Applied Physics / Physics Colloquium

Applied Physics/Physics Colloquium: Nuclear Geochronology and the Age of the Earth

Topic: 
Nuclear Geochronology and the Age of the Earth
Abstract / Description: 

How Old Is Earth? Because Earth formed by protracted accretion of planetestimals, asking the age of our planet is in some ways akin to asking your friends theirs and in other ways different. While your pals are unlikely to date themselves from the moment of conception, we can use U-Pb dating to pinpoint the arrival of our solar system to the formation of the first solids in primitive meteorites that condensed from the circumstellar disk at 4,567.2±0.5 million years (Ma). The timing of volatile loss from parent bodies constrains Earth to have accreted most of its mass by 4,550 Ma from impactors broadly similar in composition to meteorites but, surprisingly, of a class not yet recognized. Whereas your pals almost certainly know the day they emerged from the womb, the continuous mobility of our planet has erased any vestige of its origin. Clues remain nonetheless. Sixty years ago, Clair Patterson argued that the similarity of Pb isotopes between terrestrial rocks and meteorites established Earth's age as 4550 Ma. While his age was approximately correct, he was right for the wrong reason. Recently, two approaches have more clearly constrained an upper age bound to Earth formation; 182Hf-182W dating of core formation at ca. 4,540 Ma and 176Lu-176Hf data from terrestrial and lunar zircons as old as 4,380 Ma that require primary differentiation on both bodies to have ended by 4,510 Ma. The question of Earth's age remains of societal import as about half the population of our country believes that it is less than 10,000 years old and arose in the fashion described in Genesis. But creationists are not alone in promulgating origin myths. In the absence of any empirical evidence, the scientific community long coalesced around the view that the first (~500 Ma) of Earth history saw a continuously molten surface disrupted only by extraterrestrial impacts. Those ancient zircons noted above are seriously challenging that longstanding paradigm.

Date and Time: 
Tuesday, September 25, 2018 - 4:30pm
Venue: 
Hewlett 200

Applied Physics/Physics Colloquium: GW170817: Hearing and Seeing a Binary Neutron Star Merger

Topic: 
GW170817: Hearing and Seeing a Binary Neutron Star Merger
Abstract / Description: 

With the discovery of GW170817 in gravitational waves, and the discovery of an associated short gamma-ray burst, and the discovery of an associated optical afterglow, we have finally entered the era of gravitational-wave multi-messenger astronomy. We will discuss LIGO/Virgo's detection of this binary coalescence and focus on some of the scientific implications, including insight into the origin of gold and platinum in the universe, tests of black holes and general relativity, elucidation of the formation mechanisms for black holes and neutron stars, and the first standard siren measurement of the Hubble constant.

Date and Time: 
Tuesday, May 29, 2018 - 4:30pm
Venue: 
Hewlett 201

Applied Physics/Physics Colloquium: The IceCube Neutrino Observatory and the Beginning of Neutrino Astrophysics

Topic: 
The IceCube Neutrino Observatory and the Beginning of Neutrino Astrophysics
Abstract / Description: 

The IceCube Neutrino Observatory is the world's largest neutrino detector, instrumenting a cubic kilometer of ice at the geographic South Pole. IceCube was designed to detect high-energy astrophysical neutrinos from potential cosmic ray acceleration sites such as active galactic nuclei, gamma ray bursts and supernova remnants. IceCube announced the detection of a diffuse flux of astrophysical neutrinos in 2013, including the highest energy neutrinos ever detected. The sources of these neutrinos are as yet unknown, and IceCube continues to collect data and to collaborate with multi messenger partners in order to explore the neutrino sky. I will discuss the latest results from IceCube and discuss prospects for future upgrades and expansions of the detector.

Date and Time: 
Tuesday, May 22, 2018 - 4:30pm
Venue: 
Hewlett 201

Applied Physics/Physics Colloquium: Quantum Computing with Trapped Ions

Topic: 
Quantum Computing with Trapped Ions
Abstract / Description: 

Individual atoms are standards for quantum information technology, acting as qubits that have unsurpassed levels of quantum coherence, can be replicated and scaled with the atomic clock accuracy, and allow near-perfect measurement. Atomic ions can be confined by silicon-based chip traps with lithographically-defined electrodes under high vacuum in a room temperature environment. Entangling quantum gate operations can be mediated with control laser beams, allowing the qubit connectivity graph to be reconfigured and optimally adapted to a given algorithm or mode of quantum computing. Existing work has shown >99.9% fidelity gate operations, fully-connected control with up to about 10 qubits, and quantum simulations with over 50 qubits. I will speculate on combining all this into a single universal quantum computing device that can be co-designed with future quantum applications and scaled to useful dimensions.

