of motion perturbatively, which yields the linear optical response, while non-perturbative simulations in the time-domain enable study of extreme nonlinear optical phenomena, including saturable absorption and high-order harmonic generation. We identify a strong dependence on quantum-finite size effects in the optical response associated with plasmon resonances, both in the linear and nonlinear domains.

WITHDRAWAL NOTICE: This conference presentation, originally published on 9/18/18, was removed on 9/25/18 per author request.

Plasmons in highly-doped graphene offer the means to dramatically enhance light absorption in the atomically-thin material. Ultimately the absorbed light energy induces an increase in electron temperature, accompanied by large shifts in the chemical potential. This intrinsically incoherent effect leads to strong intensity-dependent modifications of the optical response, complementing the remarkable coherent nonlinearities arising in graphene due to interband transitions and anharmonic intraband electron motion. Here we show that the out-of-equilibrium electronic distribution induced by intense, resonant illumination of plasmons in nanostructured graphene results in a strong transient, incoherent nonlinear optical response that can dominate over the sought-after coherent nonlinear response. Under such conditions, our results indicate that the combined changes in electronic temperature and chemical potential effectively detune the graphene plasmon resonances from their linear-regime values, effectively enabling all-optical modulation. Additionally, a significant saturation of absorption is predicted to occur due to such incoherent processes. The relatively low electronic heat of graphene and the comparatively small number of electrons involved in its plasmons are ultimately responsible for this behavior, which limits the coherent nonlinear manipulation of optical pulses down to very short durations (below 100 fs), but opens new opportunities for transient plasmon-assisted light modulation, with potential uses in nonlinear nanophotonic devices such as optical switches and saturable absorbers. We anticipate that these findings will elucidate the role of coherent and incoherent nonlinearities for future studies and applications of plasmon-assisted nonlinear optics.

The resonant high-index nanostructures open opportunities for control many optical effects via optically-induced electric and magnetic Mie resonances, mostly localized inside the structures. Especial interest such nanostructures represent for quantum emitters placed inside, that makes possible enhancement of quantum source emission through resonant coupling to localized modes. We have proposed the concept of active dielectric nanoantennas based on nanodiamonds with embedded NV-centers. The study of theoretically dependence of optical properties of this system on the spectral position of the resonant modes has demonstrated that that at some sizes of the diamond spherical particles and certain position of the dipole in the sphere the Purcell factor can achieve the value of 30. We have demonstrated experimentally that the photoluminescence properties of the NV-centers can be controlled via scattering resonances and observed a decrease of the NV-centers lifetime in the studied diamond particles, as compared to nonresonant nanodiamonds. These results are in a good agreement with our theoretical calculations for the average Purcell factor for multiple NV-centers within a nanoparticle. The simplicity of the proposed concept compared to existing photonic cavity systems and applicability for a wide range of color centers in diamond make active diamond nanoantenna an effective tool for creating controllable emitting elements in the visible range for future nanophotonic devices.

High-quality sources of single photons are of paramount importance for quantum communication, sensing and metrology. To these ends, resonantly excited two-level systems have recently generated widespread interest. Nevertheless, for resonantly excited two-level systems, emission of a photon during the presence of the excitation laser pulse and subsequent re-excitation results in a degradation of the obtainable single-photon purity [1]. Here, we investigate a two-photon excitation scheme based on a three-level system formed by the bi-exciton - exciton cascade in a self-assembled quantum dot and demonstrate that it improves the multi-photon error rate by several orders of magnitude [2]. We support our experiments with a new theoretical framework and simulation methodology to understand few-photon sources. For a resonantly excited two-level system the multi-photon error rate scales linear with the pulse length [3]. In contrast, the two-photon excitation scheme exhibits a quadratic dependence, improving the obtainable multi-photon error rate by several orders of magnitude for short pulses. Moreover, the scheme is easy to implement and facilitates fast repetition rates in contrast to schemes involving three-level lambda-type systems that require re-pumping. Unlike resonant excitation of a two-level system, this scheme does not require the measurement technique of cross-polarized suppression to reject the excitation laser and, thus, enables a higher source brightness. Finally, the scheme is directly compatible with increasing the emission rate by Purcell enhancement. [1] K.A. Fischer et al. Nature Physics 13, 649-654 (2017) [2] L. Hanschke, et al. arXiv:1801.01672 (2018) [3] K.A. Fischer, et al. Quantum Science and Technology 3, 1 (2017)

