This PDF file contains the front matter associated with SPIE Proceedings Volume 10359, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

Atomically thin materials such as graphene and molecular aromatic hydrocarbon exhibit unique optical properties that allow us to control the flow of light down to the atomic scale. These materials can sustain collective electron resonances -plasmons- involving a relatively small number of electrons, therefore enabling unprecedented electrical, magnetic, optical, and thermal control of those properties. In this talk, I will review recent progress in this field and present illustrative examples of nonlinear, quantum, and ultrafast phenomena in these materials, along with applications to optical sensing, optoelectronics, and quantum optics.

Optically excited plasmonic nanostructures display remarkable electron dynamics in the form of coherent electron displacement motion, as well as efficient generation of non-thermal ‘hot electrons’ with large kinetic energy. Here, we provide a theoretical and experimental overview of our studies of photo-induced charge transport across plasmonic tunneling junctions composed of nanoscale metallic gaps, as a strategy for taking advantage of such electron motion for optoelectronic energy conversion. In symmetric plasmonic tunneling gaps the energetic distribution of electrons due to photo-induced thermalization and hot electron generation is insufficient for significant electrical currents, either through excitation over the interface potential barrier, or via tunneling that exhibits a net preference for the direction of charge transfer. However, asymmetric resonant structures can provide optical absorption, photo-excitation and time-dependent electric fields that induce significant temperature gradients and local variations in the hot electron population. Such asymmetry can be used to promote unidirectional tunneling transport currents with significant enhancement compared with conventional photoelectron and thermionic emission (~ 10^15 enhancement), and thus comprises an intriguing mechanism for providing electrical work. This presentation will introduce the theoretical framework of tunneling phenomena associated with photon-induced hot electrons in plasmonic structures, including principles of electron distribution under photon excitation, strategies for amplifying hot electron generation (e.g. manipulating hot spots in nano-antennas) and provide a mechanistic quantum model of power conversion devices based on unidirectional electron tunneling across nanoscale plasmonic junctions. We also report on initial transport measurements of plasmonic tunnel junctions that exhibit optical power conversion by this method.

Vacuum consists of a bath of balanced and symmetric positive and negative frequency fluctuations. Media in relative motion or accelerated observers can break this symmetry and preferentially amplify negative frequency modes as in Quantum Cherenkov radiation and Unruh radiation. Here, we show the existence of a universal negative frequency-momentum mirror symmetry in the relativistic Lorentzian transformation for electromagnetic waves. We show the connection of our discovered symmetry to parity-time (PT) symmetry in moving media and the resulting spectral singularity in vacuum fluctuation related effects. We prove that this spectral singularity can occur in the case of two metallic plates in relative motion interacting through positive and negative frequency plasmonic fluctuations (negative frequency resonance). Our work paves the way for understanding the role of PT-symmetric spectral singularities in amplifying fluctuations and motivates the search for PT-symmetry in novel photonic systems. [1] arXiv:1612.02050 [physics.optics]

Over the past decades, alkali atoms have been the subject of intensive and diverse research, ranging from fundamental studies on ultra-cold atoms and Bose-Einstein condensates to technological applications. Since they possess only a single valance s-electron, the alkali atoms manifest a simple low-lying electronic structure compared to other atoms. Moreover, unlike conventional solid state systems their dispersion-free features make them an ideal candidate for sensing applications and referencing tasks. These two features have introduced alkali atoms as promising quantum emitters for the new paradigm of hybrid quantum optics and quantum electrodynamics. This new concept benefits from the existing integrated photonics technology for squeezing and confining the light in sub-wavelength scales to substantially enhance the light-atom interaction. The hybrid chip is envisioned to have light sources, waveguides, devices, and detectors to realize a complex quantum network down to a single photon level. In this talk I will discuss about our recent theoretical and experimental works on atomic vapor spectroscopy in the vicinity of the plasmonic and nanophotonic devices. I start from a density matrix-based formalism describing the evolution of Rb vapor atomic levels, excited with an incoherent pump and coupled to a plasmonic lattice. When designed properly, the lattice plasmon mode efficiently captures the spontaneously emitted photons from the excited Rb atoms and a coherent coupling between the lattice mode and the atomic levels would occur. I will elaborate on the effect of pumping rate and decoherence on the steady state of the hybrid system and the feasibility of achieving a lasing state. In the second part of the talk I will present the results of our experiments on Rb vapor coupled to such a plasmonic lattice. Starting from the pumping mechanism, I describe the collisional scheme we employed to transfer the excited Rb atoms from (_^5)P_(3/2) to(_^5)P_(1/2) , hence achieving a population inversion between P and S levels and an optical gain at 795 nm, eventually. I present the experimental results of this atomic vapor interaction with a plasmonic lattice resonating at 795 nm. The spectroscopy of Rb cloud modified with tightly squeezed and enhanced field of the lattice plasmons shows the clear signature of Fano resonances in the passive gas, followed by amplified spontaneous emission in the active gas and the lasing at higher pumping powers. The results of this study would pave the way toward hybrid atom-quantum photonic chips.

