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Physics Conference Room, SB B326
Coffee starts at 12:00 PM and talk starts at 12:15 PM
- Monday, February 3, 2014
ABSTRACT: Living objects at the nanoscale can be viewed as molecular complexes, whose dynamics is often controlled by the transfer of single charges or single-photon absorption events. In many senses, it is similar to the principles of operation of semiconductor nanostructures and elements of molecular electronics. Correspondingly, the methods of condensed matter and statistical physics can be applied.
In this talk, I address proton-pumping complexes and proton-driven nanomotor of the mitochondria membranes. These systems convert the energy obtained from the food to the proton gradient across the membrane, to the mechanical rotation of the nanomotor, and, finally, to the energy of chemical compounds. We propose simple physical models for these complexes which not only allow the quantitative description but can inspire the implementations in nanoelectronics as well.
In the end of the talk, I discuss some details of electron transfer calculations bridging the Marcus theory and equations of motion, two methods widely used in chemistry and physics, respectively. We demonstrate that as a manifestation of the Goldilocks principle, the optimal transfer is governed by a single parameter which is equal to just the inverse square root of two.
- Monday, February 10, 2014
ABSTRACT: The Discrete Amplification Photon Detection technology enables a unique photodetector, in which a combination of an avalanche and negative-feedback mechanisms produces ultra-sensitive, very high gain, low noise, very small pixel size photodetectors and photodetector arrays. The discrete amplification physical mechanism is not dependent on the ratio of electrons and holes ionization coefficients, thus it can be implemented in several compound semiconductor material systems, such as silicon, GaAs/AlGaAs, and InGaAs/InGaAsP/InP. This talk describes the operation principle of the technology, the advantages and tradeoffs, as well as how this technology compares to, and differs from, other competing high sensitivity approaches. As this technology can detect single photons, single-photon detection and characterization will be described, as well as other low-light level threshold detection methodologies used to characterize the Discrete Amplification photodetectors. Record setting sensitivity results at room temperature detection using 1.5 micron wavelength-sensitive detectors will be presented. In addition, the development status of the technology, development plans and challenges for the two main applications, night vision and ranging, will be described.
- Friday, February 14, 2014
NOTES: Event starts at 4:00 PM on Friday
- Monday, February 24, 2014
- Monday, March 3, 2014
ABSTRACT: Recent progress in femtosecond electronic spectroscopy brought renewed interest in the transfer of electronic excitation energies in large molecular complexes. In particular, there have been speculations that the energy transfer in some photosynthetic light harvesting complexes may involve wave-like coherent quantum dynamics motion rather than the rate behavior. However, to what extent the quantum coherence is detrimental to efficient and robust energy transfer has remained a controversial issue. Advanced level of theories and development of reliable quantum mechanical models are crucial for quantitative resolution of such issue. This talk will present a range of theories developed recently, which can address nonequilibrium effects, quantum coherence, and soft nature of molecular environments for a fairly general class of systems. The talk will also discuss exciton-bath modeling of photosynthetic light harvesting complexes and quantum dynamical calculation of energy transfer dynamics. These results suggest that quantum coherence can play a subtle but significant role in minimizing the negative effects of thermal fluctuations and disorder in order to create both efficient and robust energy transfer dynamics mechanism.
- Monday, March 10, 2014
ABSTRACT: Many of the topological insulators, in their naturally available form are not insulating in the bulk. It has been shown that some of these metallic compounds, become superconductor at low enough temperature and the nature of their superconducting phase is still widely debated. In this talk I show that even the s-wave superconducting phase of doped topological insulators, at low doping, is different from ordinary s-wave superconductors and goes through a topological phase transition to an ordinary s-wave state by increasing the doping. I show that the critical doping is determined using the SU(2) Berry phase on the fermi surface of doped topological insulator and can be modified by different tunable features of the material. At the end I present the results of a recent experiment on the Josephson junctions made of thin films of Bismuth selenide , which can be explained using our theory of doping induced phase transition in topological insulators.
- Monday, March 24, 2014
ABSTRACT: In contrast to embryonic stem cells, adult stem cells are subject to differentially small changes in the mechanical, morphological, and chemical cues. The nature of the response may provide us with a better understanding of the role of stem cells in tissue regeneration, wound healing, and aging. Here we discuss how new materials can be engineered where each of these factors can be varied independently such that their influence on stem cell response can be assessed both individually and collectively.
