Applied Physics / Physics Colloquium

Stanford Friends of Physics Special Lectures

Topic: 
Superconductivity and Quantum Mechanics at a Human Scale
Abstract / Description: 

Superconductivity is perhaps the most spectacular macroscopic quantum phenomenon. A "persistent current" in a ring of superconducting wire will continue to flow forever—a laboratory realization of perpetual motion. A voltage across a junction between two superconductors produces an oscillating current with a frequency that is determined exactly by the voltage and the fundamental constant of quantum mechanics, Planck's constant. Superconductivity is the quintessential example of an "emergent phenomenon" in physics, in which the collective behavior cannot be understood in terms of the properties of any finite collection of microscopic constituents (i.e., electrons). Notable physicists including Einstein, Heisenberg, and Feynman tried and failed for half a century to achieve the basic understanding of superconductivity that was only achieved in the mid 1950's and early 1960's. However, many fundamental issues remain to be resolved, including those related to the more recent discovery of unconventional "high temperature superconductivity" in a variety of synthetic metals, and the construction of coherent superconducting "Q-bits," which act as laboratory realizations of Schrodinger's cat.


 

Greetings, Friends of Physics! We hope some of you can attend the upcoming SITP mini-course by Steven Kivelson, the Prabhu Goel Family Professor of Physics. Professor Kivelson is a leading researcher in theoretical condensed matter physics at the Stanford Institute for Theoretical Physics (SITP).


SITP mini-courses feature SITP faculty members lecturing on their fields and research. The presentations are intended for audiences with an interest in learning about science more deeply than the level of popular media, and some scientific or mathematical background. You are welcome to attend the lectures in person or access them on the web when they are posted (see below).

Date and Time: 
Monday, May 9, 2016 - 7:00pm to 8:30pm
Venue: 
Hewlett 201

Claude E. Shannon's 100th Birthday

Topic: 
Centennial year of the 'Father of the Information Age'
Abstract / Description: 

From UCLA Shannon Centennial Celebration website:

Claude Shannon was an American mathematician, electrical engineer, and cryptographer known as "the father of information theory". Shannon founded information theory and is perhaps equally well known for founding both digital computer and digital circuit design theory. Shannon also laid the foundations of cryptography and did basic work on code breaking and secure telecommunications.

 

Events taking place around the world are listed at IEEE Information Theory Society.

Date and Time: 
Saturday, April 30, 2016 - 12:00pm
Venue: 
N/A

Applied Physics/Physics Colloquium

Topic: 
A New Spin on Superconductivity
Abstract / Description: 

Nearly a hundred years after its discovery, superconductivity remains one of the most intriguing phases of matter. In 1957 Bardeen, Cooper and Schrieffer (BCS) presented their theory of superconductivity, describing this state in terms of pairs of electrons arranged in a spatially isotropic wave function with no net momentum and a spin singlet configuration. Immediately thereafter, a search began to find materials with unconventional superconductivity where pairing deviates from conventional BCS theory. One particular class of unconventional superconductors involves pairs arranged in triplet rather than singlet configurations. Such superconductors may enable dissipationless transport of spin and may also give rise to elementary excitations that do not obey the conventional Fermi or Bose statistics but rather have non-Abelian statistics, where the exchange of two particles transforms the state of the system into a new quantum mechanical state. In this talk I will describe some of our recent experiments that explore the proximity effect between a conventional superconductor and a semiconductor with strong spin-orbit interaction. Using supercurrent interference, we show that we can tune the induced superconductivity continuously from conventional to unconventional that is from singlet to triplet. Our results open up new possibilities for exploring unconventional superconductivity as well as new ways for detecting unconventional pairing in known materials.


Held Tuesdays at 4:30 pm in the William R. Hewlett Teaching Center, room 201.

Refreshments in the lobby of Varian Physics at 4:15 pm.

Spring 2015/2016, Committee: M. Schleier-Smith (Chair), G. Gratta, B. Lev, S. Zhang

Date and Time: 
Tuesday, May 31, 2016 - 4:30pm to 5:30pm
Venue: 
Hewlett 201

Applied Physics/Physics Colloquium

Topic: 
Testing Quantum Systems
Abstract / Description: 

The testing of quantum devices poses unique new challenges: although the description of the quantum state of a system scales exponentially in the size of the system, the laws of quantum mechanics limit the information that can be accessed by measuring the system to be linear in its size. This restriction, together with the mismatch in the computational power of quantum and classical systems appear to rule out any general strategy for the classical testing of quantum devices.

