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Winter 2012 Colloquium Series

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Colloquia are at 4pm, Thursdays, in 100 Willamette Hall and are preceded by coffee, tea, and cookies at 3:40 in the Willamette Atrium.

The organizer of the Winter Term Colloquia is: Hailin Wang

Jan 12, 2012

Matthew Rakher

University of Basel/Switzerland

Quantum Optics with Semiconductor Quantum Dots

Quantum optics is a field devoted to the study of the quantum mechanical interaction of light with matter and has been traditionally investigated using atoms and ions. Semiconductor quantum dots (QDs) have recently developed into an interesting, alternative platform at the intersection of quantum optics and condensed matter physics. Combined with advanced nanofabrication techniques to create ultra-small optical cavities and waveguides, QDs can be used to create bright single photon sources and to explore the coupling between a single emitter and a single photon in cavity quantum electrodynamics (QED). In this talk, I will present experiments demonstrating several cavity QED effects which explicitly utilize the semiconductor nature of the QD. Furthermore, I will present recent experiments on quantum frequency conversion of QD-generated single photons from telecommunications-wavelengths to the visible, which can be an important resource for integrating QDs with other quantum systems. Taken together, these results comprise a versatile set of techniques for the continued development of solid-state emitters for quantum optics and quantum information.

Host: Hailin Wang

Jan 19, 2012

Steven Olmschenk

University of Maryland/NIST/Joint Quantum Inst.

Quantum Information with Atoms and Light

Rapid progress in coherent control of single trapped atomic ions and ensembles of ultracold atoms in optical lattices has enabled more precise atomic physics measurements, a probe of fundamental quantum physics, and progress towards quantum information processing, including the quantum simulation of models from condensed matter. Here I present recent results on approaches towards these ends with both trapped ions and ultracold atoms in optical lattices. Using ytterbium ions coupled to single photons, we demonstrate a quantum teleportation protocol between two distant matter qubits with a measured fidelity of 90%. With atoms in an optical lattice, we perform randomized benchmarking of single qubit operations, measuring an average error per gate of 1.4 x 10^-4. A method to extend the coherence time by cancellation of up to 95% of the differential light shift in the ground state of rubidium is also implemented. Finally, I discuss recent progress towards observing new many-body effects, as well as how all of these operations might be extended for more advanced applications.

Host: Hailin Wang

Jan 26, 2012

Yanwen Wu

University of Texas – Austin

Optical Quantum Computation in Semiconductor Quantum Dot Systems

As the size of transistors quickly and inevitably approaches the atomic scale as predicted by Moore’s law, quantum effects become more relevant and will subsequently hinder further progress in classical computation. The concept of the quantum computer embraces the physics that governs the quantum mechanical nanoscaled world. Rather than adhering to the notion that a computational bit must be either 0 or 1, the quantum bit (qubit) can be 0, 1, or any superposition thereof. This results in a massive parallelism in computation that makes certain quantum algorithms excel above their classical counterparts. An optically driven semiconductor quantum dot system is one of many potential candidates for the realization of a physical quantum computer. I will discuss in this talk the implementation of quantum gates using ultrafast optical excitations in semiconductor quantum dot systems. In particular, I will show how the roles of the amplitude and phase of the optical pulse change when the excitation method changes from that of a transform-limited pulse to a linearly chirped pulse in the adiabatic rapid passage regime.

Host: Hailin Wang

Feb 9, 2012

Stephanie Majewski

Brookhaven National Lab

Surpassing The Standard Model: Searching for Supersymmetry

Since its turn-on in 2009, the Large Hadron Collider has performed tremendously, delivering copious amounts of proton-proton collision data at a center-of-mass energy of 7 TeV. Analyzing these data, the ATLAS experiment has conducted a broad search for Supersymmetry, a compelling theory for physics beyond the Standard Model. No hint of a super-partner has yet been seen, but I will discuss what we’ve ruled out so far, and why we’re not ready to hang up our sparticles.