- Monday, March 31, 2014
ABSTRACT: The first commercial optical communications system was deployed over 30 years ago, since that time new technologies have dramatically enhanced the capabilities of optical networks. The explosive growth of the Internet has been enabled by these technical innovations, and this trend continues. The early simple point-to-point links have been replaced with systems with more than 105 times more capacity per fiber, connected in a sophisticated mesh network. This talk will survey the history of optical communications, with special emphasis on recent innovations that enable the optical layer to be more agile than ever before.
Sheryl Woodward received her Ph.D. degree in Physics from Caltech. For over 25 years she has been in AT&T’s research organization - first with the Crawford Hill Laboratory of Bell Labs Research, and then with AT&T Labs-Research in Middletown, NJ. She has done research on topics ranging from technologies for cable television to optical networking for continental-backbone networks. Her current research focuses on software-defined networking for the wide-area network.
Steve G. Greenbaum
- Monday, April 7, 2014
ABSTRACT: Fundamental materials research is essential to move present-day energy storage technologies to the scale needed to develop all-electric vehicles and to manage intermittent renewable sources such as wind and solar. Comparable advances are also required to develop compact power sources for new medical and military/aerospace applications. Structural studies of materials utilized in lithium battery technology are often hampered by the lack of long-range order found only in well-defined crystalline phases. Powder x-ray diffraction yields only structural parameters that have been averaged over hundreds of lattice sites, and is unable to provide structural information about amorphous compounds. Our laboratory utilizes solid state nuclear magnetic resonance (NMR) methods to investigate structural and chemical aspects of lithium ion cathodes, anodes, electrolytes, interfaces and interphases. NMR is element- (nuclear-) specific and sensitive to small variations in the immediate environment of the ions being probed, for example Li+, and in most cases is a reliably quantitative spectroscopy in that the integrated intensity of a particular spectral component is directly proportional to the number of nuclei in the corresponding material phase. NMR is also a powerful tool for probing ionic and molecular motion in lithium battery electrolytes with a dynamic range spanning some ten orders of magnitude through spin-lattice relaxation and self-diffusion measurements. Brief summaries of several recent NMR investigations will be presented: (i) single crystal studies of LiMPO4 (M = Fe, Co, Ni) lithium ion battery cathodes; (ii) electrode passivation in lithium ion batteries; (iii) charge transfer in hybrid CFx/silver vanadate cathodes for medical devices; (iv) structure and dynamics of disordered fast-ion conducting Li3PS4 electrolytes for Li-S batteries.
- Monday, April 28, 2014
ABSTRACT: One of the major challenges in physics is to understand how the classical behavior of macroscopic objects emerges in a universe whose laws are fundamentally quantum mechanical. The field of optomechanics attempts to address this issue by studying the quantum behavior of devices in which a macroscopic object’s motion is coupled to individual photons. In the past few years, experiments have demonstrated a number of quantum effects in these devices, including ground-state cooling, entanglement, and the quantum back-action of displacement measurements. I will give an overview of our group's work on these topics. I will also designs for substantially improved optomechanical devices that consist entirely of superfluid helium.
- Wednesday, April 30, 2014
ABSTRACT: Dielectric nanostructures makes a new twist on light scattering phenomena. Subwavelength particles made of high-dielectric materials exhibit very strong magentic response in visible range, which has been recently demonstrated experimentally. The lower losses, compared to plasmonic counterparts, allow to employ dielectric nanostructures for a variety of applications spanning from optical nanotantennas towards metamaterials. We experimentally demonstrated the suppression of the backward scattering and enhancement of the forward scattering due to superposition of the electric and magnetic dipole excitations of a single element. Moreover, due to othognality of optically induced diplole modes, the scattering pattern is polarization independent. It results in azimuthally symmetric unidirectional scattering which can be achieved even for a single element. Furthermore, directionality can be further enhanced by forming a chain of such elements. Although there is a tradeoff between energy confinement and directionality for different inter-particle distances, the properties of vanishing backward scattering and azimuthal symmetry are always preserved even for random ensembles of such elements. It makes them the perfect candidates for compact low loss optical nanoatennas.
