Quantum Sciences Seminar Series - Jérémie Viennot, ENS Paris, "Out of equilibrium charge dynamics in a cQED architecture"
Mar 11, 2014 · 1:00 p.m.– 2:00 p.m. · Jadwin 111
In the context of circuit quantum electrodynamics, recent developments made it possible to build hybrid circuits , including many types of quantum dots. The versatility of these systems allows us to explore several directions, from quantum information engineering to many-body physics, all in a circuit QED architecture. I will present some of the experiments of our group where a carbon nanotube-based double quantum dot is coupled to a microwave cavity.
Using a novel carbon nanotube stamping technique , we demonstrate a strong electron confinement, allowing us to bring the system at resonance with the cavity and use it as a charge qubit. We characterise the response of this circuit out of equilibrium, driving the system either with a finite bias or with a microwave spectroscopic tone .
Combined with exchange Zeeman fields induced by ferromagnetic interfaces, such a control should enable us to go towards spin-photon coupling and spin qubit experiments for circuit QED . I will discuss some preliminary results pointing towards spin-photon coupling signatures in such an architecture.
 M.R. Delbecq et al. Nature Comm., 4, 1400 (2013).
 J.J. Viennot et al., submitted.
 J.J. Viennot et al., arXiv:1310.4363.
 A. Cottet et al., Phys. Rev. Lett. 105, 160502 (2010).
Mar 11, 2014 · 2:00 p.m.– 3:00 p.m. · Joseph Henry Room
Neutron stars and quark stars are not only characterized by their mass and radius, but also by how fast they spin, through their moment of inertia, and how much they can be deformed, through their Love number and quadrupole moment. These depend sensitively on the star's internal structure, and thus on unknown nuclear physics. In spite of this, we have found quasi-universal (I-Love-Q) relations between the moment of inertia, the Love number and the quadrupole moment that are independent of the neutron star's and quark star's internal structure.
We have used these as a basis of a no-hair-like theorem for neutron stars that bares strong similarities with the well-known black hole no-hair theorems. These relations can be used to learn about neutron star deformability through observations of the moment of inertia, break degeneracies in gravitational wave detection to measure spin in binary inspirals, and test General Relativity in a nuclear-structure independent fashion.
Mar 12, 2014 · 2:00 p.m.– 3:00 p.m. · Jadwin A06
Physical forces can induce long-ranged interactions and thus propagate information on large scales. Especially during the development of an organism, coordination on large scales in short time is essential. My aim is to discover the principal mechanisms of how physical forces induce, transmit and respond to biological signals and thus orchestrate development and shape morphology.
The network-forming slime mold Physarum polycephalum lacks any central coordination center, yet it shows often-termed intelligent dynamics in the way it grows and adapts its network morphology. My work investigates the role of fluid mechanics for transport and signal transfer during the morphological dynamics of this network-like slime mold. I combine experimental observations of the fluid flow and its driving force with the development of the theoretical concept of transport by peristaltic flow in a network. This synergy allows me to show that the slime mold actively controls its internal fluid flow by establishing a peristaltic wave. This peristaltic wave always spans the total extent of an individual independent of its size. Thus, I find that the slime mold actively adapts its flows as to maximize transport. The quantitative description of flows in P. polycephalum enables a new view on the slime molds growth dynamics during the encounter of food or toxins and how their location can be “remembered”, an important step to perform an informed decision during an individuals network growth and adaptation.
Special seminar - Fereshte Ghahari, Columbia University, "Transport and Thermoelectric Studies of Correlated Phenomena in Graphene"
Mar 14, 2014 · 1:30 p.m.– 2:30 p.m. · Jadwin A06
The observation of correlated electron physics in graphene is mostly limited by strong electron scattering that is caused by charge impurities. We fabricate devices in which electrically contacted and electrostatically gated graphene flakes are either suspended over a SiO2 substrate or deposited on a hexagonal boron nitride layer such that a drastic suppression of disorder is achieved. The mobility of our graphene flakes exceeds 100,000 cm2/Vs. This very high mobility allows us to observe previously inaccessible transport regimes. In particular, we succeeded to observe the fractional quantum Hall Effect for the first time, hereby supporting the existence of interaction induced correlated electron states in the presence of a magnetic field. We were able to measure the energy gap associated with the fractional ν=1/3 state. This gap is at least 3 times larger than that of the 2DEGs in the best quality GaAs heterojunctions in a similar field range.
In addition, at low carrier density graphene becomes an insulator with an energy gap tunable by a magnetic field. The insulating behavior at the charge neutrality point is independent of the in plane magnetic field indicating that the ν=0 quantum hall state in graphene is not spin polarized. Apart from that, we probed the e-e correlations in graphene by means of thermopower measurements. Our results show that at high temperatures the measured thermopower deviates from the generally accepted Mott's formula and that this deviation increases for samples with higher mobility. We quantify this deviation in both the degenerate and the non-degenerate regime using Boltzmann transport theory. We consider different scattering mechanisms in the system including electron-electron scattering.