Quantum state tomography and the reconstruction of the photon number distribution are techniques to extract the properties of a light field from measurements of its mean and fluctuations. These techniques are particularly useful when dealing with macroscopic or mesoscopic systems, where a description limited to the second order autocorrelation soon becomes inadequate. In particular, the emission of nonclassical light is expected from mesoscopic quantum dot systems strongly coupled to a cavity or in systems with large optical nonlinearities. We analyze the emission of a quantum dot-semiconductor optical amplifier system by quantifying the modifications of a femtosecond laser pulse propagating through the device. Using a balanced detection scheme in a self-heterodyning setup, we achieve precise measurements of the quadrature components and their fluctuations at the quantum noise limit1. We resolve the photon number distribution and the thermal-to-coherent evolution in the photon statistics of the emission. The interferometric detection achieves a high sensitivity in the few photon limit. From our data, we can also reconstruct the second order autocorrelation function with higher precision and time resolution compared with classical Hanbury Brown-Twiss experiments.

Issues of a fundamental quantum origin exert a significant effect on the output mode structures in optically parametric processes. An assumption that each frequency conversion event occurs in an infinitesimal volume produces uncertainty in the output wave-vector, but a rigorous, photon-based theory can provide for a finite conversion volume. It identifies the electrodynamic mechanisms operating within the corresponding region of space and time, on an optical wavelength and cycle timescale. Based on quantum electrodynamics, this theory identifies specific material parameters that determine the extent and measure of delocalized frequency conversion, and its equations deliver information on the output mode structures. The results also indicate that a system of optimally sized nanoparticles can display a substantially enhanced efficiency of frequency conversion.

Quantum dots are excellent solid-state quantum sources, because of their stability, their narrow spectral linewidth, and radiative lifetime in the range of 1ns. Most importantly, they can be integrated into more complex nanophononics devices, to realize high quality quantum emitters of single photons or entangled photon sources. Recent progress in nanotechnology materials and devices has opened a number of opportunities to increase, optimize and ultimately control the emission property of single quantum dot. In this work, we present an approach that combines the properties of quantum dots with the flexibility of light control offered by nanoplasmonics and metamaterials structuring. Specifically, we show the nanophotonic enhancement of two types of quantum dots devices. The quantum dots are inserted into optical-positioned micropillar cavities, or decorated on the facets of core-shell GaAs/AlGaAs nanowires, fabricated with a bottom-up approach. In both cases, the metallic nanofeatures, which are designed to control the emission and the polarization state of the emitted light, are realized via direct electron-beam-induced deposition. This approach permits to create three-dimensional features with nanometric resolution and positional accuracy, and does not require wet lithographic steps and previous knowledge of the exact spatial arrangement of the quantum devices.

Metasurfaces have traditionally employed building blocks with physically intuitive optical responses. Many of these concepts utilize dielectric posts, which serve as waveguides and are stitched together with sufficient spacing to minimize coupling between adjacent elements. These design principles can produce single wavelength devices with good performance, but are difficult to generalize to multi-wavelength devices with exceptional performance. We show that concepts in inverse design can be used to produce dielectric metasurfaces with capabilities that exceed the current state-of-the-art. With swarm and topology optimization, we incorporate optical coupling between waveguide elements in the device designs, which yield physically non-intuitive mode profiles and coupling dynamics. To demonstrate the power and versatility of our design approach, we fabricate silicon devices that can efficiently deflect light to 75 degree angles and multi-functional devices that can steer beams to different diffraction orders based on wavelength. We also show that single crystal silicon can be used to realize efficient metasurface devices across the entire visible spectrum, ranging from 480 to 700 nanometers. Alternative forms of silicon, such as polycrystalline and amorphous silicon, suffer from higher absorption losses and do not yield efficient metasurfaces across this wavelength range. We envision that metasurfaces based on inverse design will serve as a hardware platform for the efficient routing, sorting, and manipulation of single or few photons for quantum optics applications.

The investigation of surfaces and thin films is of particular interest in current research as it provides a basis for a multiplicity of applications such as waveguides, sensors, solar cells and optoelectronics. The losses of light emitting structures, here CdSe nano-platelets, can be reduced by harmonizing the orientation of the transition dipoles with the optical mode that the light is coupled to. The electronic structure of the emitting nanoparticle can be optimized via its shape and the density of states strongly depends on the dielectric function of the environment which can be tuned to modify the emission characteristics.

