## Events - Weekly

**March 2013 >>**

Sunday,
March 24 |
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Monday,
March 25 |

Biophysics Seminar - Roman Stocker (MIT) "Spying on the lives of marine microbes: From biophysics to ecology " At a time when microbial ecology is largely traveling along genomic roads, we cannot forget that the functions and services of microbes depend greatly on their behaviors, encounters, and interactions with their environment. New technologies, including microfluidics and high-speed video microscopy, provide a powerful opportunity to spy on the lives of microbes, directly observing their behaviors at the spatiotemporal resolution most relevant to their ecology, and enabling a deeper understanding of the biophysical mechanisms underpinning these behaviors. I will illustrate this 'quantitative natural history approach' to microbial ecology by focusing on marine bacteria, unveiling striking adaptations in their motility and chemotaxis and describing how these are connected to their incredibly dynamic, gradient-rich microenvironments. Specifically, I will present (i) sub-micrometer imaging of single cells at up to thousand frames per second, demonstrating that marine bacteria have a unique mode of swimming, exploiting a mechanical buckling instability of their flagellum to reorient; and (ii) microfluidic experiments that capture the dramatic chemotactic abilities of marine bacteria, including bacterial pathogens storming towards the roiling surface of their coral hosts. Through these examples, I aim to illustrate how we can use direct visualization to learn about the biophysical mechanisms and the ecological implications of the behaviors of the smallest of life forms. Joseph Henry Room · 12:00 p.m.– 1:00 p.m.Harnessing the Atom-like Properties of Single Spins in Diamond - Lee C. Bassett, Center for Spintronics and Quantum Computation, University of Califor The past decade has seen remarkable progress in the isolation and control of single spins in solid state devices. With electron spin coherence times in some materials now measured in seconds, single spins provide many features formerly unique to atomic systems in a form amenable to engineering complex integrated devices through semiconductor nanofabrication. In particular, the nitrogen-vacancy (NV) center in diamond has emerged as a promising single-spin system for wide-ranging applications in quantum computing, quantum communication, and nanoscale sensing. The NV center’s electronic spin can be initialized and measured optically, has millisecond coherence times at room temperature, and it provides access to individual nuclear spins with even better coherence properties. Recently, we have developed several techniques to control the NV center’s spin using coherent light-matter interactions – protocols that can be used to access other spin systems that lack the NV center’s unique optical addressability but might offer desirable properties for other applications. I will review the current state of this exciting field, describe several of our recent experiments, and outline the challenges and possibilities for the road ahead. Jadwin A07 · 12:15 p.m.– 1:15 p.m.Condensed Matter Seminar - Andrew Sachrajda, The National Research Council - Coherent Behaviour in a Triple Quantum Dot Circuit In this talk I will describe our experimental investigations of an AlGaAs/GaAs based triple quantum dot circuit and their comparison with theoretical models. We are able to employ both quantum transport and charge detection down to single electron/spin occupation and employ many of the pulsing techniques developed previously for two dot circuits. Our particular focus is the (1,1,1) regime in which a single spin occupies each quantum dot. By varying pulse parameters we are able to observe coherent behaviour between specific three-spin levels including the DiVincenzo all-exchange qubit and various manifestations of Landau-Zener -Stückelberg oscillations and their interplay. I will demonstrate the triple quantum dot equivalent of the double quantum dot Pauli blockade effect and show how in a linear triple quantum dot leakage currents can occur directly between edge dots via coherent quantum superpositions where the occupation of the center dot remains fixed. Finally I will demonstrate a quantum backaction process mediated via single phonon interferometry. The figure below shows experimental LZS oscillations and the device layout used. PCTS Seminar Room · 1:15 p.m.– 2:30 p.m.High Energy Theory Seminar - Costis Papayeorgakis, Rutgers University - "On the (2,0) theory and 5D SYM" "We will review the connection between the six-dimensional (2,0) theory and maximally supersymmetric Yang-Mills in five dimensions (MSYM). We will discuss the implications of a conjectured relation between the two, at all energy scales, for MSYM. We will also deconstruct MSYM from a four-dimensional circular quiver gauge theory and consider the possibility of instanton-solitons contributing to perturbative amplitudes." PCTS Seminar Room · 2:30 p.m.– 3:30 p.m. |

