Applied Physics / Physics Colloquium

Applied Physics/Physics Colloquium

Topic: 
Frontiers in Quantum Many-body Physics and Neuromorphic Computation with Multimode Cavity QED
Abstract / Description: 

Investigations of many-body physics in an AMO context often employ a static optical lattice to create a periodic potential. Such systems, while capable of exploring, e.g., the Hubbard model, lack the fully emergent crystalline order found in solid state systems whose stiffness is not imposed externally, but arises dynamically. Our multimode cavity QED experiment will introduce a new method of generating fully emergent and compliant optical lattices supporting phonon-like excitations to the ultracold atom toolbox. The system provides new avenues to explore quantum liquid crystalline order. We will report experimental progress, including our recent observation of a "supermode-density-wave-polariton condensate." Future employment of spinful atoms will provide opportunities to explore quantum neural networks and the order of short-range spin glasses.

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

Applied Physics/Physics Colloquium

Topic: 
How to Detect A Gravitational Wave: A discussion about the Advanced LIGO Interferometers
Abstract / Description: 

On September 14th, 2015, the twin detectors of the Advanced Laser Interferometer Gravitational-wave Observatory (LIGO) made the first direct measurement of a passing gravitational wave. The signal was generated by the merger of two black holes which were approximately 29 and 36 solar masses. Although the event released about 3 solar masses of energy in a fraction of a second, when the signal reached the earth the distortion from the wave only changed the length of the 4 km long LIGO detectors by about 4e-18 meters. This was considered a large signal, with a signal-to-noise ratio of 24. In this talk, I will describe the remarkable instruments used for this detection, and discuss the plans to move forward so that these detectors can be regular contributors to the field of astronomy.

Date and Time: 
Monday, March 28, 2016 - 4:15pm to 5:15pm
Venue: 
Spilker 232

Applied Physics/Physics Colloquium

Topic: 
A New View of the High Energy Universe: Science Highlights from the Nuclear Spectroscope Telescope Array (NuSTAR) Mission
Abstract / Description: 

The Nuclear Spectroscopic Telescope Array, the first focusing high-energy X-ray (3-79 keV) telescope in orbit, extends sensitive X-ray observations above the band pass where Chandra and XMM-Newton operate. With an unprecedented combination of sensitivity, spectral and imaging resolution above 10 keV, NuSTAR is advancing our understanding of black holes, neutron stars, and supernova remnants. Harrison will describe the mission, and present science highlights to-date spanning from probing the regions within a few gravitational radii of black holes to understanding the mechanisms that make massive stars explode.

Date and Time: 
Tuesday, March 29, 2016 - 4:30pm to 5:30pm
Venue: 
Hewlett 201

Program in History and Philosophy of Science presents "Gaining Access to the Early Universe"

Topic: 
Gaining Access to the Early Universe
Abstract / Description: 

Theories allow us to use accessible data to answer questions about other domains. In the initial stages of inquiry, a theory is often accepted based on its promise for extending our epistemic reach in this sense. Using theory to gain access to unobserverable phenomena poses an obvious risk of circularity: the theory specifies dependencies that hold between data and the target phenomena, and the data provide evidence when interpreted in light of the theory. How does the successful use of the theory to gain access support the theory itself? Demanding strong evidence at the outset, to even accept a theory as a starting point for inquiry, would be counter-productive. Detailed evidence for the theory can best be obtained by exploiting the theory in ongoing research. I will argue that physicists often accept a theory as the basis for research in this sense, and consider how they respond to the risk of circularity. The crucial question regards whether the fundamental assumptions of the theory can be subjected to further tests. These tests are needed to justify taking a theory to capture the fundamental quantities and physical laws, rather than being merely compatible with a given body of data. I will consider how these general questions are reflected in early universe cosmology. I will argue that there are two distinctive obstacles to testing inflationary cosmology: (1) lack of sufficient theoretical constraints ("anything goes"); (2) lack of independent observational and experimental access. The second point reflects our practical limitations. I take the first point, however, as grounds for drawing a distinction between inflation and earlier physical theories: eternal inflation, in particular, undercuts the possibility of subjecting the fundamental assumptions of the theory to further tests.

Date and Time: 
Thursday, March 3, 2016 - 4:30pm to 5:30pm
Venue: 
History Room 205

Applied Physics/Physics Colloquium

Topic: 
Cortical Vision from Emergent Global Dynamics
Abstract / Description: 

The confusing thicket of connections between neurons renders the brain a complex system. We have embarked on deducing how the subjective experience of vision emerges from the interaction of billions of neurons. Picking up mathematical tools from established studies of complexity, we infer network properties from the statistics of neural activity in cerebral cortex during visual processing. Specifically, I will present evidence for the notion that brain circuits self-organize to operate at a point of optimized signal processing, including during intense visual stimulation.