- Monday, May 5, 2014
ABSTRACT: Intersubband transitions in n-doped semiconductor heterostructures provide the possibility to quantum engineer one of the largest known nonlinear optical responses in condensed matter systems. I will discuss how we engineer and use these nonlinearities to produce room-temperature terahertz quantum cascade laser sources based on efficient intra-cavity difference-frequency mixing, polaritonic metasurfaces with ultra-fast electrical tuning, and ultra-thin highly-nonlinear metasurfaces for frequency conversion. Structures discussed here represent a novel kind of hybrid metal-semiconductor metamaterials in which exotic optical properties are produced by coupling electromagnetically-engineered resonances in plasmonic nanostructures with quantum-engineered intersubband transitions in semiconductor heterostructures.
- Wednesday, May 7, 2014
The free will theorem
Gorenstein Professor of Mathematics, Queens College (Emeritus, Princeton University)
ABSTRACT: The limited degree of free will required to make a binary decision independent of previous history is also inherent in elementary particles. The proof relies on three uncontested axioms taken from quantum mechanics and relativity theory.
- Monday, June 23, 2014
ABSTRACT: The paint layers of art objects are extremely complex systems, but there are many reasons to improve our ability to characterize them. More sensitive detection of pigments and dyes can provide valuable insights into vanished cultures, and help ensure that proper conservation techniques are applied. A better understanding of protein conformation and fat migration in dried paint layers would shed much-needed light on artistic practices and potential degradation processes. I will give a brief overview of the field and then discuss some current areas of interest in the study of paint layers, with a focus on established and novel applications of surface-enhanced Raman techniques for the identification of colorants.
NOTES: Room SB C201, starts at 11 am
- Monday, September 8, 2014
ABSTRACT: Quantum optics arose with the invention of the laser. Early work focussed on developing a quantum theory of the laser and on better understanding the nature of the quantized electromagnetic field. It was for this latter work that Roy Glauber won the 2005 Nobel Prize in Physics. The fields produced by nonlinear optical devices also received attention, because of their unusual correlation properties. In the 1980's two major areas of study were quantum metrology, using nonclassical states of the electromagnetic field to improve the accuracy of measurements, and micromasers and microlasers, optical devices that are pumped by a single atom at a time. In the 1990's the field split into three parts. Some researchers turned their attention to the study of Bose-Einstein condensates and related phenomena in matter-wave physics. Another group pursued the newly emerging field of quantum information, while a third continued with work on mainstream quantum optics. Today all of these efforts are alive and doing very well, and they have been joined more recently by the study of quantum opto-mechanics. A broad overview of these trends will be presented as well as more detailed discussions of some selected topics.
- Monday, September 22, 2014
ABSTRACT: Coherent backscattering, also known as weak localization, is one of the most striking examples of the subtle interplay between interference and disorder in scattering samples. Due to constructive interference between time-reversed paths inside the sample, the backscattered intensity exhibits a peak exactly at the direction opposite to the incident wave. Recently we have discovered an analogue of coherent back scattering in multimode optical fibers with strong mode mixing. I will discuss how fibers provide new opportunities to directly access and control the relative phase between the time-reversed paths, allowing us to flip the backscattered peak, and turn it into a dip. I will then show how we utilize correlations between the time-reversed paths for secure optical key distribution.
- Monday, September 29, 2014
ABSTRACT: I review such aspects of low-D physics as quantum number fractionalization, non-Fermi liquid behavior, and spontaneous mass generation.
- Monday, October 6, 2014
ABSTRACT: We will discuss the role of symmetries in three different areas of large scale structure: 1. how to test the equivalence principle using black holes in centers of galaxies; 2. how to measure gravitational redshift on cosmological scales using parity-violating signatures in correlation functions; 3. how spontaneously broken symmetries give us non-perturbative relations between different correlation functions.
- Monday, October 20, 2014
ABSTRACT: Advances in X-ray astronomy open the possibility for high precision spin and mass determination for astrophysical black holes starting the era of precision black hole physics. These observations turn astrophysical black holes into sensitive probes of ultra-light axion-like particles motivated by the strong CP problem and string theory.
When the axion Compton wavelength matches the black hole size, the axions develop "superradiant" atomic bound states around the black hole "nucleus" through the Penrose superradiance process. Their occupation number grows exponentially by extracting rotational energy from the ergosphere, culminating in a rotating Bose-Einstein axion condensate emitting gravitational waves. This transfer of angular momentum from the black hole to the axion condensate results in mass gaps in the spectrum of rapidly rotating black holes and gives rise to distinctive gravity wave signals.