Tuesday,
March 26 |

From molecules to development: revealing simple rules of biological clocks - Qiong Yang, Stanford University Organisms from cyanobacteria through vertebrates make use of biochemical and genetic oscillators to drive repetitive processes like cell cycle progression and vertebrate somitogenesis. Oscillators also allow organisms to anticipate natural environmental rhythms, as exemplified by the circadian clock. Despite the complexity and variety of biological oscillators, their core design is thought to be shared. Notably, they all possess an essential negative feedback loop. However, absent crucial elements negative feedback circuits often settle into a stable steady state rather than oscillating. In this talk, I first discuss computationally how several modifications of the basic activator/repressor circuit can promote oscillation. Then I ask which of these strategies are actually utilized in the complex biological oscillator circuits found in nature by dissecting a mitotic oscillator in the Xenopus laevis early embryos. I found that the core negative feedback system of Cdk1-APC/CCdc20 operates as a time-delayed, digital switch, with a time lag of ~15 min between the activation of Cdk1 and its repressor APC/CCdc20 and a tremendously high degree of ultrasensitivity. Mathematical modeling indicates that this time delay must be coupled to the ultrasensitivity to ensure robust oscillations and segregation of cell-cycle phases. Principles uncovered here may also apply to other activator-repressor oscillators and help in designing robust synthetic clocks. Joseph Henry Room · 1:30 p.m.– 6:00 p.m.High Energy Theory Informal Seminar - IAS - Tomasz Taylor, Northeastern U. - Superstring Amplitudes as a Mellin Transform of Supergravity At the tree level, the maximally helicity violating amplitudes of N gauge bosons in open superstring theoryand of N gravitons in supergravity are known to have simple representations in terms of tree graphs.For superstrings, the graphs encode integral representations of certain generalized hypergeometric functions of kinematic invariants while for supergravity, they represent specific kinematic expressions constructed from spinor-helicity variables. We establish asuperstring/supergravity correspondence for this class of amplitudes, by constructing a mapping between thepositions of gauge boson vertices at the disk boundary and the helicity spinors associated to gravitons. After replacing vertex positions by a larger set ofN(N-3)/2 coordinates, the superstring amplitudes become (multiple) Mellin transforms of supergravity amplitudes, from the projective space into the dual Mellin space of N(N-3)/2 kinematic invariants. We elaborate on the properties of Mellin and inverse Mellin transformsin the framework of superstring/supergravity correspondence. Bloomberg Lecture Hall - Institute for Advanced Study · 1:30 p.m.– 2:30 p.m. |

Wednesday,
March 27 |

Thursday,
March 28 |

High Energy Theory Discussion Seminar - IAS - Graham Kribs, University of Oregon & IAS - Particle Physics post-Moriond: A Discussion Bloomberg Lecture Hall - Institute for Advanced Study · 10:00 a.m.–11:00 a.m.High Energy Physics Seminar- Michelle Dolinski-Drexel University- "Neutrinoless Double Beta Decay with EXO and Beyond." Neutrino masses provide a direct window into Physics Beyond the Standard Model. It is an open question whether massive neutrinos are Majorana fermions or Dirac fermions. Majorana neutrinos, which violate lepton number conservation, offer an intriguing mechanism for generating small neutrino masses. The most practical experimental approach for discovering Majorana neutrinos is the search for neutrinoless double beta decay. I will present the current results of the EXO-200 experiment, a large liquid xenon detector which is searching for the neutrinoless double beta decay of Xe-136. I will also discuss innovations by the EXO Collaboration and others that will be needed for the next generation of planned detectors and beyond. Jadwin A09 · 3:00 p.m.– 4:00 p.m.Hamilton Colloquium Series - Alain Aspect, Institut d'Optique, Palaiseau - "From Einstein's intuition to quantum bits: a new quantum age?" In 1935, with co-authors Podolsky and Rosen, Einstein discovered a weird quantum situation, where particles in a pair are so strongly correlated that Schrödinger called them “entangled.” By analyzing that situation, Einstein concluded that the quantum formalism was incomplete. Niels Bohr immediately opposed that conclusion, and the debate lasted until the death of these two giants of physics. In 1964, John Bell produced the famous inequalities that have allowed experimentalists to settle the debate, and to show directly that the revolutionary concept of entanglement is indeed a reality. Based on that concept, a new field of research has emerged, quantum information, where one uses quantum bits, the so-called “qubits.” In contrast to classical bits, which are either in state 0 or state 1, qubits can be simultaneously in state 0 and state 1. Entanglement between qubits enables conceptually new methods for processing and transmitting information. Large scale practical implementation of such concepts might revolutionize our society, as did the laser, the transistor and integrated circuits, some of the most striking fruits of the first quantum revolution, which began with the 20th century. Jadwin A10 · 4:30 p.m.– 5:30 p.m. |

Friday,
March 29 |

Saturday,
March 30 |