Surface-Enhanced Raman Scattering (SERS) is a fundamental spectroscopic technique that allows to access the rich vibrational structure of molecules. A typical SERS configuration with a molecule located in a plasmonic cavity acting as an optical nanoantenna enhances the vibrational (Stokes or anti-Stokes) signal of the molecule. A number of recent implementations of Raman experiments in plasmonic nanocavities appear to provide results which escape the standard description of the Raman process based on the classical treatment of the electromagnetic fields enhancement inside the cavity. We establish a novel analogy between non-resonant SERS in molecular spectroscopy and typical optomechanical processes. By adopting an optomechanical hamiltonian which describes the interaction between cavity plasmons and molecular vibrations, we are able to trace the quantum dynamics of both plasmons and vibrations in a SERS process. The solution of the master equation of this optomechanical hamiltonian allows to identify novel quantum effects such as the existence of different regimes of molecular vibrational build-up: a thermal vibrational regime, a vibrational pumping regime, and a strongly nonlinear vibrational regime, which emerge as a consequence of the quantum dynamics induced by the optomechanical interaction. Correlations between the Stokes and anti-Stokes Raman signals can also be traced for different temperatures and pumping powers. The presence of strong optomechanical effects in Raman has been recently addressed experimentally in special "picocavities" formed by a few metallic atoms in a plasmonic cavity. The strong optomechanical coupling achieved in this situation is found to activate the pumping regime in the Raman signal, thus corroborating the validity of this description.

We present the first investigation of optomechanics in an integrated one-dimensional gallium phosphide (GaP) photonic crystal cavity. The devices are fabricated with a newly developed process flow for integration of GaP devices on silicon dioxide (SiO₂) involving direct wafer bonding of an epitaxial GaP/Al_xGa_1-xP/GaP heterostructure onto an oxidized silicon wafer. Device designs are transferred into the top GaP layer by inductively-coupled-plasma reactive ion etching and made freestanding by removal of the underlying SiO₂. Finite-element simulations of the photonic crystal cavities predict optical quality factors greater than 106 at a design wavelength of 1550 nm and optomechanical coupling rates as high as 900 kHz for the mechanical breathing mode localized in the center of the photonic crystal cavity. The first fabricated devices exhibit optical quality factors as high as 6.5 × 10⁴, and the mechanical breathing mode is found to have a vacuum coupling rate of 200 kHz at a frequency of 2.59 GHz. These results, combined with low two-photon absorption at telecommunication wavelengths and piezoelectric behavior, make GaP a promising material for the development of future nanophotonic devices in which optical and mechanical modes as well as high-frequency electrical signals interact.

Integrated quantum photonics imposes very stringent and often contradictory requirements on the design of integrated optical components. Many material platforms have been proposed and developed to host the future quantum optical systems. All of them feature fundamental limitations that invite to consider more complex, hybrid platforms. In this talk, we focus on the use of plasmonic materials for realizing quantum devices that possess properties not available with only dielectric materials. We present our work on fast room-temperature single-photon sources and specifically address the problem of efficient outcoupling of the plasmonic modes to the far-field. We demonstrate optical spin-state readout from nitrogen-vacancies in nanodiamonds through surface plasmon-polaritons and show that quantum registers and sensors based on these color centers can operate within nanoscale optical circuits. We also discuss how our novel approach combining plasmonics with optofluidics helps achieving fast and deterministic positioning of nanodiamonds in the vicinity of plasmonic antennas. This result promises scalable assembly techniques for more complex nanophotonic systems. With these new functionalities, plasmonic devices could play a decisive role in the engineering of tomorrow’s quantum photonic systems.

We show that inelastically-scattering tunnel electrons are a source for electric plasmon generation. We experimentally demonstrate such electrically-driven light-emitting tunnel junction by forward biasing a Fermi sea against a doped semiconductor across a nanometer-thin tunnel gap. Light emission at room temperature is found in the visible frequency range corresponding to a spectral power dependency of the tunnel current and the plasmonic mode. The response time (speed) of such a tunnel junction scales inverse exponentially with the tunnel gap thickness approaching Tpbs for <0.5nm thin gaps. Lastly, since tunneling allows for single-charge events, the possibility for single-photon generation is expected.

Plasmons in atomic-scale structures exhibit intrinsic quantum phenomena related to both the finite confinement that they undergo and the small number of electrons on which they are supported. Their interaction with two-level emitters is also evidencing strong quantum effects. In this talk I will discuss several salient features of graphene plasmons in this context, and in particular their ability to mediate ultrafast heat transfer, the generation of high harmonics, their interaction with molecules and quantum emitters, and their extreme nonlinearity down to the single-photon level.

We discuss the topological properties of graphene superlattices excited by ultrafast circularly-polarized laser pulses with strong electric field amplitude, aiming to directly observe of the Berry phase, a geometric quantum phase encoded in the graphene’s electronic wave function. As a continuing research on our recent paper, Phys. Rev. B 96, 075409, we aim to show that the broken symmetry system of graphene superlattice and the Bragg reflection of electrons creates diffraction and “which way” interference in the reciprocal space reducing the geometrical phase shift and making it directly observable in the electron interferograms. Such a topological phase shift acquired by a carrier moving along a closed path of crystallographic wave vector is predictably observable via time and angle resolved photoemission spectroscopy (tr-ARPES). We believe that our result is an essential step in control and observation of ultrafast electron dynamics in topological solids and may open up a route to all-optical switching, ultrafast memories, and petahertz-scale information processing technologies.