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Tim Linden (Ohio State University) Thu. October 4th, 2018
4:00 pm-5:00 pm

2018 Michelson Postdoctoral Prize Lecture 3: Colloquium 

Indirect Searches for Weakly-Interacting Massive Particles

Recent observations at gamma-ray and radio energies, as well as local observations of charged cosmic-rays, have placed increasingly stringent constraints on the annihilation cross-section of Weakly Interacting Massive Particle (WIMP) dark matter. Excitingly, these studies have begun to rule out the infamous “thermal annihilation cross-section”, where WIMP models are expected to naturally obtain the observed relic abundance. As expected when multiple cutting-edge observations coincide, there is currently tension between different studies. For example, strong limits from gamma-ray searches in dwarf-spheroidal galaxies lie in significant tension with dark matter explanations for the observed “Galactic Center excess” observed near the center of the Milky Way.

Tim Linden (Ohio State University) Tue. October 2nd, 2018
11:30 am-12:30 pm

2018 Michelson Postdoctoral Prize Lecture 2

The Rise of the Leptons: Emission from Pulsars will Dominate the next Decade of TeV Gamma-Ray Astronomy

HAWC observations have detected extended TeV emission coincident with the Geminga and Monogem pulsars. In this talk, I will show that these detections have significant implications for our understanding of pulsar emission. First, the spectrum and intensity of these “TeV Halos” indicates that a large fraction of the pulsar spindown energy is efficiently converted into electron-positron pairs. This provides observational evidence necessitating pulsar interpretations of the rising positron fraction observed by PAMELA and AMS-02.

Tim Linden (Ohio State University) Mon. October 1st, 2018
12:45 pm-1:45 pm

Michelson Postdoctoral Prize Lecture 1

Astrophysical Signatures of Dark Matter Accumulation in Neutron Stars

Over the past few decades, terrestrial experiments have placed increasingly strong limits on the dark matter-nucleon scattering cross-section. However, a significant portion of the standard dark matter parameter space remains beyond our reach. Due to their extreme density and huge gravitational fields, neutron stars stand as optimal targets to probe dark matter-nucleon interactions. For example, over the last few years, the mere existence of Gyr-age neutron stars has placed strong limits on models of asymmetric dark matter. In this talk,

Liang Wu, UC Berkeley, MPPL3, Antiferromagnetic resonance and in-gap terahertz continuum in Kitaev Honeycomb magnet α−RuCl3 Fri. September 15th, 2017
12:45 pm-1:45 pm

Antiferromagnetic resonance and in-gap terahertz continuum in Kitaev Honeycone magnet α−RuCl3

Spin-1/2 moments in the antiferromagnetic Mott insulator α-RuCl3 are coupled by strongly anisotropic bond-dependent exchange interactions on a honeycomb lattice. Intense study of α- RuCl3 by inelastic scattering has been driven by the proposal that its low energy excitations may be adiabatically connected to the Majorana quasiparticles that emerge in the exact solution of the Kitaev spin liquid model. In my talk, I will present optical absorption measurements using time- domain terahertz spectroscopy in the range 0.3 to 10 meV that reveal several new features of the low-energy spectrum of α-RuCl3 [1].

Liang Wu (Berkeley); Michelson Postdoctoral Prize Lecture Thu. September 14th, 2017
4:00 pm-5:00 pm

Quantized electro-dynamical responses in topological materials

Although solid-state systems are usually considered “dirty” with impurities and imperfections, it is still the case that macroscopic, quantized phenomena can be observed in the form of the Josephson effect in superconductors and the quantum Hall effect in 2DEG. Combinations of these measurements allow you to determine Planck’s constant and the fundamental charge in a solid-state setting. In my talk, I will show you the observation of a new quantized response in units of the fine structure constant in a new class of material so called “topological insulators” (Tis). First,

Liang Wu, University California Berkeley, MPPL2,Giant nonlinear optical responses in Weyl semimetals Tue. September 12th, 2017
11:30 pm-12:30 pm

Giant nonlinear optical responses in Weyl semimetals

Recently Weyl quasi-particles have been observed in transition metal monopnictides (TMMPs) such as TaAs, a class of noncentrosymmetric materials that heretofore received only limited attention. The question that arises now is whether these materials will exhibit novel, enhanced, or technologically applicable properties. The TMMPs are polar metals, a rare subset of inversion- breaking crystals that would allow spontaneous polarization, were it not screened by conduction electrons. Despite the absence of spontaneous polarization, polar metals can exhibit other signatures, most notably second-order nonlinear optical polarizability, leading to phenomena such as second-harmonic generation (SHG).

Liang Wu, University California Berkeley, MPPL1, Low-energy Electrodynamics of 3D Topological Insulators Mon. September 11th, 2017
12:45 pm-1:45 pm

Low-energy Electrodynamics of 3D Topological Insulators

 

Topological insulators (TIs) are a recently discovered state of matter characterized by an “inverted” band structure driven by strong spin-orbit coupling. One of their most touted properties is the existence of robust “topologically protected” surface states.  I will discuss what topological protection means for transport experiments and how it can be probed using the technique of time- domain THz spectroscopy applied to 3D TI thin films of Bi2Se3.  By measuring the low frequency optical response, we can follow their transport lifetimes as we drive these materials via chemical substitution through a quantum phase transition into a topologically trivial regime [1].

Lucile Savary (MIT) — Michelson Postdoctoral Prize Lecturer Fri. January 27th, 2017
12:45 pm-1:45 pm

Quantum Loop States in Spin-Orbital Models on the Honeycomb and Hyperhoneycomb Lattices

In the quest for quantum spin liquids, the challenges are many: neither is it clear how to look for nor how to describe them, and definitive experimental examples of quantum spin liquids are still missing. In this talk I will show how to devise a realistic model on the honeycomb lattice whose ground state realizes Haldane chains whose physical supports fluctuate, hence naturally providing the hallmark “fractional excitations” of quantum spin liquids. When taken to the three-dimensional hyperhoneycomb lattice, the ground state becomes a full-fledged symmetry-enriched U(1) quantum spin-orbital liquid,

Lucile Savary (MIT) – Michelson Postdoctoral Prize Lecture Thu. January 26th, 2017
4:00 pm-5:00 pm

