Seeing Quantised Polaritons without Condensation

Exciton polaritons in high quality semiconductor microcavities can travel long macroscopic distances (>100μm) due to their ultra-light effective mass. The polaritons are repelled from the optically-pumped exciton reservoirs where they are formed, however their spatial dynamics is not as expected for point-like particles. Instead we show polaritons emitted into waveguides travel orthogonally to the repulsive potential gradient, and can only be explained if they are emitted as macroscopic delocalised quantum particles, even before they form Bose condensates

Localized Nanogap Plasmonics for Extreme nanophotonics from ultrathin metallic gaps

Ultrathin dielectric gaps between metals can trap plasmonic optical modes with surprisingly low loss and with volumes below 1nm3. We review the origin and subtle properties of these modes, and show how they can be well accounted for by simple models. Particularly important is the mixing between radiating antenna and confined nanogap modes, which is extremely sensitive to precise nano-geometry, right down to the single atom level. Coupling nanogap plasmons to electronic and vibronic transitions yields a host of phenomena including single-molecule strong coupling and molecular optomechanics, opening access to atomic-scale chemistry and material science, and quantum metamaterials. Ultimate low-energy devices such as robust bottom-up assembled single-atom switches are thus in prospect

Tracking Optical and Electronic Behaviour of Quantum Contacts in Sub-Nanometre Plasmonic Cavities.

Plasmonic interactions between two metallic tips are dynamically studied in a supercontinuum dark-field microscope and the transition between coupled and charge-transfer plasmons is directly observed in the sub-nm regime. Simultaneous measurement of the dc current, applied force, and optical scattering as the tips come together is used to determine the effects of conductive pathways within the plasmonic nano-gap. Critical conductances are experimentally identified for the first time, determining the points at which quantum tunnelling and conductive charge transport begin to influence plasmon coupling. These results advance our understanding of the relationship between conduction and plasmonics, and the fundamental quantum mechanical behaviours of plasmonic coupling.The authors would like to acknowledge Nanotools GmbH for their contributions and support to this project. We acknowledge EPSRC Grants No. EP/G060649/1, No. EP/L027151/1, and No. EP/K028510/1, ERC Grant No. LINASS 320503, and Ikerbasque. RWB thanks Queens’ College, Cambridge and the Royal Commission for the Exhibition of 1851 for financial support.This is the final version of the article. It first appeared from Nature Publishing Group via http://dx.doi.org/10.1038/srep3298

Carbon nanotubes: Wiry matter-light coupling

Coaxing light and matter to interact strongly enough to fully mix into coupled states has been the focus for scientists bridging photonics, materials and chemistry over the past three decades. Admixing states creates new quasiparticles with unusual material properties. Their pursuit is relevant to efficient low-threshold lasers, nonlinear optical materials for switching that outperform anything previously available, and solid-state Bose–Einstein condensates that underpin quantum technologies. Writing in Nature Materials, Jana Zaumseil and colleagues1 have developed a way to incorporate size-selected carbon nanotubes into micrometre-sized photonic cavities, fully mixing the excitons with light at room temperature and, crucially, demonstrating their simple electrical excitation

Controlling Nanowire Growth by Light.

Individual Au catalyst nanoparticles are used for selective laser-induced chemical vapor deposition of single germanium nanowires. Dark-field scattering reveals in real time the optical signatures of all key constituent growth processes. Growth is initially triggered by plasmonic absorption in the Au catalyst, while once nucleated the growing Ge nanowire supports magnetic and electric resonances that then dominate the laser interactions. This spectroscopic understanding allows real-time laser feedback that is crucial toward realizing the full potential of controlling nanomaterial growth by light.We acknowledge financial support from EPSRC Grant EP/G060649/1, EP/L027151/1, EP/G037221/1, EPSRC NanoDTC, and ERC Grant LINASS 320503. S.H. acknowledges funding from ERC Grant InsituNANO 279342.This is the author accepted manuscript. The final version is available from ACS via http://dx.doi.org/10.1021/acs.nanolett.5b0295

Motile Artificial Chromatophores: Light-Triggered Nanoparticles for Microdroplet Locomotion and Color Change

Gold nanoparticles coated with a poly(N-isopropylacrylamide) (pNIPAM) shell undergo reversible dis/assembly below and above the critical temperature of 32°C. Loading these particles into microdroplets at high density creates light-driven artificial chromatophores. Triggering the nanoparticle assembly gives dramatic color changes from nanoparticle localization at the base of the droplets, resembling zebrafish melanophores. These reversible chromatophore states can be switched by both bulk and optical heating, explored here in individual microdroplets and in large cm^2 areas of close-packed droplets. Illuminating chromatophores off-center with a tightly focused beam results in droplet locomotion via two separate mechanisms, Marangoni interfacial shear and gas bubble propulsion, depending on optical power.ER

Bio-inspired band-gap tunable elastic optical multilayer fibers.

