Eric Sembrat's Test Bonanza

Quantum optomechanics has attracted increasing attention in recent years due to its broad applications. In 2008, we started a pioneering experiment to trap and cool a glass microsphere in vacuum towards the quantum ground state of an optical tweezer, and to create a quantum-limited microscopic detector. This novel system eliminates the physical contact inherent to clamped cantilevers and can allow ground-state cooling from room temperature. Moreover, the optical trap can be switched off, allowing a particle to undergo free-fall in vacuum after cooling. This system is ideal for studying macroscopic quantum mechanics, gravity induced quantum effects, and creating an ultrasensitive detector with force sensitivity on the order of 10-22 N/Hz1/2.
We have optically trapped glass microspheres in air and vacuum, built an ultrasensitive detector to monitor their Brownian motion, and performed feedback cooling. With a glass microsphere levitated in air, we measured the instantaneous velocity of a Brownian particle, a task that was said to be impossible by Albert Einstein in 1907. Our results provide direct verification of the energy equipartition theorem and the Maxwell-Boltzmann velocity distribution for a Brownian particle. This result was published in Science, and has been included in undergraduate curricula. In vacuum, we have used active feedback to cool the center-of-mass motion of a trapped microsphere from room temperature to a minimum temperature of 1.5 mK, which is an important step towards creating large Schrödinger’s cat states of massive objects.
Unlike conventional optomechanical systems such as clamped cantilevers, microspheres levitated in vacuum may rotate freely. It is interesting to ask how the rotation of a system consisting of millions of strongly interacting atoms may behave nonclassically. This line of thought led us to propose an experimental scheme to create space-time crystals of trapped ions by confining a large number of identical ions in a ring trap with a static magnetic field. We are currently working on this experiment.

Attosecond pulses obtained through high harmonic generation have become a very important tool to study ultrafast phenomena in atoms, molecules, solids and nano-structures. Attosecond technologies required for the characterization of the attosecond pulses and the laser field have been greatly developed for the last decade. However, the conventional attosecond metrologies rely on the photoelectric effect which is slow and complicated, thus limiting applicable areas. In this talk, I discuss three all-optical techniques that can be used for the study of the ultrafast phenomena in attosecond science: Arbitrary optical waveform measurement [1], Space-time measurement of attosecond pulses [2], and Generation of multiple isolated attosecond pulses [3]. All-optical approaches offer very compact, efficient and fast ways to measure and control the ultrafast processes. It exploits the highly non-linear generation process of attosecond pulse generation. I expect other nonlinear interactions in nano-structures hold the prospect of attosecond gating, which would pave the way for attosecond electronic devices [2].

[1] K. T. Kim et al., “Manipulation of quantum paths for space-time characterization of attosecond pulses”, Nature Physics 9, 159–163 (2013).

[2] K. T. Kim et al., “Petahertz optical oscilloscope”, Nature Photonics 7, 958-962 (2013).

[3] K. T. Kim et al., “Photonic streaking of attosecond pulse trains”, Nature Photonics 7, 651–656 (2013).

This talk is devoted to quasi-periodic Schrödinger operators beyond the Almost Mathieu, with more general potentials and interactions. The  links
between the spectral properties of these operators and the dynamical properties of the associated quasi-periodic linear skew-products rule the
game. In particular, we present a Thouless formula  and some consequences of Aubry duality.

Please note this is a WEBINAR

In this talk, I will report on a wide array of findings obtained through our real-time, remote-sensing, non-invasive, text-based `hedonometer'---an instrument for measuring positivity in written expression, now housed online at hedonometer.org. I will show how we have improved our methods to allow us to robustly explore collective, dynamical patterns of happiness and other emotions found in massive text corpora including the global social network Twitter, song lyrics, blogs, political speeches, and news sources.  From the viewpoint of Twitter, I will report on global levels of temporal, spatial (cities and states), demographic, and social variations in happiness and information levels, as well as evidence of emotional synchrony and contagion, and how happiness changes with movement patterns.  Where possible, I will demonstrate that our real-time measure agrees well with various other metrics. I will also discuss how word usage in tweets connects with other features such as food consumption and state-level obesity rates, and can be used to uncover stories in social media. Finally, I will present evidence for how 10 diverse natural languages appear to contain a striking frequency-independent positive bias, describing how this phenomenon plays a key role in our instrument's performance, and how it more deeply reflects human nature.

Electrons in free space have a well-defined mass. Recently, a new class of materials called topological insulators were discovered, where the low energy electrons have zero mass. In fact, these electrons can be described by the same massless Dirac equation that is used to describe relativistic particles travelling close to the speed of light. In this talk I will describe our recent experimental and theoretical investigations of Topological Crystalline Insulators (TCIs) [1]. TCIs belong to the newest category of topological materials [2,3] where topology and crystal symmetry intertwine to create linearly dispersing Fermions similar to graphene. To study this material we use a scanning tunneling microscope. With the help of our high-resolution data, I will show how zero-mass electrons and massive electrons can coexist in the same material. I will discuss the conditions to obtain these zero mass electrons as well the method to impart a controllable mass to the particles and show how our studies create a path to engineering the Dirac band gap and realizing interaction-driven topological quantum phenomena in TCIs.