Quantum Spin Liquids

The search for truly quantum phases of matter is one of the center pieces of modern research in condensed matter physics. Quantum spin liquids are exemplars of such phases. They may be considered “quantum disordered” ground states of spin systems, in which zero point fluctuations are so strong that they prevent conventional magnetic long range order. More interestingly, quantum spin liquids are prototypical examples of ground states with massive many-body entanglement, of a degree sufficient to render these states distinct phases of matter. Their highly entangled nature imbues quantum spin liquids with unique physical aspects,

Lucile Savary (MIT) — Michelson Postdoctoral Prize Lecturer Tue. January 24th, 2017
11:00 am-12:00 pm

Quantum Spin Ice

Recent work has highlighted remarkable effects of classical thermal fluctuations in the dipolar spin ice compounds, such as “artificial magnetostatics.” In this talk, I will address the effects of terms which induce quantum dynamics in a range of models close to the classical spin ice point. Specifically, I will focus on Coulombic quantum spin liquid states, in which a highly entangled massive superposition of spin ice states is formed, allowing for dramatic quantum effects: emergent quantum electrodynamics and its associated emergent electric and magnetic monopoles. I will also discuss how random disorder alone may give rise to both a quantum spin liquid and a Griffiths Coulombic liquid–a Bose glass-like phase.

Lucile Savary (MIT) — Michelson Postdoctoral Prize Lecturer Mon. January 23rd, 2017
4:15 pm-5:15 pm

A New Type of Quantum Criticality in the Pyrochlore Iridates

The search for truly quantum phases of matter is one of the center pieces of modern research in condensed matter physics. Quantum spin liquids are exemplars of such phases. They may be considered “quantum disordered” ground states of spin systems, in which zero point fluctuations are so strong that they prevent conventional magnetic long range order. More interestingly, quantum spin liquids are prototypical examples of ground states with massive many-body entanglement, of a degree sufficient to render these states distinct phases of matter. Their highly entangled nature imbues quantum spin liquids with unique physical aspects,

Ultra-low field MRI – Michael Hatridge Fri. November 13th, 2015
12:30 pm-1:30 pm

Superconducting Quantum Interference Devices (SQUIDs), consisting of two Josephson junctions in a closed superconducting loop, are exquisitely sensitive detectors of magnetic flux. In recent years, we have built magnetic resonance imaging (MRI) scanners based around these detectors which are capable of in vivo imaging at ultra-low (132 microTesla) fields, rather than the several Tesla of conventional MRI. I’ll discuss the challenges and unique advantages of ultra-low field MRI, including enhanced contrast between tissues types such as normal and cancerous prostate tissue which are nearly identical at high fields.

Remote entanglement in superconducting quantum information – Michael Hatridge Thu. November 12th, 2015
4:15 pm-5:15 pm

I’ll review material from the technical lectures and discuss the difference between entanglement via local and ‘remote’ interactions. I’ll discuss possible methods for constructing remote entangling measurements in superconducting quantum information and detail our experimental efforts to remotely entangle qubits via simultaneous readout and phase-preserving amplification.

Josephson junctions and quantum microwave circuits 2: amplifiers – Michael Hatridge Tue. November 10th, 2015
11:30 am-12:30 pm

Here we will take the concepts from lecture one and set out to construct from the same Josephson junctions very weakly non-linear circuits which operate as phase-preserving amplifiers. I’ll discuss some of the numerous chall enges in designing superconducting amplifiers which are robust and simple while achieving nearly ideal performance. I’ll also discuss the quantum-limit of amplification, how closely we can approach it, and how such amplifiers allow precision readout of our quantum bits.

Josephson junctions and quantum microwave circuits 1: qubits and cavities – Michael Hatridge Mon. November 9th, 2015
12:30 pm-1:30 pm

In this lecture I’ll review the basics of the Josephson junction and how it is used as the key building block in superconducting quantum information. I’ll show how we build coupled circuits consisting of a rather non-linear oscillator (which we use as our qubit) coupled to an (almost) linear oscillator/cavity which both shelters the qubit from the outside environment and allows for qubit control and quantum-non-demolition readout.

Sensing the ripples of time – Amar Vutha Fri. October 17th, 2014
12:30 pm-1:30 pm

Almost a century since the dawn of general relativity, we have yet to obtain direct evidence of one of its key predictions: gravitational waves. In this lecture, I will point out how the precisely regular vibrations of atoms in optical atomic clocks can be used to detect the minuscule ripples in time due to gravitational waves. This approach requires portable atomic clocks with high sensitivity and reliable performance. I will describe one approach to realizing such clocks, and lay out the prospects for gravitational wave imaging and astronomy using arrays of satellite-borne clocks. These detectors would complement the efforts to detect gravitational waves using terrestrial (Michelson) interferometers,

Constraining supersymmetry using molecules – Amar Vutha Thu. October 16th, 2014
4:15 pm-5:15 pm

Supersymmetry, and other theories that go beyond the Standard Model of particle physics, often predict the existence of new particles and interactions that act as sources of time-reversal violation. These, in turn, induce asymmetries in the charge distribution of electrons. In this colloquium, I will describe the stringent constraints on such new physics that were recently imposed by precise measurements with the thorium monoxide molecule (ACME Collaboration: Science, Jan 17, 2014). I will explain how polar molecules amplify the minuscule asymmetries of an electron’s charge distribution, how these molecules provide a useful suite of tools for experimenters, and the details of how we made the measurement.

The shape of the electron, and why it matters – Amar Vutha Tue. October 14th, 2014
11:30 am-12:30 pm

The universe, or at least the 5% of it that we understand, is described rather well by the Standard Model of particle physics. Yet even this non-dark sector of the universe conceals a great mystery: // where has all the anti-matter gone? // In this lecture, I will describe the problem and the best solution that we have for it. One of the crucial ingredients of that solution is the prediction of new sources of time-reversal violation. The most sensitive probe of such time-reversal violation is, oddly enough, to be found in small asymmetries in the shape of the electron’s charge distribution.

How big is the proton anyway? – Amar Vutha Mon. October 13th, 2014
12:30 pm-1:30 pm

The proton is a bound state of quarks and gluons, described by the low-energy limit of quantum chromodynamics. Recent measurements using muonic hydrogen have, however, called our understanding of proton physics into question. In this first lecture, I will describe the significant discrepancy that exists between the recent muonic hydrogen measurements and previous measurements on protons — this is the // proton radius puzzle //. In the absence of any feasible theoretical solutions, new experiments might provide the best clues. I shall describe some of the experiments that are attempting to shed light on this puzzle, including our ongoing efforts to measure the proton radius via the Lamb shift in hydrogen atoms.