Date and Time: 
Tuesday, May 15, 2018 - 4:30pm
Venue: 
Hewlett 201

Applied Physics/Physics Colloquium: Large Volume 3D Imaging by FIBSEM and Cryo-Fluorescence for Cell Biology and Neural Circuits

Topic: 
Large Volume 3D Imaging by FIBSEM and Cryo-Fluorescence for Cell Biology and Neural Circuits
Abstract / Description: 

3D Electron microscopy volume data can be acquired by a variety of approaches. Focused Ion beam – scanning electron microscopy, FIBSEM, offers no limitation on section thickness, so that isotropic voxels with 8 nm or less sampling in x,y,z dimensions can be acquired. The FIBSEM, which is normally limited to a couple days of continuous operation, was refined to enable year-long reliable data acquisition needed for the large volumes of neural imaging and the fly brain connectome. Concurrently, this capability opens a new regime where entire cells can be imaged with 4 nm voxel sampling, thereby surpassing partial cell or section limitations to complete cell data. The heavy metal staining for EM contrast gives spatially detailed but generic black and white rendering of protein and membrane defined structures. On the other hand, fluorescence microscopy is highly protein specific, by labeling only a tiny subset (1-3) of the thousands of constituent proteins of the cell. Most 99.9% of the cell remains dark. Correlated cryogenic fluorescence microscopy offers a way to combine both without compromising the quality of either EM or fluorescence image. Fluorescent properties at low temperatures (down to 10K) include new regimes of stable fluorescence with highly reduced bleaching, new blinking regimes, good contrast ratios useable for PALM, nonlinearity to excitation power, and photo-reactivation. Multicolor 3D structured illumination SIM images can be acquired on such samples and 2 color, 3D PALM images offer even higher resolution. Examples of such correlative Cryo SIM/PALM and FIBSEM images will be presented on cultured cells.

Date and Time: 
Tuesday, May 1, 2018 - 4:30pm
Venue: 
Hewlett 201

Applied Physics/Physics Colloquium: Ultracold Atom Quantum Simulations: From Exploring Low Temperature Fermi-Hubbard Phases to Many-body Localization

Topic: 
Ultracold Atom Quantum Simulations: From Exploring Low Temperature Fermi-Hubbard Phases to Many-body Localization
Abstract / Description: 

Ultracold-atom model-systems offer a unique way to investigate a wide range of many-body quantum physics in uncharted regimes. Quantum gas microscopy enables us to "zoom in" both, in space and time, on a single particle level. We can explore many-body quantum physics in regimes that are not computationally accessible. In my talk I will present an overview of recent experiments, including the first observation of an anti-ferromagnetic phase of Fermions in an optical lattice, and the observation of many-body localization.

Date and Time: 
Tuesday, April 24, 2018 - 4:30pm
Venue: 
Hewlett 201

Applied Physics/Physics Colloquium: Reverse Engineering the Universe

Topic: 
Reverse Engineering the Universe
Abstract / Description: 

Prof. Andrei Linde of the Stanford Physics Department will give the Applied Physics/Physics colloquium on Tues., May 8, 2018 entitled "Reverse Engineering the Universe."

Date and Time: 
Tuesday, May 8, 2018 - 4:30pm
Venue: 
Hewlett 201

Applied Physics/Physics Colloquium: Demonology: The Curious Role of Intelligence in Physics & Biology

Topic: 
Demonology: The Curious Role of Intelligence in Physics & Biology
Abstract / Description: 

For the lion's share of its history, physics analyzed the inanimate world. Or, that is the view it has of itself. Careful reflection, though, shows that physics regularly invoked an expressly extra-physical agency—intelligence—in its efforts to understand even the most basic physical phenomena. I will survey this curious proclivity, noting that similar appeals to intelligent "demons" go back to Laplace's theory of chance, Poincaré's discovery of deterministic chaos in the solar system, and Darwin's explanation of the origin of biological organisms in terms of natural selection. Today, we are on the verge of a new physics of information that will transform this bad "demonology" to a constructive, perhaps even an engineering, paradigm that explains information processing embedded in the natural world. In the process I will show how deterministic chaos arises in the operation of Maxwell's Demon and outline nanoscale experimental implementations ongoing at Caltech's Kavli Nanoscience Institute.

Date and Time: 
Tuesday, April 17, 2018 - 4:30pm
Venue: 
Hewlett 201

Applied Physics/Physics Colloquium: Top Quarks: The New Flavor

Topic: 
Top Quarks: The New Flavor
Abstract / Description: 

The Large Hadron Collider is providing an enormous dataset of proton-proton collisions at the highest energies ever achieved in a laboratory.

With our new ability to study the Higgs boson and the unprecedentedly large sample of top quarks, a new frontier has opened: the flavor physics of the top quark - at heart, the question of how the top quark interacts with the Higgs field. We can start to ask questions such as whether the Higgs field is the unique source of the top quark's mass and whether there are unexpected interactions between the top quark and the Higgs boson. The answers to these questions will shed light on what may lie beyond the particle physics Standard Model and have cosmological implications.

Date and Time: 
Tuesday, April 10, 2018 - 4:30pm
Venue: 
Hewlett 201

Applied Physics/Physics Colloquium: The Search for Dark Energy and NASA’s WFIRST mission

Topic: 
The Search for Dark Energy and NASA’s WFIRST mission
Abstract / Description: 

Over the last twenty years, there has been growing evidence that our universe is dominated by dark energy. The nature of this dark energy remains a mystery. Is it the signature of the breakdown of general relativity or vacuum energy associated with quantum gravity? I will review the current observations and note the intriguing tensions between measurements based on the cosmic microwave background (CMB) and local measurements of the expansion rate of the universe and the amplitude of density fluctuations. I will then discuss on-going and upcoming CMB experiments and the role of the WFIRST mission in studying the nature of dark energy. I will also discuss the broader scientific mission of the WFIRST mission and its current status.

Date and Time: 
Tuesday, March 13, 2018 - 4:30pm
Venue: 
Hewlett 201

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