Plasmonic nanostructures offer a wide variety of optical modes that can be harnessed for controlling different radiation properties of single-photon emitters. These effects are broadband and are of special interest for quantum emitters at room temperature. We study these effects using nitrogen-vacancies in diamond nanocrystals. Extremely confined optical modes in hybrid cavity/nanoantenna structures lead to unprecedented levels of single-photon brightness at room temperature in the range of tens of million photons per second. Metamaterials offer highly broadband non-resonant brightness enhancement over 200 nm for all dipole orientations, which can be applied to emitters with broad spectrum or widely inhomogeneous line distributions. Dielectric bullseye corrugations on planar plasmonic films allow to reach highly directional Purcell enhanced emission within 5 degrees half-angle.

The extreme spatial light confinement provided by graphene plasmons is anticipated to facilitate strong light-matter coupling through their resonant interaction with proximal quantum emitters [1], as well as to push the remarkably-high intrinsic nonlinear response of the carbon layer to record-high levels [2]. Plasmon resonance frequencies in graphene typically lie in the infrared and terahertz regimes, which is ideal for probing the vibrational fingerprints of nanometric biomolecules [3], but energetically mismatched from the transitions of robust, solid-state single-photon sources such as quantum dots and nitrogen-vacancy centers. Here we propose to utilize the near-field generated by the nonlinear optical response of resonantly-driven localized graphene plasmons to achieve strong coupling with proximal quantum emitters. Specifically, we predict that the near fields produced through mid-infrared driven plasmon-assisted third-harmonic generation in a doped graphene nanodisk are sufficiently large as to yield observable Rabi splitting in two- or multi-level quantum emitters operating in the near-infrared regime. In this scenario, the electrostatic tunability of graphene plasmon resonances can be exploited first to target the relevant electronic transition of a particular quantum emitter and later to actively control its absorption and radiative emission. We envision potential applications for the proposed nonlinear graphene plasmon-assisted strong coupling scheme in nonlinear sensing and as actively-controllable elements in quantum information networks.

An important result from quantum optics and condensed matter physics is the use of radiation-matter interaction to produce light with specific characteristics. In this work, we study a nonstationary atom-cavity system and characterize the physical properties of the emitted light. In particular we deal with a Fabry-Perot cavity with a moving mirror which has an embedded two-level system. The study of the statistical properties is done by means of the second-order correlation function with zero delay, which allows to classify the light emitted by the physical system in three different statistical regimes (Poissonian, sub-Poissonian and super-Poissonian) depending on the relationship between the variance and the mean of the photon number distribution. Therefore, in a range of parameters for which the extraction of excitations from the quantum vacuum is evident, we find that the non-classicality of the emitted light depends strongly on the relationship between the radiation-matter coupling constant and the frequency of modulation of the length of the cavity.