New Possibilities in Transition-metal oxide Heterostructures – Wei-Cheng Lee Fri. November 8th, 2013
12:30 pm-1:30 pm

Heterojunction, the interface between two dissimilar crystalline materials, has been one of ideal platforms for the two-dimensional electronic systems (2DES). Examples include the quantum Hall effect which was first observed in the semiconductor heterostructures. Recently, a heterostructure made from two transition metal oxides LaTiO3 and SrTiO3 has opened a new door for us to engineer the physical properties of transition metal oxides. In particular, since many of the transition metal oxides are strongly correlated materials, new types of 2DES with strong correlation could emerge from these new oxide interfaces. In this talk, I will first introduce the experimental and theoretical developments in this new field.

To Superconduct or Not to Superconduct; That is the Question? – Wei-Cheng Lee Thu. November 7th, 2013
4:15 pm-5:15 pm

Superconductor, a material losing resistivity below a critical temperature Tc, remains one of the grand challenges in physics. This field began in 1911 with the discovery of superconductivity in mercury at 4.2 K. After the birth of a complete microscopic theory of superconductivity proposed by Bardeen, Cooper, and Schrieffer in 1957, known as BCS theory, it was believed that no materials could have Tc higher than 30 K. The discovery of new classes of superconductors, cuprates in 1986 (which shatter the 30 K barrier) and iron pnictides in 2008, launched an international wave of research to find new materials with higher Tc.

Novel Collective modes in Unconventional Superconductors – Wei-Cheng Lee Tue. November 5th, 2013
12:30 pm-1:30 pm

Unconventional superconductors are materials whose pairing mechanism is not due to the electron-phonon interaction as proposed by BCS theory. Up to date, known unconventional superconductors all exhibit symmetry-broken phases other than superconductivity in their phase diagrams, and it is widely-believed that the fluctuations associated with these symmetry-broken phases hold the key to the pairing mechanism of unconventional superconductors. In this talk, I will summarize our work in studying the collective excitations in cuprates and iron pnictides observed in inelastic neutron scattering and optical measurements. Their implications on the pairing mechanism will be discussed.

Orbital Aspect of Iron-based Superconductivity – Wei-Cheng Lee Mon. November 4th, 2013
12:30 pm-1:30 pm

In this talk, I will focus on the new classes of high-temperature superconductors, iron pnictides. While the magnetic interactions are certainly important in these materials, there have been significant evidences suggesting that the orbital degrees of freedom could play an important role as well. From both theoretical and experimental aspects, I will argue that the orbital degrees of freedom do play a game-changing role in physical properties of iron based superconductors. I will show that at the single particle level, the orbital order in the quasi-1D dxz and dyz bands induces a distortion of the Fermi surface, which could result in the structural phase transition.

Manybody interactions in two-dimensional crystals – Kin Fai Mak Fri. October 19th, 2012
2:30 pm-3:30 pm

The problem of electrons in 2D is one of the most important topics in contemporary condensed matter physics. Coulomb interactions between charge carriers in 2D are dramatically enhanced with the much-reduced dielectric screening compared to their bulk counterpart. Recent advances in the development of atomically thin layers of materials have opened up new opportunities for the study of many-body effects in 2D. In the last talk, we will discuss the observations of strong excitonic effects in graphene and in a valley Hall semiconductor through optical spectroscopy. We will demonstrate the control of Coulomb interactions in such atomic membranes by tuning their dielectric screening through an electrostatic gate.

Beyond graphene: band insulators and topological insulators – Kin Fai Mak Thu. October 18th, 2012
4:15 pm-5:15 pm

Beyond graphene, there exists a rich family of two-dimensional crystals with a broad spectrum of electronic properties, which remain largely unexplored. For instance, a valley Hall semiconductor emerges by breaking the sublattice symmetry in the honeycomb structure. I will present our recent study of monolayer molybdenum disulfide as a protocol. The observation of an indirect-to-direct band gap crossover in the 2D limit and the optical orientation of its long-lived coupled valley-spins will be discussed. Furthermore, in some of the small band gap semiconductors with strong spin-orbit coupling, a new insulating phase with topologically protected surface states appears due to inverted conduction and valence orbitals.

Optics with Dirac electrons – Kin Fai Mak Tue. October 16th, 2012
12:30 pm-1:30 pm

Optical spectroscopy provides an excellent means of understanding the distinctive properties of electrons in the two-dimensional system of graphene. Within the simplest picture, one has a zero-gap semiconductor with direct transitions between the well-known conical bands. This picture gives rise to a predicted frequency-independent absorption of pi alpha = 2.3 %, where alpha is the fine-structure constant. We will demonstrate that this relation is indeed satisfied in an appropriate spectral range in the near infrared, but that at higher photon energies electron-hole interactions significantly modify this result through the formation of saddle-point excitons. Optical spectroscopy also permits a detailed analysis of how the linear bands of graphene,

Novel two-dimensional systems: graphene and beyond – Kin Fai Mak Mon. October 15th, 2012
4:15 pm-5:15 pm

The past few years have witnessed a surge of activities in the study of graphene, a stable sheet comprised of just a single atomic layer of carbon atoms in a honeycomb lattice structure. Indeed, 2010 Nobel Physics Prize recognized two researchers for their pioneering contributions to this field. In this talk we will describe the development of the field and some of the reasons for the intense interest in this new material system, highlighting its unusual electronic dispersion and its distinctive mechanical and chemical properties. We will also discuss recent advances in the fabrication and investigation of other 2D atomic membranes.

To the GUT Scale – the Majorana Neutrino – Lindley Winslow Fri. May 6th, 2011
12:30 pm-1:30 pm

To connect our current results and those from future reactor and long baseline experiments to the preferred theory for neutrinos at the highest energy scales – a theory which explains tiny neutrino masses and enormous asymmetries of matter versus antimatter in the universe- we need one last ingredient. Neutrinos must be their own antiparticle. The third lecture will review this theory and the current generation of double beta decay experiments. The lecture will conclude with a look at a next generation detector proposal.

Download Lindley’s Slides for this talk.