 [1]  Y. Okada, et.al , Observation of Dirac node formation and mass acquisition in a topological crystalline insulator, Science 341, 1496-1499 (2013)

[2]  L. Fu, Topological Crystalline Insulators. Phys. Rev. Lett. 106, 106802 (2011)

[3]  T. H. Hsieh et al., Topological crystalline insulators in the SnTe material class. Nat.Commun. 3, 982 (2012)

New Roman","serif";
mso-fareast-font-family:"Times New Roman"">I will discuss basic physics phenomena that arise in the processing and design of chocolate products. I will then use these ideas as a springboard to describe some of our “latest” experiments  with soft materials, especially research that pertains to Roman","serif"">creation of novel phases and phase transformations of particles suspended in water. 

The Global Engineering and Research (GEAR) Lab marries mechanical design theory and user-centered product design to create simple, elegant technological solutions for highly constrained environments. This presentation will focus on three GEAR Lab projects that use biologically inspired mechanical systems for this aim. RoboClam is a novel subsea burrowing robot based on the digging mechanisms of razor clams. RoboClam and razor clams use motions of their valves to locally fail and fluidize surrounding substrate to reduce drag and make burrowing energy scale linearly with depth, rather than depth squared for moving through static soil. For engineers, RoboClam technology offers an efficient, mechanically simple, and self-contained burrowing method that has value to applications in anchoring, subsea cable installation, and oil production. The focus of the All-Terrain Knee (ATKnee) project is to create a low-cost, high-performance prosthetic knee that uses only passive mechanical elements to generate a normal walking gait. Ideal gait kinematics of above-knee amputees were used to codify how leg segment mass affects desired knee torque and hip energy. These results were used to optimize a single linear spring and two friction dampers that can replicate the correct knee torque profile to R^2 = 0.90. Our aim is to provide similar levels of performance as $50,000 actively-controlled knees for $100 and create a high-performance, low-cost product appropriate for developing and developed countries. The final project that will be presented focuses on creating off-grid, low-cost drip irrigation systems. Drip irrigation requires up to 60% less water than conventional irrigation methods and is an effective means of helping subsistence farmers grow more and higher value crops to rise out of poverty. We are developing drip emitters that operate at one-tenth the pressure of existing systems in order to lower pumping power and make solar-powered drip irrigation economically viable for poor farmers. This technology uses compliant tubing to maintain a constant flow rate with variations in pressure, a phenomenon inspired by bronchi in human lungs.

Bio:
Amos Winter is the Robert N. Noyce Career Development Assistant Professor in the Department of Mechanical Engineering at MIT. He earned a BS from Tufts University (2003) and an MS (2005) and PhD (2011) from MIT, all in Mechanical Engineering. Prof. Winter’s research focuses on the marriage of mechanical design theory and user-centered product design to create simple, elegant technological solutions for use in highly constrained environments. His work includes design for emerging markets and developing countries, agricultural equipment, irrigation systems, assistive devices, water purification, and subsea systems. Prof. Winter is the principal inventor of the Leveraged Freedom Chair (LFC), an all-terrain wheelchair designed for developing countries that was a winner of a 2010 R&D 100 award and was named one of the Wall Street Journal’s top innovations in 2011. He was the recipient of the 2010 Tufts University Young Alumni Distinguished Achievement Award, the 2010 MIT School of Engineering Graduate Student Extraordinary Teaching and Mentoring Award, the 2012 ASME/Pi Tau Sigma Gold Medal, and was named one of the MIT Technology Review’s 35 Innovators Under 35 (TR35) for 2013. 

Driving nanomagnets by spin-polarized currents offers exciting prospects in magnetoelectronics, but the response of the magnet to such currents
remains poorly understood. For a single domain ferromagnet, I will show that an averaged equation describing the diffusion of energy on a
graph captures the low-damping dynamics of these systems. In particular, I compute the mean times of thermally assisted magnetization reversals
in the finite temperature system, giving explicit expressions for the effective energy barriers conjectured to exist. I will then outline the problem of extending the analysis to spatially non-uniform magnets, leading to a transition state theory for infinite dimensional Hamiltonian
systems.

Over the past decade we have come to appreciate that essentially every giant galaxy, including our own Milky Way, harbors a supermassive black hole at its center.  These monster black holes, with masses of millions or even billions of times the mass of the Sun, play an important role in the evolution of galaxies and the appearance of the observable Universe.  However, unlike stellar-mass black holes that result from the collapse of massive stars at the end of their lives, the origin of supermassive black holes is largely unknown. While direct observations of the first "seeds" of supermassive black holes in the infant Universe are unobtainable with current telescopes, finding and studying the smallest "dwarf" galaxies hosting supermassive black holes today can provide valuable constraints on the masses, host galaxies, and formation mechanism of supermassive black hole seeds.  Until recently, however, very few dwarf galaxies were known to host supermassive black holes.  I will present my recent achievements in this field including the first discovery of supermassive black hole in a dwarf starburst galaxy that resembles those in the earlier Universe, as well as the detection of more than 100 dwarf galaxies exhibiting signatures of actively accreting supermassive black holes.  I will also discuss my on-going and future efforts to study dwarf galaxies and help constrain theories for the origin of supermassive black holes.