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“ If I were again beginning my studies, I would follow the advice of Plato and start with mathematics. ”
- Galileo Galilei
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Physics Conference Room, SB B326
Coffee starts at 12:00 PM and talk starts at 12:15 PM
Jul '18
Sylvain Gigan  -  Wednesday, July 25, 2018
Optical wave propagation in complex media: from pulse shaping to an invariance of the path length
Sorbonne Université Kastler-Brossel Laboratory, Collège de France
ABSTRACT: Scattering of light in heterogeneous media, for instance the skin or a glass of milk, is usually considered an inevitable perturbation or even a nuisance. Through repeated scattering and interferences, this phenomenon seemingly destroys both the spatial and the phase information of any laser illumination. At the spatial level, it gives rise to the well-known “speckle” interference patterns. At the temporal (or spectral) level, a short pulse entering a scattering medium will see its length greatly extended due to the multiplicity of possible path length light can take before exiting the medium. From an operative point of view, scattering greatly limits the possibility to image or manipulate an object with light through or in a scattering medium. Multiple scattering is nonetheless an invaluable field of research for experimentalists and theoreticians alike, at the crossing of optics, condensed matter physics, statistical physics, chaos, to name just a few. 

Multiple scattering is a highly complex but nonetheless deterministic process: it is therefore reversible, in the absence of absorption. Speckle is coherent, and can be coherently controlled. By « shaping » or « adapting » the incident light, it is in principle possible to control the propagation and overcome the scattering process. I will show our recent results on achieving a complete pulse control (spatial and temporal) by means of wavefront shaping. I will also show the experimental demonstration of a peculiar property of light in disorder, namely that the mean path length is independent of the disorder strength. 
Aug '18
Silas Hoffman  -  Friday, August 31, 2018
ABSTRACT: Spin superfluids enable long-distance spin transport through classical ferromagnets by developing topologically protected defects in the magnetic texture. For small spins, in which the magnetization takes quantized values, the topological protection suffers from strong quantum fluctuations. We study the remanence of spin superfluidity inherited from the classical magnet by considering the two-terminal spin transport through a finite spin-1/2 ferromagnetic chain with planar exchange. In the absence of anisotropy in the exchange or an applied magnetic field, the spectrum is gapless. There exist zero-energy domain-wall modes that rotate within the plane of the exchange interaction and are the analogue of the topological defects found in classical magnets. If the system is ordered by an exchange anisotropy, the spectrum is gapped and there exist zero-energy modes localized to the ends of the ferromagnetic chain which are guaranteed by topological properties of the bulk spectrum. We find zero-energy domain-walls, polarized perpendicular to the anisotropy, incident on an ordered chain are reflected as domain-walls polarized in the opposite direction. Furthermore, a domain-wall polarized within the plane of the exchange can be ballistically transmitted through the same magnetic chain of a resonant length. This resonant length depends linearly on the applied magnetic field so that, for a fixed length of chain, the transmission of domain-walls can be tuned by the magnetic field.
Sep '18
Misha Sumetsky  -  Monday, September 17, 2018
Localization of light in an optical microcapillary induced by a droplet
Aston University, Institute of Photonic Technologies
ABSTRACT: We show experimentally and theoretically that whispering gallery modes in a silica microcapillary can be fully localized (rather than perturbed) by evanescent coupling to a water droplet and, thus, form a high-quality-factor microresonator. The spectra of this resonator, measured with a microfiber translated along the capillary, present a hierarchy of resonances that allow us to determine the size of the droplet and variation of its length due to the evaporation. The discovered phenomenon of complete localization of light in liquid-filled optical microcapillaries suggests a new type of microfluidic photonic device as well as an ultraprecise method for microfluidic characterization.
Sep '18
Alex Krasnok  -  Monday, September 24, 2018
Novel aspects of light scattering
Advance Science Research Center and Graduate Center, CUNY
ABSTRACT: Scattering of electromagnetic waves lies in the heart of the most experimental techniques in radiophysics, visible and X-ray optics that allow us to investigate the micro- and nanoworld. Recently, a wide spectrum of exceptional scattering effects attainable in carefully engineered structures have been predicted and demonstrated. In my talk, I will present our recent results on novel aspects of light scattering including coherent virtual absorption, coherently enhanced WPT, and strong coupling regime in excitonic systems.