Colloquium: It’s Chooz Time Folks! – Lindley Winslow Wed. May 4th, 2011
4:15 pm-5:15 pm

The last decade has seen a revolution in our understanding of the tiniest fundamental particle the neutrino. The results of several experiments have shown that neutrinos oscillate and therefore have mass. This opens the door for neutrinos and antineutrinos to interact differently, and this little particle to explain the matter antimatter asymmetry in the universe.

The first measurement to explore this possibility is a measurement of the third and smallest mixing angle governing neutrino oscillation θ13. The reactor neutrino experiment Double Chooz is coming online now to make this difficult measurement. The physics of neutrino oscillation and reactor neutrino production will be reviewed.

Three Neutrino Oscillation – The Missing Pieces – Lindley Winslow Tue. May 3rd, 2011
12:30 pm-1:30 pm

Out of the whirlwind of results of the last decade, a new picture is emerging. As we fit together the results, there are several missing pieces. They are the third and smallest mixing angle θ13, the neutrino mass hierarchy, and CP violation in the lepton sector. The second lecture will expand upon the derivations used in the first lecture, and present the experiments that are coming online to address these issues.

Download Lindley’s Slides for this talk

The Neutrino and Oscillation: A Revolution – Lindley Winslow Mon. May 2nd, 2011
4:15 pm-5:15 pm

In the last decade three key experiments KamLAND, SNO, and Super Kamiokande have revolutionized our understanding of the neutrino and have provided the first piece of evidence for physics beyond the standard model. This first lecture will introduce the neutrino, and derive two neutrino oscillation in vacuum and matter. The results of these key experiments will be presented and explained in the context of neutrino oscillation.

Download Lindley’s Slides for this talk.

High-Energy Physics with Low-Energy Symmetry Studies – David Hanneke Fri. May 14th, 2010
12:30 pm-1:30 pm

Discrete symmetries — charge conjugation (C), parity inversion (P), time reversal (T), and their combinations — provide insight into the structure of our physical theories. Many extensions to the Standard Model predict symmetry violations beyond those already known. From the first evidence of P-violation in the 1950s using cold atoms, low-energy, high-precision experiments have quantified existing violations and constrained further ones. In this lecture, I will describe several searches for discrete symmetry violations with low-energy experiments. T-violation, closely related to matter/antimatter asymmetry through the CPT theorem, is tightly constrained by searches for intrinsic electric dipole moments. CPT-violation — the only combination of these symmetries obeyed by the entire Standard Model —

Cavity Control in a Single-Electron Quantum Cyclotron: An Improved Measurement of the Electron Magnetic Moment – David Hanneke Thu. May 13th, 2010
4:15 pm-5:15 pm

Measurements of the electron magnetic moment (the “g-value”) probe the electron’s interaction with the fluctuating vacuum. With a quantum electrodynamics calculation, they provide the most accurate determination of the fine structure constant. Comparisons with independent determinations of the fine structure constant are the most precise tests of quantum electrodynamics and probe extensions to the Standard Model of particle physics. I will present two new measurements of the electron magnetic moment. The second, at a relative uncertainty of 0.28 parts-per-trillion, yields a value of the fine structure constant with a relative accuracy of 0.37 parts-per-billion, over 10-times smaller uncertainty than the next-best methods.

Optical Atomic Clocks – David Hanneke Tue. May 11th, 2010
12:30 pm-1:30 pm

The most precise measurement techniques involve time, frequency, or a frequency ratio. For example, for centuries, accurate navigation has relied on precise timekeeping — a trend that continues with today’s global positioning system. After briefly reviewing the current microwave frequency standards based on the hyperfine structure of cesium, I will describe work towards atomic clocks working at optical frequencies. Among these are standards based on trapped ions or on neutral atoms trapped in an optical lattice. A frequency comb allows the comparison of different optical frequencies and the linking of optical frequencies to more-easily-counted microwave ones. Though still in the basic research stage,

Entangled Mechanical Oscillators and a Programmable Quantum Computer: Adventures in Coupling Two-Level Systems to Quantum Harmonic Oscillators – David Hanneke Mon. May 10th, 2010
4:15 pm-5:15 pm

The two-level system and the harmonic oscillator are among the simplest analyzed with quantum mechanics, yet they display a rich set of behaviors. Quantum information science is based on manipulating the states of two-level systems, called quantum bits or qubits. Coupling two-level systems to harmonic oscillators allows the generation of interesting motional states. When isolated from the environment, trapped atomic ions can take on both of these behaviors. The two-level system is formed from a pair of internal states, which lasers efficiently prepare, manipulate, and read-out. The ions’ motion in the trap is well described as a harmonic oscillator and can be cooled to the quantum ground state.

Simulation, signatures and backgrounds at the LHC – Johan Alwall Thu. April 16th, 2009
12:30 pm-1:30 pm

In the final lecture I will go into details of how to distinguish New Physics at the LHC. I introduce Monte Carlo simulation, the standard tool used for data mining at colliders, and then go on to describe different types of signatures we can expect from new physics, and the Standard Model backgrounds mimicking these signatures. I describe how precision simulation can be achieved, both for the Standard Model backgrounds and the New Physics signals, and present some of the simulation tools available in the community, before concluding the lecture series.

Download Johan’s Slides for this talk.

New Physics at the LHC – Johan Alwall Wed. April 15th, 2009
12:30 pm-1:30 pm

In this second lecture, I further discuss the problems with the Standard Model and why there should be new physics beyond the Standard Model. I will present different classes of solutions, including Supersymmetry, Little Higgs models, and models for Extra Dimensions, as well as their general signatures at the LHC. If time allows, I will end with a discussion about recent ideas for new physics which is not directly motivated by the problems of the Standard Model, including Unparticles and Hidden Valley scenarios.

Download Johan’s Slides for this talk.

Fundamentals of the LHC – Johan Alwall Tue. April 14th, 2009
12:30 pm-1:30 pm

In this introductory lecture I will present why we have built the LHC, and discuss the underlying physics of a hadron collider. This includes the fundamentals of QCD (the theory for the strong interaction), features such as jets and hadronization, and an introduction to the physics of the Standard Model, including Electroweak symmetry breaking. The lecture will be concluded with a discussion about the problems with the Standard Model.

Download Johan’s Slides for this talk.