Metal nanocrystals and semiconductor quantum dots have the ability to absorb and scatter light very efficiently. This study concerns special designs of hybrid nanostructures with electromagnetic hot spots, where the electromagnetic field becomes strongly enhanced and concentrated. Overall, plasmonic nanostructures with hot spots demonstrate strongly amplified optical and energy-related effects: (1) Using nanoparticle arrays made of different metals, one can transfer plasmonic signals coherently and with small losses [1]. (2) Plasmonic hot spots efficiently generate energetic electrons, which can be used for photochemistry and photodetection [2,3]. (3) Nanostructures with hot spots can strongly enhance the optical generation of heat, and also confine high photo-temperatures in small volumes [4,5,6]. (4) Colloidal nanocrystal assemblies and metasurfaces with plasmon resonances allow us to strongly enhance chiral optical responses (circular dichroism) of biomolecules and drugs [7,8,9]. [1] E.-M. Roller, et al., Nature Physics, 13, 761 (2017). [2] A.O. Govorov, H. Zhang, H.V. Demir and Y. K. Gun’ko, Nano Today 9, 85 (2014). [3] H. Harutyunyan, et al., Nature Nanotech. 10, 770 (2015). [4] A. O. Govorov and H. Richardson, Nano Today 2, 20 (2007). [5] C. Jack, et al., Nat. Commun. 7, 10946 (2016). [6] X.-T. Kong, et al., Nano Letters, DOI: 10.1021/acs.nanolett.7b05446 [7] A. O. Govorov, et al., Nano Letters 10, 1374–1382 (2010). [8] A. Kuzyk, et al., Nature 483, 311 (2012). [9] X.-T. Kong, et al., Nano Letters 17, 5099–5105 (2017).

Calculations are presented of vibrational absorption spectra for energy minimized structures of Si_xO_y-nH₂O molecular clusters using density function theory (DFT). DFT can provide interpretation of absorption spectra with respect to molecular structure for excitation by electromagnetic waves at frequencies within the IR range. The absorption spectrum corresponding to excitation states of Si_xO_y-nH₂O molecular clusters consisting of relatively small numbers of atoms should be associated with response features that are intermediate between that of isolated molecules and that of a bulk system. DFT calculated absorption spectra represent quantitative estimates that can be correlated with additional information obtained from laboratory measurements. The DFT software GAUSSIAN was used for the calculations of excitation states presented here.

In Photo-induced Force Microscopy (PiFM) the near-field signal resulting from the surface illumination is detected via the interaction with the AFM cantilever. Unlike conventional Near-field Scanning Optical Microscopes (NSOM), both fiber-based and scattering-based, where much research is dedicated to suppress the background signal, in PiFM, no light signal is detected. In this sense PiFM is a light-background-free optical nano-spectroscopy technique that is promising for broadband operation and relaxes many of the illumination constraints of other NSOM techniques. I will first introduce tests experiments that highlight the working principles behind PiFM. Then, I will show results from ongoing experiments of PiFM on different materials, ranging from photo-sensitive polymers to 2D van der Waals materials.

In this paper, we study the statistical properties of light generated by two different types of quantum emitters embedded in an optical micro-cavity. These emitters are a single quantum dot (QD) and an artificial molecule (AM), which is made by two interacting QDs. The study of the statistical properties is done by means of the second-order correlation function, which can be calculated using the elements of the density matrix operator. Some non-Hamiltonian processes are considered such as incoherent pumping of photons, spontaneous emission, decay in leaky modes, phonon assistance to the main QD, and phonon assistance to the tunnelling mechanism. The effect of each one of those mechanisms in the emission properties of the system is analysed for a certain range of parameters. As a result, we observe that the tunnelling mechanism, as well as the phonon assistance mechanism to the main QD, are processes that can favour anti-bunching in the emitted photons. For the tunnelling phonon assistance, we find that these mechanisms attest against the non-classical character of the photons, changing its statistics by increasing the value of the second-order correlation function. However, the effect of the three mechanisms acting together on the system is a net diminish of the second-order correlation function, in comparison with the same system when all the mechanisms are turned off.

The spin-optical properties of nitrogen-vacancy (NV) centers in diamond have been demonstrated to enable a plethora of applications ranging from nanoscale sensing to quantum information technologies. The conventional design of NV-based devices requires separate infrastructures for delivering microwave (MW) excitation and guiding/collecting fluorescence signals. Typically, one fabricates dielectric waveguides or lenses next to metallic MW antennae. Here we showed that the device compactness can be substantially improved by the integration of NV centers with channel plasmonic waveguides milled in an optically thick metal layer that simultaneously acts as a MW antenna. The use of highly conductive plasmonic materials allows to fabricate monolithic ultra-compact structures supporting propagation of both MW and optical signals. We demonstrated optical readout of spin resonance by collecting channel plasmon polaritons scattered from the waveguide end.