Mar 17, 2014 · 1:15 p.m.– 2:30 p.m. · Jadwin A10
Much interest in the superconducting proximity effect in 3D topological insulators (TIs) has been driven by the potential to induce exotic Majorana bound states. Most candidate materials for 3D TI, however, are bulk metals, with bulk states at the Fermi level coexisting with well-defined surface states exhibiting spin-momentum locking. In such topological metals, the proximity effect can differ qualitatively from that in TIs. In this talk, I will first discuss how topological metal as we define it interpolates between topological insulator and trivial metal. Then I will discuss how a topological metal, which is not an ideal topological insulator, is better than ideal for superconducting proximity effect.
High Energy Theory Seminar- IAS - Ilias Cholis, Fermilab - “Indirect Detection of Wino Dark Matter: Multichannel Detection Study”
Mar 17, 2014 · 2:30 p.m.– 3:30 p.m. · Bloomberg Lecture Hall - Institute for Advanced Study
TeV scale Wino, provides a possible Dark Matter candidate in the context of the Minimal Supersymmetric Standard Model. Such a dark matter candidate evades all current direct detection and collider bounds and can only be probed through its annihilation products giving indirect detection signals. I will present a multichannel analysis of these indirect signals, including one-loop electroweak and Sommerfeld enhancement corrections affecting both the annihilation cross-section and the spectra of the end products of these annihilations. I derive limits from cosmic ray antiprotons and positrons, from continuum galactic and extragalactic diffuse gamma-ray spectra, from the absence of a gamma-ray line feature at the galactic center above 500 GeV in energy, from gamma-rays toward nearby dwarf spheroidal galaxies and from CMB power-spectra. Additionally, I will discuss the future prospects for neutrino observations toward the inner Galaxy and from antideuteron searches. On each of these indirect detection probes, an important aspect is the relevance of astrophysical uncertainties, that can impact the strength and robustness of the derived limits. Taking all above into consideration, Wino as a dark matter candidate is excluded in the mass range bellow ~800 GeV from antiprotons and between 1.8 and 3.5 TeV from the absence of a gamma-ray line toward the galactic center; with limits from other indirect detection probes confirming the main bulk of the excluded mass ranges.
Mar 24, 2014 · 2:30 p.m.– 3:30 p.m. · PCTS Seminar Room
Math Physics Seminar, Benjamin Schlein, "From BCS-theory to the Gross-Pitaevskii equation for the evolution of dilute fermion pairs"
Mar 25, 2014 · 4:30 p.m.– 6:00 p.m. · Jadwin A06
We consider a system of fermions interacting through a potential admitting a bound state in the low density limit.
Assuming the energy to be sufficiently small, we show that particles form pairs, exhibiting Bose-Einstein condensation and evolving according to the time-dependent Gross-Pitaevskii equation.
Mar 27, 2014 · 4:30 p.m.– 6:00 p.m. · Jadwin A10
Hamilton Lecture - Samuel Ting, MIT, "The Latest Results from the Alpha Magnetic Spectrometer on the International Space Station"
Apr 3, 2014 · 8:00 p.m.– 9:30 p.m. · McDonnell A02
The Alpha Magnetic Spectrometer (AMS) is a multipurpose particle physics detector that was installed on the International Space Station in May 2011. More than 50 billion cosmic ray events have been collected. The latest findings will be presented.
High Energy Theory Seminar - Roberto Bonezzi, University of Bologna, Italy - "Higher Spins on (A)dS in the worldline formalism"
Apr 4, 2014 · 1:30 p.m.– 2:45 p.m. · PCTS Seminar Room
"In this talk I study the one loop effective action for a class of higher spin fields by using a first-quantized description. The latter is obtained by considering spinning particles, characterized by an extended local supersymmetry on the worldline. Quantizing the model on a circle with (A)dS target space allows us to produce a useful representation of the one loop effective action. In particular, we extract the first few heat kernel coe
fficients for arbitrary even spacetime dimension D and for spin S with rectangular Young tableau.
In the second part of the talk I will examine the dimensional reduction on a circle of the former model in flat space. It describes massive HS fields in odd dimensions in terms of Fierz-Pauli equations, while in the massless limit it produces a multiplet of massless fields, described by various Young tableaux, obeying Fronsdal-Labastida equations. The model can be consistently coupled to (A)dS spaces, although the constraint algebra becomes nonlinear."
Math Physics Seminar, Saidakhmat Lakaev, "Threshold effects of the two and three-particle Schroedinger operators on lattices"
Apr 8, 2014 · 4:30 p.m.– 5:30 p.m. · Jadwin A06
Efimov's effect for a system of three particles moving on three-dimensional lattice and interacting via pairwise short-range potentials is studied. The following new results will be presented:
(i). Infinitude of the number of eigenvalues (Efimov's effect) for zero quasi-momentum, and its finiteness for non-zero values of the quasi-momentum. (ii).The corresponding asymptotics for the number of eigenvalues.
Hamilton Colloquium Series - Mikhail Lukin, Harvard University, "Quantum Dynamics of Strongly Interacting Systems"
Apr 10, 2014 · 4:30 p.m.– 6:00 p.m. · Jadwin A10
Apr 14, 2014 · 1:15 p.m.– 2:30 p.m. · PCTS Seminar Room