Hunting for New Physics at the LHC – Johan Alwall Mon. April 13th, 2009
4:15 pm-5:15 pm

At this colloquium I discuss different types of New Physics scenarios, their motivation and how to see them at the LHC. I give an overview of the difficulties associated with distinguishing New Physics among the backgrounds from the Standard Model, and finally present some best- and worst-case scenarios for the LHC.

Download Johan’s Slides for this talk.

Astrophysical probes of dark matter – Roberto Trotta Fri. May 9th, 2008
12:30 pm-1:30 pm

The nature and properties of dark matter are one of the outstanding questions in cosmology. A well-motivated cold dark matter candidate is the lightest supersymmetric particle, the neutralino, whose properties however might remain underconstrained even if supersymmetry is discovered at the LHC in the next few years.

In this talk I will present results from the most complete analysis of the Constrained Minimal Supersymmetric Standard Model (CMSSM) parameter space to date, showing that direct detection experiments have the potential to discover neutralino dark matter by the end of the decade if the CMSSM framework is correct. I will highlight the complementarity between direct dark matter searches,

Precision cosmology for the 21st century – Roberto Trotta Thu. May 8th, 2008
4:15 pm-5:15 pm

The detailed study of cosmic microwave background anisotropies has contributed to transform cosmology into a quantitative, data driven field. Techniques such as weak gravitational lensing and baryonic acoustic oscillations have the potential to become new powerhouses of precision cosmology over the next decade, taking cosmology into a new era of exciting discoveries.

In this talk I will review recent developments towards the achievement of precision cosmology and present the current cosmological concordance model. I will discuss outstanding challenges and future avenues of investigation, and I will survey the evolution of the field in the next 25 years.

Probing dark energy with cosmology – Roberto Trotta Tue. May 6th, 2008
12:30 pm-1:30 pm

In order to pin down the fundamental nature of dark energy, and thus to understand what most of the Universe is actually made of, new and more precise observations are required, along with more efficient and reliable statistical techniques to interpret those observations correctly and to understand the implications they have for our theoretical models of the Universe.

The outstanding challenge posed by the nature and properties of dark energy is giving rise to a flourishing of proposals for new observational campaigns. Type Ia supernovae, gravitational lensing, cluster counts and baryonic acoustic oscillations are some of the techniques available to study dark energy,

Bayes in the sky – Advanced statistical tools for cosmology – Roberto Trotta Mon. May 5th, 2008
12:30 pm-1:30 pm

Increasingly refined cosmological observations, ranging from temperature anisotropies in the cosmic microwave background to the distribution of galaxies in the modern Universe, are leading to the formulation of a “concordance model” of cosmology. As the data sets beocme large and more complex in nature, the statistical tools used to analyse them have become correspondingly more refined, in order to deliver observational answers to many relevant theoretical questions, such as: is dark energy evolving with time? What can we say about the primordial spectrum of density fluctuations? Is the Universe flat? Have we detected hints of new physics in the sky?

Finding and Using Strong Galaxy-Galaxy Lenses in the SDSS – Adam Bolton Fri. May 4th, 2007
11:30 am-12:30 pm
Theory and Phenomenology of Strong Gravitational Lensing – Adam Bolton Thu. May 3rd, 2007
11:30 am-12:30 pm
All I Really Need to Know about Elliptical Galaxies – Adam Bolton Wed. May 2nd, 2007
4:15 pm-5:15 pm
The Modern Practice of Optical Astronomy – Adam Bolton Mon. April 30th, 2007
4:00 pm-5:00 pm
Neutrino Magnetic Moments/ Galactic Positrons and Annihilating Dark Matter – Nicole Bell Fri. May 5th, 2006
12:30 pm-1:30 pm

Neutrino Magnetic Moments:

The detection of a neutrino magnetic moment comparable to present limits would be an unequivocal indication of physics beyond the Standard Model. However, the existence of a neutrino magnetic moment implies contributions to the neutrino mass via electroweak radiative corrections. We derive model-independent upper bounds on neutrino magnetic moments generated by physics above the electroweak scale. For Dirac neutrinos we find a bound several orders of magnitude more stringent than present experimental limits. For Majorana neutrinos the magnetic moment contribution to the mass term is suppressed by Yukawa couplings, thus we do not exclude the possibility of detecting a magnetic moment experimentally.

Neutrino Physics and Astrophysics: What we have learned and what we would like to discover – Nicole Bell Wed. May 3rd, 2006
4:15 pm-5:15 pm

Our knowledge of neutrino physics has undergone dramatic improvement in the last few years. We are now in the position to make confident predictions taking neutrino oscillations into account, opening the possibility to search for truly exotic particle physics within the neutrino sector, and to use neutrinos as reliable probes of astrophysics and cosmology. However, some very fundamental questions about neutrinos remain unanswered, such as whether their masses are of Dirac or Majorana type, or what the absolute neutrino mass scale is (oscillation experiments only reveal information about mass differences). We discuss implications of neutrino mixing for astrophysics and cosmology,

Cosmological Neutrinos: Relic Neutrino Abundance and Neutrino Mass Constraints – Nicole Bell Tue. May 2nd, 2006
12:30 pm-1:30 pm

Neutrinos play unique roles in many epochs of the Universe’s evolution. Important information can be gleaned from neutrino evolution during the big bang nucleosynthesis (BBN) era, for example, the best limit on the Universe’s lepton number results from considering BBN constraints together with large angle neutrino mixing. At later times neutrinos have a significant impact on the cosmic microwave background and large scale structure power spectra. Cosmological data now place the tightest constraints on neutrino mass, though there is scope to evade these limits if the physics of the neutrino sector is non-standard. We outline the wealth of information that can be revealed by studying the sea of relic neutrinos.

Astrophysical Neutrinos: Revealing Neutrino Properties at the Highest Energies – Nicole Bell Mon. May 1st, 2006
12:30 pm-1:30 pm

High energy neutrino astronomy opens a window on the universe that is not accessible with photons, offering an opportunity to obtain information about both astrophysical sources and fundamental particle physics. Neutrino telescopes, such as IceCube, will have the ability to measure both the energy spectrum and flavor content of high energy neutrino fluxes. Flavor ratios can be determined by comparing the rate of shower events to muon tracks, with additional information provided by the observation of tau lepton “lollipop” or “double-bang” events. The peak sensitivities of these interactions occur at different energies, but the flavor ratios can be reliably constructed if a reasonable measurement is made of the spectrum shape.