Lea Ferreira dos Santos
- Monday, October 27, 2014
ABSTRACT: We consider one-dimensional isolated interacting quantum systems that are taken out of equilibrium instantaneously. Three aspects are addressed: (i) the relaxation process, (ii) the size of the temporal fluctuations after relaxation, (iii) the conditions to reach thermal equilibrium. The relaxation process and the size of the fluctuations depend on the interplay between the initial state and the Hamiltonian after the perturbation, rather than on the regime of the system. They may be very similar for both chaotic and integrable systems. The general picture associating chaos with the onset of thermalization is also further elaborated. It is argued that thermalization may not occur in the chaotic regime if the energy of the initial state is close to the edges of the spectrum, and it may occur in integrable systems provided the initial state is sufficiently delocalized.
- Monday, November 3, 2014
ABSTRACT: Proton exchange membrane fuel cells (PEMFC) have attracted great attention because of their high power density, low operation temperature ] and almost pollution-free emission . In fuel cells power is generated via the conduction of H+ ions through a polyelectrolyte membrane, commonly composed of sulfonated tetrafluoroethylene based fluoropolymer-copolymer. The function of the fuel cell constitutes a balance between hydrogen oxidation and oxygen reduction reactions where Pt nanoparticles are used to catalyze the reactions at the electrodes . Although the hydrogen oxidation process is a fast electrochemical reaction, challenges come up when impure hydrogen is used. Carbon monoxide is well known to poison the catalyst by blocking active sites on the catalyst’s surface , which prevents the hydrogen adsorption and subsequent oxidation propane, or alcohols can be an inexpensive alternative to pure hydrogen gas, but the high CO and CO2 content of reformed gas, even after purification, poses a major drawback. Hence the ability to engineer a CO resistant system would be a critical step towards enabling the commercialization of a competitively priced hydrogen fuel cell. We have developed a technique whereby Au particle nanoplatelets, 3nm in diameter, and only three atomic layers thick, could be reproducibly formed at the air water interface, and then coated onto any arbitrary surface simply by using the LB technique. Here we show that when this layer of NP is deposited directly onto the membrane of a PEM fuel cell, the efficiency of the cell running in ambient conditions is enhanced by more than 80% and an H2 stream with as much as 20% CO2 is tolerated. DFT calculations indicate that a two-step oxidation process is also present in this case, which enables the oxidation reaction to take place in a broad temperature range, extending well below ambient.
- Monday, November 17, 2014
ABSTRACT: The development of collective long-range order by means of phase transitions occurs by the spontaneous breaking of fundamental symmetries. Magnetism is a consequence of broken time-reversal symmetry, whereas superfluidity results from broken gauge invariance. The broken symmetry that develops below 17.5 kelvin in the heavy-fermion compound URu2Si2 has long eluded such identification. Here we show that the recent observations of Ising quasiparticles in URu2Si2 results from a spinor order parameter that breaks double time-reversal invariance, mixing states of integer and half-integer spin. Such "hastatic" order hybridizes uranium-atom conduction electrons with Ising 5f2 states to produce Ising quasiparticles; it accounts for the large entropy of condensation and the magnetic anomaly observed in torque magnetometry. Hastatic order predicts a tiny transverse moment in the conduction-electron sea, a collosal Ising anisotropy in the nonlinear susceptibility anomaly and a resonant, energy-depedent nematicity in the tunnelling density of states. We also discuss the microscopic origin of hastatic order, identifying it as a fractionalization of three-body body bound-states into integer spin fermions and half-integer spin bosons.
Work done with Piers Coleman and Rebecca Flint.
References: PC, P. Coleman and R. Flint Nature 493, 421 (2013)
- Monday, November 24, 2014
ABSTRACT: Metamaterials with properties that vary from point to point in space and time are suitable for new applications such as an “optical cloak”. Colloidal dispersions of metal nano-rods in dielectric fluids are appropriate to construct such spatially varying and electrically reconfigurable optical metamaterials. An applied electric field can be used to control the orientation and concentration of nano-rods, and thus modulate the optical properties of the dispersion. For example, by using gold nano-rods dispersed in toluene, we demonstrate an electrically induced change in refractive index on the order of 0.1 which was used to change the visibility of metal object. This approach is also valid to design an omnidirectional broadband optical “black-hole”.
- Monday, December 8, 2014