 

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

Winter 2015/2016, Committee: R. Blandford (Chair), T. Heinz, L. Hollberg, K. Irwin

 

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

Applied Physics/Physics Colloquium

Topic: 
Effective Field Theory in Cosmology
Abstract / Description: 

Observational cosmology has made tremendous progress in the last couple of decades, allowing us to explore the beginning of the universe with unprecedented precision. Such exquisite measurements have now made us sensitive to non-linear corrections to the evolution of the density perturbations. In order to continue to address the mysteries of our universe with similar success, we have to be able to control these non-linearities. In this context, the effective field theory paradigm, which has been widely used in the context of particle physics, represents the ideal setup to explore and systematically study the signatures that come from interactions, and additionally to directly map what we are learning from data into theory. I will describe two recent applications of this paradigm to Cosmology: the Effective Field Theory of Inflation and the Effective Field Theory of Cosmological Large Scale Structures (EFTofLSS). The first example represents the general parametrization of fluctuations around an inflationary background, the earliest phase of our universe, and it allows us to study its most general signatures. The second example is in the context of the gravitational clustering of matter. In our universe matter perturbations are large on short distances and small on long distances: strongly coupled in the UV and weakly coupled in the IR. We formulate an effective description based on an IR fluid-like system that allows us to develop a perturbative expansion to describe weak matter clustering. I will discuss the formalism, the main results and successes so far, and how this research program is crucial for next generation cosmological experiments.


 

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.

 

Winter 2015/2016, Committee: R. Blandford (Chair), T. Heinz, L. Hollberg, K. Irwin

Date and Time: 
Tuesday, January 19, 2016 - 4:30pm to 5:30pm
Venue: 
Hewlett 201

Applied Physics/Physics Colloquium

Topic: 
Black Holes from Cosmic Inflation
Abstract / Description: 

Spherical domain walls and vacuum bubbles can spontaneously nucleate and expand during the inflationary epoch in the early universe. After inflation ends, the walls and/or bubbles form black holes with a wide spectrum of masses. For some parameter values, the black holes can serve as dark matter or as seeds for supermassive black holes at galactic centers. This mechanism of black hole formation is very generic and has important implications for the global structure of the universe. Black holes with mass greater than certain critical value contain inflating universes inside. The resulting multiverse has a very nontrivial spacetime structure, with a multitude of eternally inflating regions connected by wormholes.


 

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.

 

Winter 2015/2016, Committee: R. Blandford (Chair), T. Heinz, L. Hollberg, K. Irwin

Date and Time: 
Tuesday, March 8, 2016 - 4:30pm to 5:30pm
Venue: 
Hewlett 201

Applied Physics/Physics Colloquium

Topic: 
Electromechanics: A New Quantum Technology
Abstract / Description: 

Devices that combined electricity with moving parts were crucial to the very earliest electronic communications. Today, electromechanical structures are ubiquitous yet under-appreciated signal processing elements. Because the speed of sound is so slow compared to the speed of light, they are used to create compact filter and clock elements. Moreover they convert force and acceleration signals into more easily processed electrical signals. Can these humble, apparently classical, objects exhibit genuinely quantum behavior? Indeed-by strongly coupling the vibrations of a micromechanical oscillator to microwave frequency electrical signals, a mechanical oscillator can inherit a quantum state from an electrical signal. This recent and exciting result heralds the development of a quantum processors or quantum enhanced sensors that exploit the unique properties of mechanical systems. Furthermore, quantum electromechanics provides a powerful and versatile way to bring ever larger, more tangible objects into non-classical 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.

 

Winter 2015/2016, Committee: R. Blandford (Chair), T. Heinz, L. Hollberg, K. Irwin

Date and Time: 
Tuesday, March 1, 2016 - 4:30pm to 5:30pm
Venue: 
Hewlett 201

Applied Physics/Physics Colloquium

Topic: 
The Genesis of General Relativity and its Formative Years
Abstract / Description: 

The conceptual revolution that Einstein started in 1907, when he introduced the equivalence principle and began his search for a comprehensive theory describing gravitation and inertia within a relativistic framework, was completed with the publication, on November 25, 1915, of his general theory of relativity. Immediately after its publication the theory was elaborated and controversially discussed by physicists, mathematicians, astronomers, and philosophers. During these formative years, the basic ideas and principles were refined, the first solutions of the field equations were derived and analyzed, and the cosmological consequences of the theory were debated. Einstein himself made further fundamental contributions to the development of his theory, exploring its consequences such as gravitational waves and cosmological models, and reinterpreting basic aspects of the theory.

On the hundredth anniversary of Einstein's monumental achievement, it is natural to look back at what we are celebrating and address such questions as: What guided Einstein on his road to general relativity? What guidelines had to be re-examined and even abandoned? Why did it take him eight years? Why did he reject every suggestion of an expanding universe? Why did he introduce the cosmological constant and why did he remove it? The lecture will describe Einstein's unique scientific odyssey, exploring these and other questions.


 

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.

 

Winter 2015/2016, Committee: R. Blandford (Chair), T. Heinz, L. Hollberg, K. Irwin

Date and Time: 
Tuesday, February 23, 2016 - 4:30pm to 5:30pm
Venue: 
Hewlett 201

Applied Physics/Physics Colloquium

Topic: 
On the Measurement of Gravitational Waves from the Merger of two Black Holes
Abstract / Description: 

Over a billion years ago, a binary black hole system enjoyed its last few orbits and collided, releasing three solar masses worth of energy into vibrations of spacetime: gravitational waves.

​Towards the end of the summer of 2015, the ​LIGO team was wrapping up the final touches on the recent upgrades to their interferometers and getting it ready to run. Early in the morning on September 14th, those waves from a billion years ago rippled through the earth and were recorded by the LIGO detectors.

This is the story of those waves and detectors.


 

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

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

 

Winter 2015/2016, Committee: R. Blandford (Chair), T. Heinz, L. Hollberg, K. Irwin

Date and Time: 
Tuesday, February 16, 2016 - 4:30pm to 5:30pm
Venue: 
Hewlett 200

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