Luttinger Liquid and Beyond: Crystallization and Free-Spin Regime in 1D – Yaroslav Tserkovnyak Fri. May 13th, 2005
12:30 pm-1:30 pm

In the final talk of the series, I will discuss some fundamental aspects of the physics of interacting electrons in 1D that go beyond the conventional Luttinger-liquid phenomenology. Strongly- interacting low-density electrons form a Wigner-crystal arrangement on finite length scales. Finite wires are experimentally shown to undergo a transition from a Luttinger-liquid order at high electron densities to a crystal-like state below some critical density, which blocks the two-terminal wire conductivity. But even infinite 1D systems cannot be described as Luttinger liquids at low densities and finite temperatures, since nearest-neighbor exchange coupling is exponentially suppressed in the strongly-interacting limit, and electrons are likely to enter an effectively free-spin regime.

Collective Spin Dynamics in Magnetic Nanostructures – Yaroslav Tserkovnyak Thu. May 12th, 2005
4:15 pm-5:15 pm

Ferromagnetism exhibits exciting novel phenomena when the system size is shrunk to submicron scale. Especially interesting are heterostructures with ferromagnetic and nonmagnetic regions combined in multilayer cake-like structures. I will briefly review the field of mesoscopic magnetoelectronics, where such structures are incorporated in Ohmic circuits, focusing on the scattering- matrix approach. The field received its first significant boost with the experimental discovery of giant magnetoresistance, some 20 years ago. Ten years later, theoretical prediction of current- driven magnetic instabilities, with subsequent experimental confirmation, ignited interest in ferromagnetic dynamics in hybrid nanostructures. Since then, many aspects of magnetization dynamics, such as current-driven reversal,

Electron Interference and Correlations as Seen by Momentum-Conserving Tunneling in 1D – Yaroslav Tserkovnyak Tue. May 10th, 2005
12:30 pm-1:30 pm

Tunneling between parallel quantum wires of high purity is a powerful tool in investigating electron correlation effects in one dimension. In particular, it turns out that conductance interference patterns due to the finite size of the tunnel junction encode a wealth of information about the dispersion of the elementary excitations in the system as well as the gate confinement of the wires. Most interestingly, by means of the tunneling interference patterns, one can “see” the spin-charge separation predicted for elementary excitations in 1D. Another interesting interplay between the finite size and electron interactions shedding a light on 1D physics occurs at low energies (voltage and temperature),

Spontaneously-Symmetry-Broken Archimedes Screws – Yaroslav Tserkovnyak Mon. May 9th, 2005
4:15 pm-5:15 pm

In the first technical lecture, I will use the tool box developed in treating time-dependent magnetoelectronic problems to consider a more general class of nonequilibrium phenomena in heterostructures with arbitrary spontaneous symmetry breaking. Motivated by the richness of physics in magnetic nanostructures, we are led to explore analogous phenomena in other symmetry-broken systems. As a first step in this direction, I will discuss a systematic way to construct “Archimedes screws” that are operated by semiclassical control of local orders. The “pumping” is achieved by means of a time-dependent order parameter which characterizes a broken symmetry and is controlled by external fields.

Understanding the Particle Nature of Neutrinos – Karsten Heeger Fri. April 30th, 2004
12:30 pm-1:30 pm

Neutrino mass and oscillation have been convincingly demonstrated in the recent atmospheric, solar, and reactor neutrino data. Some of the fundamental neutrino properties, however, are yet unknown. The data do not tell us the absolute mass scale of neutrinos and whether neutrinos are their own antiparticles. To explain all existing data in neutrino oscillation physics additional right-handed, sterile neutrino states have been postulated. A variety of experiments including direct neutrino mass measurements and double beta-decay experiments are under way to address these questions. Zero-neutrino double beta decay will address the issues of lepton number conservation, the particle-antiparticle nature of neutrinos,

Measuring ϴ13 and the Search for Leptonic CP Violation – Karsten Heeger Thu. April 29th, 2004
12:30 pm-1:30 pm

Non-accelerator neutrino oscillation experiments have provided strong evidence for the mixing of the three known neutrino states. Precision oscillation studies may hold the clue to understanding the matter- antimatter asymmetry in the Universe. Recent experiments have measured the dominant mixing of neutrinos but the subdominant oscillation, the coupling of the electron neutrino flavor to the third mass eigenstate, has not been observed yet. Its corresponding mixing angle ϴ13 is critical for exploring CP violation searches in the lepton sector and may be discovered by next- generation reactor neutrino oscillation experiments. Together, reactor and accelerator experiments will help determine the yet unknown oscillation parameters and search for CP violating effects in the lepton sector.

Recent Discoveries in Neutrino Physics – Karsten Heeger Wed. April 28th, 2004
4:15 pm-5:15 pm

Neutrino mass and mixing are amongst the major discoveries of recent years. From the observation of neutrino flavor change in solar and atmospheric neutrino experiments to the measurements of neutrino mixing with terrestrial neutrinos, recent experiments have revealed new particle properties of neutrinos and provided the first hint of physics beyond the Standard Model of particle physics. These observations have helped solve the long-standing Solar Neutrino Problem, the apparent deficit of the observed electron solar neutrino flux, and have contributed to a better understanding of the role of neutrinos in the Universe. A broad field of neutrino research has emerged in particle,

Evidence for Neutrino Oscillation and Massive Neutrinos: The Resolution of the Solar Neutrino Problem at SNO and KamLAND – Karsten Heeger Mon. April 26th, 2004
12:30 pm-1:30 pm

Unambiguous evidence for novel neutrino properties has recently been obtained from observations of solar and reactor neutrinos. Combined with previous solar neutrino experiments the results from SNO and KamLAND are evidence for neutrino oscillation. The Sudbury Neutrino Observatory (SNO) studies neutrinos from the 8B decay in the Sun to search for neutrino flavor change. SNO’s unique measurement of all neutrino flavors has provided model-independent evidence for the flavor transformation of solar neutrinos. Its results imply that neutrinos have mass. This observation explains the long-standing Solar Neutrino Problem, the deficit of the observed electron solar neutrino flux compared to solar model predictions.