An efficient silicon-based light source presents an unreached goal in the field of photonics, due to Silicon’s indirect electronic band structure preventing direct carrier recombination and subsequent photon emission. Here we utilize inelastically tunneling electrons to demonstrate an electrically-driven light emitting silicon-based tunnel junction operating at room temperature. We show that such a junction is a source for plasmons driven by the electrical tunnel current. We find that the emission spectrum is not given by the quantum condition where the emission frequency would be proportional to the applied voltage, but the spectrum is determined by the spectral overlap between the energy-dependent tunnel current and the modal dispersion of the plasmon. Experimentally we find the highest light outcoupling efficiency corresponding to the skin-depth of the metallic contact of this metal-insulator-semiconductor junction. Distinct from LEDs, the temporal response of this tunnel source is not governed by nanosecond carrier lifetimes known to semiconductors, but rather by the tunnel event itself and Heisenberg’s uncertainty principle. Finally We discuss a path for single photon emission via the Coulomb blockade effect leading to single electron tunneling.

Microscopic dynamics of plasmonic systems characterized by sub-nanometer gaps can be crucial to accurately describe their macroscopic optical properties. First-principle quantum mechanical approaches, such as Time-Dependent Density Functional Theory (TD-DFT), can give a very good approximation although their applicability is often limited to very small systems due to computational costs. Quantum hydrodynamic theory (QHT) is a promising tool which can efficiently predict the optical response of multiscale plasmonic systems. We apply this theory to investigate plasmonic response of spherical nanomatryoshkas (NMs), which are concentric core-shell structures, for Au and Na metals in the quantum tunneling regime. The results obtained for Au NMs are in a very good agreement with those of TD-DFT, already reported in the literature. We also study optical properties of quite big systems, both for Au and Na, whose sizes make them inaccessible for DFT calculations. We analyze the impact of core-shell spacing on near-field and far-field optical behavior of these systems and find that the QHT method predicts the nonlocal and quantum effects in multiscale plasmonic systems in an efficient manner. A systematic comparison between the local response, Thomas-Fermi and QHT approximations has also been presented. The results show that as the core-shell distance decreases the nonlocal or quantum effects strongly influence the plasmonic properties of these systems which can be nicely described by the QHT. For numerical implementation of these structures, we fully exploit the symmetry of the geometry and use a 2.5D simulation technique which reduces the computational efforts to a great extent.

Strong interaction between light and a single quantum emitter is pivotal to many applications, including single photon sources and quantum information processing. Typically, plasmonic antennas or optical cavities are used to boost this interaction. The former can focus light in a deeply subwavelength region, whereas the latter can store light for up to billions of oscillations. In our work, we combine these two opposite elements into a single coupled system. First, we show theoretically [1] that hybrid cavity-antenna systems can achieve Purcell enhancements far exceeding those of the bare cavity and antenna, and can do so at any desired bandwidth. This requires a delicate balance between spoiling the cavity with the antenna on the one hand, and cooperative and interference effects on the other. We then present our experimental results on hybrid systems using a whispering-gallery mode cavity and an aluminum plasmonic antenna. Using taper-coupled excitation of the hybrid mode, we study quality factors and radiation patterns, demonstrating that we can control the antenna-cavity coupling strength by varying their respective frequency detuning. We show that we can achieve modes that retain quality factors around 10^4, while creating a strongly localized field around the antenna. As such, we can exploit the benefits of plasmonic confinement without suffering from the usual losses. Finally, we present first studies of fluorescent emitters coupled to the hybrid modes. [1] Doeleman, H. M., Verhagen, E., & Koenderink, A. F., "Antenna–Cavity Hybrids: Matching Polar Opposites for Purcell Enhancements at Any Linewidth." ACS Photonics 3.10 (2016): 1943-1951.