Host: Eric Torrence, February 14

Feb 16, 2012

Corrinne Mills

Harvard University

The Search for the Standard Model Higgs Boson in the WW to dilepton final state

In December 2011, the CMS and ATLAS experiments presented preliminary results in the search for Standard Model Higgs boson at the LHC, including the first analyses of the full 2011 dataset. Large swaths of possible masses for the Higgs particle are now experimentally disfavored, but combined evidence from multiple final states hints at a signal at low mass (m_Higgs < 130 GeV). I will present the current status and future prospects of the searches for the Standard Model Higgs boson at the ATLAS experiment, focusing on the final state with two W bosons in which each W decays to a charged lepton and a neutrino. This WW dilepton final state has excellent sensitivity over a large range of Higgs masses and contributes significantly to the discovery potential all the way down to the lower bound set by the LEP experiments. Nature has given us a cliffhanger this winter, but with the addition of the 2012 data, we should be able to make a definite statement on the existence, or non-existence, of the Standard Model Higgs boson.

Host: Eric Torrence

Feb 21, 2012

Eric Thrane

University of Minnesota

Warped spacetime

The Laser Interferometer Gravitational-wave Observatory (LIGO) aims to detect minute ripples in the fabric of spacetime known as gravitational waves. Gravitational waves are created in some of the most extreme phenomena in the universe including coalescing neutron stars, supernovae and the birth of the universe. In this way, gravitational-wave measurements tell us about environments, inaccessible in the laboratory, characterized by high energies, high densities, and strong gravitational fields. I describe the science potential of gravitational-wave physics and recent preparations for the upcoming “Advanced LIGO.” I discuss recent milestones and the prospects for near-future detections.

Host: Eric Torrence

Feb 23, 2012

Maiken Mikkelsen

University of California – Berkeley

Spintronics & Nanophotonics for Quantum Information Science

Individual semiconductor quantum dots are attractive systems for the study of fundamental spin dynamics, light-matter interactions, and quantum information applications. A key ingredient for spin-based quantum information processing is the coherent rotation of a spin-state on timescales much faster than the spin coherence time. To achieve this, off-resonant optical pulses are used to create a large effective magnetic field via the optical Stark effect, allowing the coherent rotation of a single electron spin in a quantum dot through arbitrary angles up to pi radians in 30 ps [1]. Non-destructive time-resolved Kerr rotation is used to directly monitor the electron spin dynamics and in addition serves as a sensitive probe of the local nuclear spin environment [2,3]. These experiments demonstrate the sequential initialization, ultrafast manipulation, and detection of a single electron spin in GaAs quantum dot. One of the next challenges for quantum information applications is the creation of on-chip quantum networks. A step towards this goal is the integration of single emitters with nanophotonic structures. Recent experiments demonstrate efficient coupling of a single CdSe/ZnS quantum dot to a deep-subwavelength waveguide revealing strongly enhanced light-matter interactions [4]. These results represent progress towards the implementation of scalable quantum information processing in the solid state.

[1] J. Berezovsky*, M. H. Mikkelsen*, N. G. Stoltz, L. A. Coldren & D. D. Awschalom, Science 320, 349 (2008)
[2] M. H. Mikkelsen, J. Berezovsky, N. G. Stoltz, L. A. Coldren & D. D. Awschalom, Nature Physics 3, 770 (2007)
[3] J. Berezovsky, M. H. Mikkelsen, O. Gywat, N. G. Stoltz, L. A. Coldren & D. D. Awschalom, Science 314, 1916 (2006)
[4] M. H. Mikkelsen*, N. Pholchai*, P. Kolchin*, J. Oh, M. S. Islam & X. Zhang, in preparation

Host: Hailin Wang

Feb 28, 2012

Peter Onyisi

CERN & University of Chicago

The Higgs Search at the Large Hadron Collider

The Standard Model of particle physics describes an extremely successful unification of the electromagnetic and weak forces. However, the mechanism by which the underlying electroweak symmetry is broken has not yet been directly observed. Observation and study of particles associated with this mechanism – in the Standard Model, the Higgs boson – will answer many important questions and may open a window to phenomena beyond the Standard Model, such as dark matter and supersymmetry. The search for the Higgs boson is one of the highest priorities of the LHC experiments. I will discuss the motivation for a Higgs-like mechanism, what we may learn from its discovery and study, and the latest experimental results.

