121 research outputs found
Direct amplitude-phase near-field observation of higher-order anapole states
Anapole states associated with the resonant suppression of electric-dipole
scattering exhibit minimized extinction and maximized storage of
electromagnetic energy inside a particle. Using numerical simulations, optical
extinction spectroscopy and amplitude-phase near-field mapping of silicon
dielectric disks, we demonstrate high-order anapole states in the near-infrared
wavelength range (900-1700 nm). We develop the procedure for unambiguously
identifying anapole states by monitoring the normal component of the electric
near-field and experimentally detect the first two anapole states as verified
by far-field extinction spectroscopy and confirmed with the numerical
simulations. We demonstrate that higher order anapole states possess stronger
energy concentration and narrower resonances, a remarkable feature that is
advantageous for their applications in metasurfaces and nanophotonics
components, such as non-linear higher-harmonic generators and nanoscale lasers
Optical reconfiguration and polarization control in semi-continuous gold films close to the percolation threshold
Controlling and confining light by exciting plasmons in resonant metallic
nanostructures is an essential aspect of many new emerging optical
technologies. Here we explore the possibility of controllably reconfiguring the
intrinsic optical properties of semi-continuous gold films, by inducing
permanent morphological changes with a femtosecond (fs)-pulsed laser above a
critical power. Optical transmission spectroscopy measurements show a
correlation between the spectra of the morphologically modified films and the
wavelength, polarization, and the intensity of the laser used for alteration.
In order to understand the modifications induced by the laser writing, we
explore the near-field properties of these films with electron energy-loss
spectroscopy (EELS). A comparison between our experimental data and full-wave
simulations on the exact film morphologies hints toward a restructuring of the
intrinsic plasmonic eigenmodes of the metallic film by photothermal effects. We
explain these optical changes with a simple model and demonstrate
experimentally that laser writing can be used to controllably modify the
optical properties of these semi-continuous films. These metal films offer an
easy-to-fabricate and scalable platform for technological applications such as
molecular sensing and ultra-dense data storage.Comment: Supplementary materials available upon request ([email protected]
Exploring More-Coherent Quantum Annealing
In the quest to reboot computing, quantum annealing (QA) is an interesting
candidate for a new capability. While it has not demonstrated an advantage over
classical computing on a real-world application, many important regions of the
QA design space have yet to be explored. In IARPA's Quantum Enhanced
Optimization (QEO) program, we have opened some new lines of inquiry to get to
the heart of QA, and are designing testbed superconducting circuits and
conducting key experiments. In this paper, we discuss recent experimental
progress related to one of the key design dimensions: qubit coherence. Using
MIT Lincoln Laboratory's qubit fabrication process and extending recent
progress in flux qubits, we are implementing and measuring QA-capable flux
qubits. Achieving high coherence in a QA context presents significant new
engineering challenges. We report on techniques and preliminary measurement
results addressing two of the challenges: crosstalk calibration and qubit
readout. This groundwork enables exploration of other promising features and
provides a path to understanding the physics and the viability of quantum
annealing as a computing resource.Comment: 7 pages, 3 figures. Accepted by the 2018 IEEE International
Conference on Rebooting Computing (ICRC
Plasmonic black gold by adiabatic nanofocusing and absorption of light in ultra-sharp convex grooves
White light generation and anisotropic damage in gold films near percolation threshold
Strongly enhanced and confined electromagnetic fields generated in metal
nanostructures upon illumination are exploited in many emerging technologies by
either fabricating sophisticated nanostructures or synthesizing colloid
nanoparticles. Here we study effects driven by field enhancement in vanishingly
small gaps between gold islands in thin films near the electrically determined
percolation threshold. Optical explorations using two-photon luminescence (TPL)
and near-field microscopies reveals super-cubic TPL power dependencies with
white-light spectra, establishing unequivocally that the strongest TPL signals
are generated with close to the percolation threshold films, and occurrence of
extremely confined (~ 30 nm)and strongly enhanced (~ 100 times) fields at the
illumination wavelength. For linearly polarized and sufficiently powerful
light, we observe pronounced optical damage with TPL images being sensitive to
both wavelength and polarization of illuminating light. We relate these effects
to thermally induced morphological changes observed with scanning electron
microscopy images. Fascinating physics involved in light interaction with
near-percolation metal films along with their straightforward and scalable
one-step fabrication procedure promises a wide range of fascinating
developments and technological applications within diverse areas of modern
nanotechnology, from bio-molecule optical sensing to ultra-dense optical data
storage.Comment: 42 pages in total of the main (27 pages) and supplementary (15 pages)
material with 4 main and 10 supplementary figure
Near- and far field spectroscopy of semi-continuous gold films with optically induced anisotropy.
- …