Nevertheless, over the past few years there has emerged a new theory of quantum testing that exploits unique features of quantum mechanics to get around these obstacles. This theory has resulted in provably secure quantum cryptography with untrusted quantum devices and certifiable random number generators. It has also resulted in protocols for testing that a claimed quantum computer is truly quantum. On a more philosophical level, these new protocols shed new light on what it might mean to test quantum mechanics in certain regimes.


 

Held Tuesdays at 4:30 pm in the William R. Hewlett Teaching Center, room 201.

Refreshments in the lobby of Varian Physics at 4:15 pm.

Spring 2015/2016, Committee: M. Schleier-Smith (Chair), G. Gratta, B. Lev, S. Zhang

Date and Time: 
Tuesday, May 24, 2016 - 4:30pm to 5:30pm
Venue: 
Hewlett 201

Applied Physics/Physics Colloquium

Topic: 
Exploring New Frontiers of Quantum Optical Science
Abstract / Description: 

I will discuss recent developments at a new scientific interface between quantum optics, nanoscience and quantum information science. Specific examples include the use of quantum optical techniques for manipulation of individual atom-like impurities at a nanoscale and for realization of hybrid systems combining them with nanophotonic devices. I will discuss how these techniques are used for exploring quantum nonlinear optics and quantum networks, probing non-equilibrium quantum dynamics, and developing new applications such as magnetic resonance imaging with single atom resolution, and nanoscale sensing in biology and material science.


 

Held Tuesdays at 4:30 pm in the William R. Hewlett Teaching Center, room 201.

Refreshments in the lobby of Varian Physics at 4:15 pm.

Spring 2015/2016, Committee: M. Schleier-Smith (Chair), G. Gratta, B. Lev, S. Zhang

Date and Time: 
Tuesday, May 17, 2016 - 4:30pm to 5:30pm
Venue: 
Hewlett 201

Applied Physics/Physics Colloquium

Topic: 
Dirac Composite Fermion in Quantum Hall Fluids
Abstract / Description: 

The fractional quantum Hall fluids are some of the most nontrivial strongly correlated states of matter. Existing theories of the fractional quantum Hall effect relies on the notion of the composite fermion. A long-standing problem of existing theories of the composite fermion is the lack of particle-hole symmetry of the lowest Landau level. I will describe how the particle-hole symmetry took a central role in recent theoretical discussions of the fractional quantum Hall effect; in particular, how a recent synthesis, motivated by the physics of graphene and topological insulators, has led to a new understanding of the low-energy quasiparticle of the half-filled Landau level. According to the new picture, the composite fermion is a Dirac particle with a nontrivial pi Berry phase around the Fermi surface. Distinctive consequences of the new proposal are outlined.


 

Held Tuesdays at 4:30 pm in the William R. Hewlett Teaching Center, room 201.

Refreshments in the lobby of Varian Physics at 4:15 pm.

Spring 2015/2016, Committee: M. Schleier-Smith (Chair), G. Gratta, B. Lev, S. Zhang

Date and Time: 
Tuesday, May 10, 2016 - 4:30pm to 5:30pm
Venue: 
Hewlett 201

Applied Physics/Physics Colloquium

Topic: 
Optical Atomic Clock and Many-body Quantum Physics
Abstract / Description: 

The relentless pursuit of spectroscopy resolution has been a key drive for many scientific and technological breakthroughs over the past century, including the invention of laser and the creation of ultracold matter. Our state-of-the-art laser now maintains optical phase coherence over multiple seconds and provides this piercing resolution across the entire visible spectrum. The new capability in control of light has enabled us to create and probe novel quantum matter via manipulation of dilute atomic and molecular gases at ultralow temperatures. For the first time, we control the quantum states of more than 1000 atoms so precisely that we achieve a more stable and accurate atomic clock than any existing atomic clocks, with both key clock characteristics reaching the 10-18 level. We use this precision measurement capability to explore novel many-body quantum states with the aim to develop the new frontier of quantum metrology. Such advanced clocks will allow us to test the fundamental laws of nature and enable a wide range of technological applications.