Host: Eric Torrence

Mar 1, 2012

Irfan Bulu

Harvard University

Nano-plasmonics and Nano-photonics: Applications to Enhanced Single Photon Sources

Plasmonics and photonics at the nano-scale offer new possibilities for improving the performance of photonic devices such as lasers, creating new functionality, and building chip-scale integrated optical devices. In the first part of my talk, I will present our recent experimental and theoretical work on plasmonic nano-cavities for efficient, room temperature single photon sources based on nitrogen-vacancy (NV) color centers in diamond. NV center is a stable single photon source even at room temperature, and exhibits long coherence times for both electronic and nuclear spins. As a result, it is a robust quantum system for applications ranging from quantum information processing to nano-scale magnetometry. These applications benefit from large single photon rates, which can be improved by the use of nano-photonic devices. I will discuss various plasmonic cavity designs and show that the emission rate, excitation rate, and collection efficiency from single NV centers can be improved significantly in an extremely small footprint device. Furthermore, I show that our scalable, top-down nanofabrication technique maintains the crucial properties of embedded NV centers, and is therefore compatible with requirements needed for realization of quantum systems based on diamond. In the second part of the talk, I will discuss our work on mid-infrared photonics. The mid-infrared is an exciting wavelength range for on chip photonic devices, with important applications in spectroscopy and gas sensing. We recently developed record high-Q (45,000) photonic crystal cavities on a CMOS compatible platform for trace gas sensing applications. I will discuss some of the methods that we developed in order to improve the quality factors of photonic crystal cavities at mid-infrared (4.5 μm), and report the observation and origin of optical bi-stability at this wavelength range. Finally, I will discuss the prospects for future devices ranging from all-optical signal processing to on chip frequency combs at the mid-infrared.

Host: Hailin Wang

Mar 6, 2012

Jahred Adelman

CERN & Yale University

An excess of needles in the haystack? The hunt for new physics at ATLAS

After the end of the LHC’s 2011 proton-proton run, ATLAS is performing a wide range of exciting searches for new physics. I’ll begin with a brief overview of the current state of the Standard Model, including some discussion of the many pieces of the theory that are incomplete or unsatisfactory. Next I will follow with some history of the techniques used for previous discoveries in particle physics, and will compare those analyses with the latest ATLAS searches; many, if not all, of the techniques are fundamentally the same. After discussing some more sophisticated searches for new physics, I will conclude with prospects for finding new physics during the 2012 LHC run.

Host: Eric Torrence

Mar 8, 2012

Toyoko Orimoto


The Search for the Higgs in the Diphoton Channel with the CMS Detector

The Higgs boson is the last missing piece of the Standard Model of particle physics. As such, the discovery of the Higgs boson is one of the primary goals of the Compact Muon Solenoid Experiment, a general purpose particle detector experiment at the Large Hadron Collider at CERN. Instrumented with a high-precision, high-granularity electromagnetic crystal calorimeter, CMS has been optimized for the discovery of the Higgs in the “golden” two photon decay channel. I present an overview of the Standard Model, as well as the motivation for finding the Higgs boson. I will also describe the CMS detector, focusing on the strengths of the electromagnetic calorimeter, which is crucial for searches with photon final states. Then, I will describe the latest results in the search for the Higgs in the two photon channel, as well as the prospects with 2012 data.

Host: Eric Torrence