The concentrically-layered photonic structure found in the tropical fruit Margaritaria nobilis serves as inspiration for photonic fibers with mechanically tunable band-gap. The fibers show the spectral filtering capabilities of a planar Bragg stack while the microscopic curvature decreases the strong directional chromaticity associated with flat multilayers. Elongation of the elastic fibers results in a shift of the reflection of over 200 nm.Financial support from the US Air Force Offi ce of Scientifi c Research Multidisciplinary University Research Initiative under award numbers FA9550-09-1-0669-DOD35CAP, FA9550-10-1-0020 and the UK Engineering and Physical Sciences Research Council EP/G060649/1 is gratefully acknowledged. M.Ko. acknowledges the fi nancial support from the Alexander von Humboldt Foundation in form of a Feodor Lynen postdoctoral research fellowship. This work was performed in part at the Center for Nanoscale Systems (CNS), a member of the National Nanotechnology Infrastructure Network (NNIN), which is supported by the National Science Foundation under NSF award no. ECS-0335765. CNS is part of Harvard University

Spatiotemporal Dynamics and Control of Strong Coupling in Plasmonic Nanocavities

© 2017 American Chemical Society. In the light-matter strong coupling regime, the excited state of quantum emitters is inextricably linked to a photonic mode, leading to hybrid states that are part light and part matter. Recently, there has been a huge effort to realize strong coupling with nanoplasmonics, since it provides a versatile environment to study and control molecules in ambient conditions. Among the most promising designs are plasmonic nanocavities that confine light to unprecedentedly small volumes. Such nanocavities, though, support multiple types of modes, with different field profiles and radiative decay rates (bright and dark modes). Here, we show theoretically that the different nature of these modes leads to mode beating within the nanocavity and the Rabi oscillations, which alters the spatiotemporal dynamics of the hybrid system. By specifically designing the illumination setup, we decompose and control the dark and bright plasmon mode excitation and therefore their coupling with quantum emitters. Hence, this work opens new routes for dynam ically dressing emitters, to tailor their hybrid states with external radiation

Magneto-optical coupling in whispering-gallery-mode resonators

We demonstrate that yttrium iron garnet microspheres support optical whispering gallery modes similar to those in non-magnetic dielectric materials. The direction of the ferromagnetic moment tunes both the resonant frequency via the Voigt effect as well as the degree of polarization rotation via the Faraday effect. An understanding of the magneto-optical coupling in whispering gallery modes, where the propagation direction rotates with respect to the magnetization, is fundamental to the emerging field of cavity optomagnonics.Engineering and Physical Sciences Research Council (Grant IDs: EP/M50693X/1, EP/L027151/1), European Research Council (Grant ID: 648613), Hitachi (research fellowship), Royal Society (University Research Fellowship), Winton programme for the Physics of SustainabilityThis is the author accepted manuscript. The final version is available from the American Physical Society via http://dx.doi.org/10.1103/PhysRevA.92.06384

Eliminating irreproducibility in SERS substrates

Irreproducibility in surface-enhanced Raman spectroscopy (SERS) due to variability among substrates is a source of recurrent debate within the field. It is regarded as a major hurdle towards the widespread adoption of SERS as a sensing platform. Most of the literature focused on developing substrates for various applications considers reproducibility of lower importance. Here, we address and analyse the sources of this irreproducibility in order to show how these can be minimised. We apply our findings to a simple substrate demonstrating reproducible SERS measurements with relative standard deviations well below 1% between different batches and days. Identifying the sources of irreproducibility and understanding how to reduce these can aid in the transition of SERS from the lab to real world applications.Isaac Newton Trust Leverhulme Trust Winton Programme for the Physics of Sustainability Trinity College, University of Cambridg