 

Held Tuesdays at 4:30 pm in the William R. Hewlett Teaching Center, room 201.

Refreshments in the lobby of Varian Physics at 4:15 pm.

Spring 2015/2016, Committee: M. Schleier-Smith (Chair), G. Gratta, B. Lev, S. Zhang

Date and Time: 
Tuesday, May 3, 2016 - 4:30pm to 5:30pm
Venue: 
Hewlett 201

Applied Physics/Physics Colloquium

Topic: 
Frontiers in Laser Spectroscopy
Abstract / Description: 

Optical frequency combs are providing powerful tools for laser spectroscopy. Mode-locked femtosecond lasers and related emerging miniaturized devices can produce a large number of precisely evenly spaced spectral lines. Almost two decades ago, such spectral combs were introduced as tools for optical frequency metrology, motivated by the challenges of precision laser spectroscopy of atomic hydrogen as tests for fundamental physics laws. Current precision spectroscopy of hydrogen with frequency combs focuses on the "proton size puzzle", i.e. the discrepancy between the rms proton charge radius determined from Lamb shift measurements in ordinary hydrogen and in muonic hydrogen. Laser frequency combs provide the long-missing clockwork for optical atomic clocks, which are now approaching relative frequency uncertainties of 10-18. Distant clocks can be compared via optical fiber links at the 10-19 level, opening new opportunities for relativistic geodesy and astronomical interferometry. Frequency combs in space will permit new tests of Einstein's equivalence principle. As calibration tools for astronomical spectrographs, frequency combs are facilitating the search for exoplanets, and they may lead to direct evidence for the accelerating expansion of space in our universe. Laser combs are also enabling novel broadband molecular spectroscopy. They can dramatically improve the resolution and recording speed of Fourier spectrometers, and they are creating intriguing new opportunities for highly multiplexed nonlinear spectroscopy and microscopy.


 

Held Tuesdays at 4:30 pm in the William R. Hewlett Teaching Center, room 201.

Refreshments in the lobby of Varian Physics at 4:15 pm.

Spring 2015/2016, Committee: M. Schleier-Smith (Chair), G. Gratta, B. Lev, S. Zhang

 

 
 
Date and Time: 
Tuesday, April 26, 2016 - 4:30pm to 5:30pm
Venue: 
Hewlett 201

Applied Physics/Physics Colloquium

Topic: 
The Uncanny Physics of Superhero Comic Books
Abstract / Description: 

In 2001 I created a Freshman Seminar class at the University of Minnesota entitled: "Everything I Know About Science I Learned from Reading Comic Books." This is a real physics class, that covers topics from Isaac Newton to the transistor, but there's not an inclined plane or pulley in sight. Rather, ALL the examples come from superhero comic books, and as much as possible, those cases where the superheroes get their physics right!

This class drew a great deal of media attention in 2002 with the release of the first Spider-Man film, and led to my writing a popular science book THE PHYSICS OF SUPERHEROES. My talk will show how superhero comic books can be used to illustrate fundamental physics principles. For example, was it "the fall" or "the webbing" that killed Gwen Stacy, Spider-Man's girlfriend in the classic Amazing Spider-Man # 121? How does Kitty Pryde from the X-Men comics and movies use quantum mechanics to walk through walls? Why does the Flash become heavier as he tries to run at the speed of light? All this, and the answers to such important real life questions as the chemical composition of Captain America's shield, and who is faster: Superman or the Flash? will be discussed. In my presentation I will describe the various ways that students' interest in these four-color adventurers can be leveraged to present real science in an accessible way. If superheroes can spark an interest in science in students and the general public – well, it wouldn't be the first time these heroes have saved the day!


 

Held Tuesdays at 4:30 pm in the William R. Hewlett Teaching Center, room 201.

Refreshments in the lobby of Varian Physics at 4:15 pm.

Spring 2015/2016, Committee: M. Schleier-Smith (Chair), G. Gratta, B. Lev, S. Zhang

Date and Time: 
Tuesday, April 12, 2016 - 4:30pm to 5:30pm
Venue: 
Hewlett 201

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