Applied Physics / Physics Colloquium

Applied Physics/Physics Colloquium: Quantum mechanical bounds on transport and chaos

Topic: 
Quantum mechanical bounds on transport and chaos
Abstract / Description: 

Transport in strongly quantum systems is challenging to understand. I will describe a recently obtained bound on transport in terms of a characteristic quantum velocity (the Lieb-Robinson velocity) and the local thermalization time. This bound sheds some light on experiments in both condensed matter systems and ultracold atomic gases. At finite temperatures, a more powerful velocity is the so-called butterfly velocity, that is intimately related to quantum chaos. This velocity is still poorly understood; I will present some forthcoming results that constrain the temperature dependence of the butterfly velocity in terms of the underlying quantum scrambling of the system.

Date and Time: 
Monday, October 8, 2018 - 4:15pm
Venue: 
Spilker 232

Applied Physics/Physics Colloquium: Tentative title: "Searching for Dark Sectors"

Topic: 
Tentative title: "Searching for Dark Sectors"
Abstract / Description: 

TBA


 

Aut. Qtr. Colloq. committee: R. Blandford (Chair), A. Kapitulnik, R. Laughlin, L. Senatore
Location: Hewlett Teaching Center, Rm. 200

Date and Time: 
Tuesday, November 13, 2018 - 4:30pm
Venue: 
Hewlett 200

Applied Physics/Physics Colloquium: Visiting Newton's Atelier before the Principia, 1679-1684

Topic: 
Visiting Newton's Atelier before the Principia, 1679-1684
Abstract / Description: 

Newton's Principia ignited the Scientific Revolution, but the work-sheets and sketches showing how he composed his masterpiece have been lost. Fortunately, he left behind enough clues to make it possible to give a plausible reconstruction of how he did it. Surprisingly, such a reconstruction has not been attempted before. In the winter of 1679, Robert Hooke initiated a correspondence with Newton outlining the physics of planetary motion. But Hooke was unable to formulate his concepts in mathematical form, and afterward, Newton accomplished this formulation, which allowed him to give a geometrical expression for the passage of time, thus laying the foundations for the Principia. On Dec.10, 1684, four months after a visit of Edmond Halley, Newton sent the first manuscripts for the Principia to the London Royal Society, which he had made "designedly abstruse to be understood only by able Mathematicians". This lack of clarity remains up to the present time. In his talk, I will show, however, that with simply a pencil and a ruler, and without any calculus, good approximations of orbits for central forces can be calculated graphically that also clarify the content of the Principia.


 

Aut. Qtr. Colloq. committee: R. Blandford (Chair), A. Kapitulnik, R. Laughlin, L. Senatore
Location: Hewlett Teaching Center, Rm. 200

Date and Time: 
Tuesday, October 23, 2018 - 4:30pm
Venue: 
Hewlett 200

Applied Physics/Physics Colloquium: Botswana to Bolivia - The Life of an Itinerant Science Educator

Topic: 
Botswana to Bolivia - The Life of an Itinerant Science Educator
Abstract / Description: 

Ranging across Botswana, Bolivia, Nepal, Denmark, The Navajo Nation, and small-town New Jersey, the intricacies of being an international science educator are explored. Does everyone think and communicate as "we" do? How can we maintain our sanity in an increasingly insane world? What are ways that we can best communicate scientific knowledge? These topics are explored in a web of poignant and often humorous anecdotes. The speaker, award-winning educator Phil Deutschle, holds degrees in Physics and Astronomy, is the author of, "The Two-Year Mountain: A Nepal Journey" and "Across African Sand: Journeys of a Witch-Doctor's Son-in-Law," and is the producer of the feature-length documentary, "Searching for Nepal."


 

Aut. Qtr. Colloq. committee: R. Blandford (Chair), A. Kapitulnik, R. Laughlin, L. Senatore
Location: Hewlett Teaching Center, Rm. 200

Date and Time: 
Tuesday, October 16, 2018 - 4:30pm
Venue: 
Hewlett 200

Applied Physics/Physics Colloquium: A High Energy View of the Extreme Universe

Topic: 
A High Energy View of the Extreme Universe
Abstract / Description: 

In the past 10 years, high energy gamma-ray astrophysics has undergone a renaissance. Dramatically improved capabilities from both ground based and space based observatories have combined to unveil dozens of new classes of gamma-ray emitters among the thousands of new sources, and studied each one with unprecedented spatial and spectral capabilities. Continuous monitoring of the high-energy gamma-ray sky has uncovered numerous outbursts from active galaxies, gamma-ray bursts and the discovery of transient sources in our galaxy – some with surprising counterparts. In this talk I will review some of the science highlights from the past decade with an emphasis on the surprises and remaining open questions.


 

Aut. Qtr. Colloq. committee: R. Blandford (Chair), A. Kapitulnik, R. Laughlin, L. Senatore
Location: Hewlett Teaching Center, Rm. 200

Date and Time: 
Tuesday, October 9, 2018 - 4:30pm
Venue: 
Hewlett 200

Applied Physics/Physics Colloquium: Photovoltaic Restoration of Sight in Retinal Degeneration

Topic: 
Photovoltaic Restoration of Sight in Retinal Degeneration
Abstract / Description: 

Retinal degenerative diseases lead to blindness due to loss of the "image capturing" photoreceptors, while neurons in the "image-processing" inner retinal layers are relatively well preserved. Information can be reintroduced into the visual system using electrical stimulation of the surviving inner retinal neurons. Some electronic retinal prosthetic systems have been already approved for clinical use, but they provide low resolution and involve very difficult implantation procedures.


We developed a photovoltaic subretinal prosthesis which converts light into pulsed electric current, stimulating the nearby inner retinal neurons. Visual information is projected onto the retina from video goggles using pulsed near-infrared (~880nm) light. This design avoids the use of bulky electronics and wiring, thereby greatly reducing the surgical complexity. Optical activation of the photovoltaic pixels allows scaling the implants to thousands of electrodes.
In preclinical studies, we found that prosthetic vision with subretinal implants preserves many features of natural vision, including flicker fusion at high frequencies (>20 Hz), adaptation to static images, center-surround organization and non-linear summation of subunits in receptive fields, providing high spatial resolution. Initial results of the clinical trial with our implants (PRIMA, Pixium Vision) having 100mm pixels, as well as preclinical measurements, confirm that spatial resolution of prosthetic vision can reach the sampling density limit.


For a broad acceptance of this technology by millions of patients who lost central vision due to age-related macular degeneration, visual acuity should exceed 20/100, which requires pixels smaller than 25mm. I will describe the fundamental limitations in electro-neural interfaces and 3-dimensional configurations which should enable such a high spatial resolution. Ease of implantation of these wireless modules, combined with high resolution opens the door to highly functional restoration of sight.


Aut. Qtr. Colloq. committee: R. Blandford (Chair), A. Kapitulnik, R. Laughlin, L. Senatore

Location: Hewlett Teaching Center, Rm. 200

Date and Time: 
Tuesday, October 2, 2018 - 4:30pm
Venue: 
Hewlett 200

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

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