Sanli Faez

Topologically Robust Transport of Photons in a Synthetic Gauge Field

Electronic transport is localized in low-dimensional disordered media. The addition of gauge fields to disordered media leads to fundamental changes in the transport properties. We implement a synthetic gauge field for photons using silicon-on-insulator technology. By determining the distribution of transport properties, we confirm that waves are localized in the bulk and localization is suppressed in edge states. Our system provides a new platform for investigating the transport properties of photons in the presence of synthetic gauge fields.

Observation of Multifractality in Anderson Localization of Ultrasound

We report the experimental observation of strong multifractality in wave functions below the Anderson localization transition in open three-dimensional elastic networks. Our results confirm the recently predicted symmetry of the multifractal exponents. We have discovered that the result of multifractal analysis of real data depends on the excitation scheme used in the experiment.

Fast, Label-Free Tracking of Single Viruses and Weakly Scattering Nanoparticles in a Nanofluidic Optical Fiber

High-speed tracking of single particles is a gateway to understanding physical, chemical, and biological processes at the nanoscale. It is also a major experimental challenge, particularly for small, nanometer-scale particles. Although methods such as confocal or fluorescence microscopy offer both high spatial resolution and high signal-to-background ratios, the fluorescence emission lifetime limits the measurement speed, while photobleaching and thermal diffusion limit the duration of measurements. Here we present a tracking method based on elastic light scattering that enables long-duration measurements of nanoparticle dynamics at rates of thousands of frames per second. We contain the particles within a single-mode silica fiber having a subwavelength, nanofluidic channel and illuminate them using the fibers strongly confined optical mode. The diffusing particles in this cylindrical geometry are continuously illuminated inside the collection focal plane. We show that the method can track unlabeled dielectric particles as small as 20 nm as well as individual cowpea chlorotic mottle virus (CCMV) virions-26 nm in size and 4.6 megadaltons in mass-at rates of over 3 kHz for durations of tens of seconds. Our setup is easily incorporated into common optical microscopes and extends their detection range to nanometer-scale particles and macromolecules. The ease-of-use and performance of this technique support its potential for widespread applications in medical diagnostics and micro total analysis systems.

Full characterization of anisotropic diffuse light.

We demonstrate a method for fully characterizing diffuse transport of light in a statistically anisotropic opaque material. Our technique provides a simple means of determining all parameters governing anisotropic diffusion. Anisotropy in the diffusion constant, the mean free path, and the extrapolation length are, for the first time, determined independently. These results show that the anisotropic diffusion model is effective for modeling transport in anisotropic samples, providing that the light is allowed to travel several times the transport mean free path from the source.

Classification of light sources and their interaction with active and passive environments

The emission properties of a molecular light source depend on its optical and chemical environment. This dependence, however, is dierent for various light sources. We present a general classication of sources by introducing the concepts of Constant Amplitude and Constant Power Sources. The unforeseen consequences of this classication are illustrated for photonic studies by random laser experiments. Comparison of the experimental results with properly customized rate equations identies the type of light source in the gain medium and an estimate for its quantum eciency. Our results require a major revision of source studies in multiple scattering media.

Varying the effective refractive index to measure optical transport in random media.

We introduce a new approach for measuring both the effective medium and the transport properties of light propagation in heterogeneous media. Our method utilizes the conceptual equivalence of frequency variation with a change in the effective index of refraction. Experimentally, we measure intensity correlations via spectrally resolved refractive index tuning, controlling the latter via changes in the ambient pressure. Our experimental results perfectly match a generalized transport theory that incorporates the effective medium and predicts a precise value for the diffusion constant. Thus, we directly confirm the applicability of the effective medium concept in strongly scattering materials.