Oct '18
Larry Liebovitch  -  Monday, October 15, 2018
Oct '18
Miriam Rafailovich  -  Monday, October 22, 2018
Nov '18
Nikodem Poplawski  -  Monday, November 12, 2018
ABSTRACT: The conservation law for the total (orbital plus spin) angular momentum of a Dirac particle in the presence of gravity requires that spacetime is not only curved, but also has a nonzero torsion. The coupling between the spin and torsion in the Einstein–Cartan theory of gravity generates gravitational repulsion at extremely high densities, which prevents a singularity in a black hole and may create there a new, closed, baby universe undergoing one or more nonsingular bounces. We show that quantum particle production caused by an extremely high curvature near a bounce creates enormous amounts of matter and can generate a finite period of inflation. Our scenario has only one parameter, does not depend significantly on the initial conditions, does not involve hypothetical scalar fields, avoids eternal inflation, and predicts plateau-like inflation that is supported by the Planck observations of the cosmic microwave background. This scenario suggests that our Universe may have originated from a black hole existing in another universe.
Nov '18
Ivan Corwin  -  Monday, November 26, 2018
A drunk walk in a drunk world
Columbia University
ABSTRACT: We will consider the effect of a space-time random environment of jumping probabilities on a collection of independent random walkers. Surprisingly, the extreme value behavior for these walkers is governed by the Kardar-Parisi-Zhang universality class which arises in random growth models and random matrix theory. No background of any of these subjects will be assumed.
Dec '18
Eleana Makri  -  Monday, December 10, 2018
ABSTRACT: Photonic limiters are protection devices which transmit electromagnetic radiation at low-level incident intensity while blocking high-intensity electromagnetic signals. Passive limiters typically block excessive radiation by means of absorption, which can often cause their destruction due to overheating. We propose the design of a reflective limiter based on resonant transmission through a defect localized mode. The benefit of this design is that it offers protection by reflecting the excessive radiation instead of absorbing it, which reduces overheating problems and results in a device with an extended dynamic range. In this talk, I will present implementations of this idea in band-gap systems in (i) the infrared domain, based on multilayer photonic crystals, and (ii) the microwave domain, based on chiral or CT symmetric coupled resonator waveguide arrays.
Dec '18
Andrea Alù  -  Monday, December 17, 2018
New frontiers for light control and manipulation using metamaterials
Advanced Science Research Center and Graduate Center, CUNY
ABSTRACT: Metamaterials are artificial materials with properties well beyond what offered by nature, providing unprecedented opportunities to tailor and enhance the interaction between waves with materials. In this talk, I discuss our recent research activity in electromagnetics, nano-optics and acoustics, showing how suitably tailored meta-atoms and arrangements of them open exciting venues to manipulate and control waves in unprecedented ways. I will discuss our recent theoretical and experimental results, including metamaterials for scattering suppression, metasurfaces to control wave propagation and radiation, large nonreciprocity without magnetic bias, giant nonlinearities in properly tailored metamaterials and metasurfaces, and active metamaterials. Physical insights into these exotic phenomena, new devices based on these concepts, and their impact on technology will be discussed during the talk.
Feb '19
ABSTRACT: Our life in today’s fast evolving information age is tied to overwhelming technological challenges related to how we capture information on one hand, and, on the other, how we process it. Nonlinear photonic systems are among the growing technologies promising solutions for these challenges by offering paths toward efficient sensing systems for capturing information, and alternative computing platforms for processing it. One example of nonlinear optical processes is half-harmonic generation, which is splitting photons into pairs of photons at half the input frequency that happens in optical parametric oscillators (OPOs) at degeneracy; its intriguing characteristics such as intrinsic phase and frequency locking as well as possibility of generating quantum states of light have opened up unique opportunities for practical and scalable photonic techniques for molecular sensing and non-classical computing.
In this talk, I will overview the concept of half-harmonic generation and present the results of realizing efficient sources of femtosecond frequency combs in the mid-infrared based on it [1]. These coherent broadband sources in the molecular fingerprint region of the optical spectrum enable direct sensing of several molecular species simultaneously; a capability that has potential applications in areas such as analysis of greenhouse gases and medical breath analysis.
Moreover, I will discuss how half-harmonic generation has enabled development of a novel photonic computing platform, namely the optical Ising machine. Various combinatorial optimization problems in biology, medicine, wireless communications, artificial intelligence and social network that are not easily tractable on conventional computers can be mapped to the Ising problem, and hence the optical Ising machine offers a scalable path for tackling these problems. I will overview a sequence of experiments on development of these half-harmonic-generation-based Ising machines, from their first demonstration in 2014 [2], to a recent large-scale realization that can be programmed to arbitrary Ising problems [3], and one-to-one comparisons with the D-Wave quantum annealer. 