Behind the Scenes with Ultracold Atom Gases and BEC – Brian DeMarco Fri. May 2nd, 2003
12:30 pm-1:30 pm

The field of ultra-cold quantum atom gases began in 1995 with the realization of Bose-Einstein condensation in a dilute alkali atom gas. Four years later, in Deborah Jin’s group at JILA, we created the first atomic Fermi gas. Not only interesting systems in their own right, ultra-cold atom gases have many parallels with condensed matter systems. Ultra-cold atom gases are unique in that the atomic internal and external states can be manipulated with great precision and the interactions between constituent particles are theoretically accessible and can be controlled experimentally.

The traditional route to alkali atom Bose-Einstein condensation (BEC) involves first collecting roughly billions of atoms from a room temperature vapor and cooling them to temperatures between 10-100 mK.

Quantum Behavior of an Atomic Fermi Gas – Brian DeMarco Thu. May 1st, 2003
4:15 pm-5:15 pm

The colloquium will cover my graduate work on creating the first Fermi gas of atoms. The magnetic trapping and evaporative cooling techniques used to produce atomic Bose-Einstein condensation were extended to create the first quantum degenerate Fermi gas of atoms. Evaporatively cooling fermionic atoms is hindered by the fundamental difficulty that identical fermionic atoms do not collide at ultra-cold temperatures (less than a few 100 mK). This complication was overcome by magnetically trapping two spin-states of the fermionic atom 40K which undergo the s-wave collisions necessary for rethermalization during cooling.

The unique properties of binary collisions of fermionic atoms were used to make the first measurement of the 40K s-wave triplet scattering length.

An Atomic Turing Machine: Quantum Computing with Trapped Ions at NIST – Brian DeMarco Wed. April 30th, 2003
12:30 pm-1:30 pm

The basic features of quantum information processing using trapped ions will be briefly reviewed from Lecture 1. Our current work focuses on demonstrating the necessary ingredients to produce a scalable quantum computing scheme and on simplifying and improving quantum logic gates. Along these lines, I will speak about a new set of experiments that was made possible by recent improvements in trap technology. A novel trap with multiple trapping regions was used to demonstrate the first steps towards a fully scalable (multiplexed) quantum computing scheme. Single ions were “shuttled” between trapping regions without disturbing the ion’s motional and internal state,

Quantum Information Processing using Atomic and Optical Systems – Brian DeMarco Mon. April 28th, 2003
12:30 pm-1:30 pm

Quantum information processing is a rapidly emerging field, with development in atomic, photonic, and condensed matter systems underway. Classical computers (the standard computers of today) are inherently limited by memory storage and computational ability. For example, to store the complete quantum state of 300 interacting spin-1/2 particles in classical memory would require more bytes than the estimated number of protons in the universe. The pursuit of quantum computer technology is motivated by overcoming these limitations. The advantage of quantum computers over classical computers arises from the use of the qubit as a fundamental unit of information. Unlike a bit, which can be in one of two states (“0”

Beaming and Jets in Gamma Ray Bursts – Re’em Sari Fri. April 5th, 2002
1:30 pm-2:30 pm

Though the distance scale to Gamma Ray Bursts is now known, the energy is still subject to several orders of magnitude uncertainty due to the possible beaming of the emission. Since the flow is relativistic, with Lorentz factor $\Gamma \gg 1$, the emission is collimated to a narrow cone of half opening angle $1/\Gamma$ around the direction of motion. Observer is therefore unable to tell whether the emission is spherical, at which case the energies of these events is as high as 1054erg, or narrowly collimated with proportionally less energy. During the afterglow, the Lorentz factor is decreasing with time.

Exciting The Eccentricity of Extrasolar Planets – Re’em Sari Thu. April 4th, 2002
4:15 pm-5:15 pm

The detection of extrasolar planets is one of the great scientific discoveries of the past decade. Most of these planets planets move on orbits with substantial eccentricities. The origin of these large eccentricities is an unsolved puzzle. We propose that they result from the exchange of angular momentum and energy between the planets and the disks from which they form. These interactions are concentrated at discrete Lindblad and corotation resonances. We describe the physics of these resonances and their effects on the planets migration and eccentricity evolution. If both resonances are fully active, the rate of eccentricity damping by corotation resonances is slightly larger than its excitation rate by Lindblad resonances and the eccentricity decays.

Theory and Observations of the Afterglow of Gamma Ray Bursts – Re’em Sari Wed. April 3rd, 2002
12:30 pm-1:30 pm

Early on 1997, the field of Gamma Ray Bursts had a dramatic breakthrough. The Italian-Dutch satellite, BeppoSAX, delivered accurate positioning of several events. Dozens of ground based and space based observatories monitored the given position, and found decaying emission in x-ray, optical and radio, lasting for years after the events. These observations, established the distance scale to the explosions and confirmed much of the theoretical understanding given by the fireball model. The afterglow is produced once the relativistic flow, which earlier produced the burst itself, interact with its surrounding. Shock waves are produced, in which particles are accelerated and then emit synchrotron and inverse Compton radiation.

Phenomenology of Gamma Ray Bursts – Re’em Sari Tue. April 2nd, 2002
12:30 pm-1:30 pm

Gamma Ray Bursts emit 1051-1054erg, mostly in Gamma rays around 1MeV. The short timescale variability (down to a ms) implies a very compact source, and therefore high photon density. With these conditions, the optical depth to electron positron pair creation is huge, in contradiction with the observed non thermal spectrum. The only way out of this “compactness problem” is extreme relativistic motion. We show that the sources of Gamma Ray Burst must emit relativistic flows, with Lorentz factor exceeding several hundreds. We describe the generic model, “the fireball model”, for Gamma Ray Bursts,

The Cosmological Constant and Brane Nucleation – Jonathan Feng Fri. April 20th, 2001
12:30 pm-1:30 pm

Present observations favor a small but positive cosmological term. Recent theoretical developments suggest the possibility of fundamental brane degrees of freedom. If these branes are coupled to a three-index gauge field, brane nucleation may neutralize a large cosmological constant, much as pair creation neutralizes an electric field. I consider the possibility that the present cosmological term is the end result of a series of such nucleations.

The Search for Supersymmetry – Jonathan Feng Thu. April 19th, 2001
12:30 pm-1:30 pm

Supersymmetry predicts a partner particle for every known particle. I will present some of the theoretical motivations for expecting the discovery of supersymmetry in the near future at colliders, in precision data, and in dark matter searches, drawing on recently reported anomalies as examples. Finally, I discuss the long-term prospects for supersymmetry.