Snapshots of Anderson localization beyond the ensemble average

We study (1+1)D transverse localization of electromagnetic radiation at microwave frequencies directly by two-dimensional spatial scans. Since the longitudinal direction can be mapped onto time, our experiments provide unique snapshots of the build-up of localized waves. The evolution of the wave functions is compared with numerical calculations. Dissipation is shown to have no effect on the occurrence of transverse localization. Oscillations of the wave functions are observed in space and explained in terms of a beating between the eigenstates. PACS numbers: 42.25.Dd, 72.15.Rn, 41.20.Jb 1 ar X iv :1 20 1. 06 35 v1 [ co nd -m at .d is -n n] 3 J an 2 01 2 Recent years witnessed a renaissance in experimental studies on Anderson localization. This phenomenon, conceived by P. W. Anderson in 1958 [1], originally described the absence of diffusion of electrons in random lattices due to interference. Since Anderson localization is in essence a wave phenomenon, physicists have successfully extended the scope of localization studies to electromagnetic waves [2–5], ultrasound [6], and matter waves [7–9]. Similar to other phase transition phenomena, dimensionality plays an important role. For d ≤ 2, all states are localized, whereas for d = 3 a phase transition from diffusive to localized behavior occurs at a critical scattering strength [10]. In the special case of transverse localization, formulated by De Raedt et al. [11], one dimension is designed not to be disordered, whereas disorder is introduced in the other dimension(s). As a consequence, waves spread out in the disorder-free dimension, but are confined in the other dimensions. Waves are always localized in the transverse directions as long as the transverse system length L is larger than the localization length ξ. Effectively, transverse localization reduces the number of spatial coordinates in the system: the coordinate along which the sample is extruded can be seen as the time-axis in the time-dependent Schrödinger equation. Stationary transverse localization experiments could thus provide a unique insight into how a localized wave develops over time. Studying and understanding this intriguing aspect of transverse localization experimentally is the central topic of this paper. Pivotal experiments on weakly scattering disordered photonic lattices [12–14] have focussed on the observation of localized wave functions after a certain fixed propagation distance and the effect of nonlinearity on the transverse localization length. Both theoretical and experimental studies have revealed interesting dynamical properties of the periodically kicked quantum rotator which bears close resemblance to Anderson localization [15, 16], suggesting that studying the dynamics of localization itself is important. The unique property of transverse localization experiments that enables us to map one spatial dimension onto time is ideally suited for this purpose. First, we provide new results on transverse localization by performing experiments with microwaves in 2D. Instead of measuring the intensity at the end of our samples, we study the evolution of the extent of the waves as a function of propagation distance. Second, we compare our experimental results with numerical solutions to a 2D Schrödinger-like equation from which we deduce information regarding the effect of dissipation on localization. Since localization was introduced for classical waves the issue of absorption has been the subject

Polaritonic normal-mode splitting and light localization in a one-dimensional nanoguide

Harald R. Haakh, ∗ Sanli Faez, 2 and Vahid Sandoghdar 3 Max Planck Institute for the Science of Light, Günther-Scharowsky-Straße 1, D-91058 Erlangen, Germany. Present Address: Debye Institute for Nanomaterials Science and Center for Extreme Matter and Emergent Phenomena, Utrecht University, Princetonplein 5, 3584CC, Utrecht, The Netherlands Friedrich Alexander University Erlangen-Nuremberg, D-91058 Erlangen, Germany (Dated: 28 October 2015)

Plasmonics, Tracking and Manipulating, and Living Cells: general discussion

Thorben Cordes, William Moerner, Michel Orrit, Sergey Sekatskii, Sanli Faez, Paola Borri, Himangshu Prabal Goswami, Alex Clark, Patrick El-Khoury, Sandra Mayr, Jacek Mika, Guowei Lyu, Daniel Cross, Francisco Balzarotti, Wolfgang Langbein, Vahid Sandoghdar, Jens Michaelis, Arindam Chowdhury, Alfred J. Meixner, Niek van Hulst, Brahim Lounis, Fernando Stefani, Frank Cichos, Maxime Dahan, Lukas Novotny, Mark Leake and Haw Yang, FRSC

Optical tracing of multiple charges in single-electron devices

Single molecules that exhibit narrow optical transitions at cryogenic temperatures can be used as local electric-field sensors. We derive the single-charge sensitivity of aromatic organic dye molecules, based on quantum mechanical considerations. Through numerical modeling, we demonstrate that by using currently available technologies it is possible to optically detect charging events in a granular network with a sensitivity better than