I will conclude the talk by presenting our ongoing work on chip-scale implementation of half-harmonic generation and paths toward quantum photonic engineering.
[1] A. Marandi et al., Optica 3 (3), 324-327 (2016).
[2] A. Marandi et al., Nature Photonics 8 (12), 937-942 (2014).
[3] P. McMahon*, A. Marandi* et al., Science 354 (6312), 614-617 (2016)
Feb '19
Leonardo Ranzani  -  Monday, February 25, 2019
ABSTRACT: Parametric amplifiers increase the measurement fidelity of quantum circuits and are crucial to observe quantum phenomena at microwave as well as optical frequencies. The most common implementation of a lumped-element amplifier is a single nonlinear resonator driven on resonance by a strong electromagnetic pump. In this talk I am going to discuss a more general class of parametric devices consisting of multiple resonant modes coupled via parametric drives. By suitably controlling the amplitude and phases of different parametric processes we can effectively implement new system Hamiltonians, that provide different signal processing functions, such as nonreciprocal signal routing and directional amplification. I will also discuss an implementation of a superconducting multimode parametric circuit on a single chip that can be programmed in situ via a set of microwave drives.
Mar '19
Mar '19
Mariangela Lisanti  -  Monday, March 18, 2019
Princeton University
Mar '19
Evgenii Narimanov  -  Monday, March 25, 2019
Purdue University
Apr '19
Amir Arbabi  -  Monday, April 1, 2019
ABSTRACT: Miniaturized optical systems with planar form factors and low power consumption have many applications in wearable and mobile electronics, health monitoring devices, and as integral parts of medical and industrial equipment. Flat optical devices based on dielectric metasurfaces introduce a new approach for realization of such systems at low cost using conventional nanofabrication techniques. In this talk, I will present our work on dielectric metasurfaces that enable precise control of both polarization and phase with large transmission and high spatial resolution. Optical metasurface components such as MEMs tunable lenses, efficient wave plates, and components with novel functionalities will be discussed. I will also introduce a vertical on-chip integration platform enabled by cascading multiple metasurfaces and active optoelectronic components, and present optical systems such as cameras and spectrometers that have been implemented using this platform. This vertical integration scheme introduces a new architecture for the on-chip integration of conventional optical systems, and enables the unprecedented realization of massively parallel optical systems for computation, data storage, and biomedical sensing applications.
Apr '19
Morrel Cohen  -  Monday, April 15, 2019
Rutgers University
Apr '19
Matthew Sfeir  -  Monday, April 29, 2019
Manipulating exciton dynamics for energy conversion applications
Advance Science Research Center and Graduate Center, CUNY
May '19
ABSTRACT: In collaboration with Argonne National Lab (S. Gray, M. Otten, X. Ma), we studied the effects of quantum entanglement in two physical realizations of the excitonic systems: (a) plasmonically coupled quantum dots in an optical cavity and (b) quasi-two-dimensional CdSe/CdS nanoplatelets (NPLs).  Cavity quantum electrodynamics calculations show that upon optical excitation by a femtosecond laser pulse, entanglement of the quantum dot excitons occurs, and the time evolution of the g(2)  pair correlation function of the cavity photons is an indicator of the entanglement. We also show that the degree of entanglement is conserved during the time evolution of the system. Furthermore, if coupling of the photonic cavity and quantum dot modes is large enough, the quantum dot entanglement can be transferred to the cavity modes to increase the overall entanglement lifetime. This latter phenomenon can be viewed as a signature of entangled, long-lived quantum dot exciton-polariton formation. The preservation of total entanglement in the strong coupling limit of the cavity/quantum dot interactions suggests a novel means of entanglement storage and manipulation in high- quality optical cavities. We also find that, due to formation of biexcitons in an NPL and their subsequent decay, the emitted pairs of cavity photons are entangled at temperatures below 20 K. Under favorable conditions the photon pair can be nearly maximally entangled with the relative photon pair population ~0.5. Finally, we discuss possible experiments, in which the NPL generated photon pair entanglement can be observed, as well as potential applications in integrated quantum photonics.
May '19
Ed Boyden  -  Monday, May 13, 2019