Particle Physics Implications for Dark Matter – Jonathan Feng Tue. April 17th, 2001
12:30 pm-1:30 pm

Although the cosmological evidence for dark matter is overwhelming and becoming increasingly precise, the nature of dark matter remains a mystery. Particle physics plays an important role, both by suggesting candidates and by imposing powerful constraints. This interplay is especially fruitful in the case of supersymmetry. I will review what we do (and do not) know about supersymmetric dark matter. I will then describe some recent developments and their implications for dark matter searches.

Focus Point Supersymmetry – Jonathan Feng Mon. April 16th, 2001
12:30 pm-1:30 pm

All of supersymmetry phenomenology suffers from the tension between naturalness and low energy constraints. Most attempts to relieve this tension have assumed that naturalness requires sub-TeV superpartners and have attempted to satisfy the low energy constraints by arranging for scalar degeneracy, In this talk, I will describe an alternative proposal: focus point supersymmetry. In this framework, an interesting property of renormalization group equations allows all scalar superpartners to have multi-TeV masses without sacrificing naturalness.

Nanofabrication for Fundamental Physics – Keith Schwab Fri. May 12th, 2000
12:30 pm-1:30 pm

Researchers are taking advantage of the silicon industry’s development of fabrication tools and techniques to construct devices with dimensions comparable or smaller than fundamental physical length scales, such as the Fermi wavevector, quantum-phase coherence lengths, or the thermal phonon wavelength in a dielectric suspended beam. Here I will review some of the basic fabrication techniques by using examples of some important devices that researchers have made. An application of particular interest is the possibility to fabricate a mechanical oscillator which can be prepared in its quantum mechanical ground state. Once this is realized, one has a quantum measurement playground; quantum non-demolition,

Measurement of the Universal Quantum of Thermal Conductance – Keith Schwab Thu. May 11th, 2000
12:30 pm-1:30 pm

We have performed experiments to probe directly the thermal conductance of suspended nanostructures with lateral dimensions ~100nm. It has been recently predicted that at low temperatures, thermal conductance in such a structure approaches a universal value of $\pi^2 k_B^2 \over
       3h$ for each massless, ballistic 1D channel, independent of material characteristics. We have developed ultra-sensitive, low dissipation dc-SQUID-based noise thermometry, and extreme isolation from the electronic environment in order to perform this measurement at temperatures <100mK. We will report our very recent successful measurements of this universal quantum of thermal conductance and the implications for single photon and possibly single phonon calorimetry.

The Josephson Effect in Superfluids – Keith Schwab Tue. May 9th, 2000
12:30 pm-1:30 pm

Since the development of the Superconducting Quantum Interference Device in the late 1960’s it has been appreciated that similar effects should exist in superfluids. In the past 10 years substantial progress has been made in observing these effects in both superfluid 3He and 4He. In this lecture, I will introduce the basic physics of the Josephson effect in superfluids and describe how these very delicate experiments are carried out. These new superfluid devices may have some very interesting applications as ultra-sensitive gyroscopes and possibly as quantum standards. –

SQUID’s and SET’s: Introduction to Quantum Limited Amplifiers and their Application – Keith Schwab Mon. May 8th, 2000
12:30 pm-1:30 pm

The purpose of this lecture is to introduce to the audience the basic ideas of quantum limited amplifiers, SQUIDs and SETs. These devices operate by utilizing fundamental quantum phenomena, which is beautiful and interesting in its own right. This has been harnessed to construct the most sensitive amplifiers known, close to the quantum uncertainty principle. Here I will describe some of the applications of these devices which varies from the position sensor on a multi-ton gravitational wave detector, to measuring the temperature of a nanostructure.

Overview: The 2000 Michelson Postdoctoral Prize Lectures – Keith Schwab Mon. May 8th, 2000
12:30 pm-1:30 pm

Condensed matter systems are beginning to display coherent quantum phenomena, behavior that until now had been only the domain of quantum optics. In fact, researchers have recently succeeded in preparing a Single Electron Transistor (SET) into a quantum superposition. These exciting developments have wide reaching implications to basic quantum theory, Where is the boundary between the classical and the quantum world?, to ultimate measurement limits for gravitational wave detector read-out. The purpose of these technical lectures is to give the audience a primer in the basic physics and advanced tools which are being used to realize these experiments. The colloquium lecture gives an example of how these state-of-the-art measurement techniques are used to observe an exciting new mesoscopic behavior in nanostructures,

Probing the Distant Universe With the Sunyaev-Zel’dovich Effect – Joe Mohr Fri. April 9th, 1999
12:30 pm-1:30 pm
Connections Between Galaxy Clusters and Cosmology – Joe Mohr Thu. April 8th, 1999
12:30 pm-1:30 pm
Cluster Regularity as a Tool to Study Cosmology – Joe Mohr Tue. April 6th, 1999
12:30 pm-1:30 pm
Regularity and Complexity: The Dual Nature of Galaxy Clusters – Joe Mohr Mon. April 5th, 1999
12:30 pm-1:30 pm
Quantifying Entanglement – Christopher Fuchs Sat. February 6th, 1999
12:30 pm-1:30 pm
What Can You Do with Quantum Entanglement? – Christopher Fuchs Fri. February 5th, 1999
12:30 pm-1:30 pm
Sending Classical Information on Noisy Quantum Mechanical Channels – Christopher Fuchs Thu. February 4th, 1999
12:30 pm-1:30 pm
Optimal Quantum Measurements and the Distinguishability of Quantum States – Christopher Fuchs Tue. February 2nd, 1999
12:30 pm-1:30 pm
A Spectroscopic High Energy Particle Detector and a Search for WIMPS – Thomas Walther Sat. April 18th, 1998
12:30 pm-1:30 pm
Remote Velocity and Temperature Profiling in the Ocean – Thomas Walther Sat. April 18th, 1998
12:30 pm-1:30 pm
A Novel Approach to Testing Bell Inequalities – Thomas Walther Fri. April 17th, 1998
12:30 pm-1:30 pm
UV-IR and IR-UV Double Resonance Experiments for the Study of Molecular Dynamics – Thomas Walther Thu. April 16th, 1998
12:45 pm-1:30 pm

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