Applied Physics / Physics Colloquium

From Planck to Escher [Applied Physics/Physics Colloquium]

Topic: 
From Planck to Escher
Abstract / Description: 

The recent observational data from the Planck satellite and ground based experiments support the standard cosmological model, defined by just a few independent parameters. Two of them require a theoretical explanation: the tilt of the power spectrum of the inflationary CMB fluctuations ns, and the level of inflationary gravitational waves, B-modes, r< 0.07. I will describe the recently developed class of inflationary models based on the Poincare disk model of hyperbolic geometry, which is beautifully represented by the Escher's picture Circle Limit IV. In such models, ns is very close to the Planck result ns =0.965, whereas the amplitude of the gravitational waves can take various values proportional to the square of the radius of the Poincare disk. These models predict seven distinct targets for the B-mode experiments in the range r = 10-2 -10-3, motivated by string theory.


 

Held Tuesdays at 4:30 pm in the William R. Hewlett Teaching Center, room 200. Refreshments in the lobby of Varian Physics at 4:15 pm.

Winter 2016/2017, Committee: A. Linde (Chair), S. Kivelson, S. Zhang

Date and Time: 
Tuesday, March 14, 2017 - 4:30pm
Venue: 
Hewlett 200

Cosmology and the Arrow of Time [Applied Physics/Physics Colloquium]

Topic: 
Cosmology and the Arrow of Time
Abstract / Description: 

The distinction between the past and the future has long been a puzzle. The world around us displays a huge asymmetry between the two directions of time, with eggs that easily break but never reassemble. However, according to the known laws of physics, for every system that evolves in time, there exists in principle a time-reversed (i.e., CPT conjugate) state that evolves in exactly the same way, but backwards in time. The time asymmetry is often attributed to the assumption that the universe began in a very low entropy state. This explanation is satisfactory, but leaves open the question of why the universe started in a low entropy state. In this talk I will describe a new picture of spacetime, proposed in 2004 by Carroll and Chen, in which the arrow of time can be explained by using only time-symmetric laws of physics and time-symmetric initial conditions as well.


 

Held Tuesdays at 4:30 pm in the William R. Hewlett Teaching Center, room 200. Refreshments in the lobby of Varian Physics at 4:15 pm.

Winter 2016/2017, Committee: A. Linde (Chair), S. Kivelson, S. Zhang

Date and Time: 
Tuesday, March 7, 2017 - 4:30pm
Venue: 
Hewlett 200

Probing the Electron to Test the Most Precise Prediction of the Standard Model and Beyond [Applied Physics/Physics Colloquium]

Topic: 
Probing the Electron to Test the Most Precise Prediction of the Standard Model and Beyond
Abstract / Description: 

The most precise measurement of an elementary particle property tests the Standard Model's most precise prediction. The electron's measured charge asymmetry probes well beyond the Standard Model.

Date and Time: 
Tuesday, February 28, 2017 - 4:15pm
Venue: 
Hewlett 200

Exploring the Landscape of Interacting Topological Insulators [Applied Physics/Physics]

Topic: 
Exploring the Landscape of Interacting Topological Insulators
Abstract / Description: 

The past decade has seen a phenomenal rise of topological insulators and superconductors. The first discovery, led by the Stanford group and the Wurzburg group, concerns a planar material of a "quantum spin Hall topological insulator," which acts as an electronic superhighway. It is one of the building blocks needed to create future electronics and computers. In this talk I will show, as proposed by the Stanford group, that such insulators can be built from common compound semiconductors containing a double-layer of electrons and holes, created by band-gap engineering using molecular beam epitaxy and electrostatic gates. The material supports quantized one dimensional helical edge modes. Quite surprisingly, here we find a superhighway with puzzling twists, for which electron-electron interactions may be responsible. Amazingly, due the interactions between electron and holes, our recent optical and transport experiment confirm that the material can become a superconductor, where the pairing of electron and holes resembles the Cooper pair in ordinary superconductors.

Reference: X. L. Qi,S. C. Zhang, Review of Modern Physics, 83(4), 175 (2010)

 

 

Date and Time: 
Tuesday, February 21, 2017 - 4:30pm
Venue: 
Hewlett 200

Quantum supremacy: Checking a quantum computer with a classical supercomputer [Applied Physics/Physics Colloquium]

Topic: 
Quantum supremacy: Checking a quantum computer with a classical supercomputer
Abstract / Description: 

A key step in the roadmap to build a scientifically or commercially useful quantum computer will be to demonstrate its exponentially growing computing power. I will explain how a 7 by 7 array of superconducting xmon qubits with nearest-neighbor coupling, and with programmable single- and two-qubit gate with errors of about 0.1%, can execute a modest depth quantum computation that fully entangles the 49 qubits. Sampling of the resulting output can be checked against a classical simulation to demonstrate proper operation of the quantum computer and compare its system error rate with predictions. With a computation space of 2^49 = 5 x 10^14 states, the quantum computation can only be checked using the biggest supercomputers. With modest improvements in qubit performance, we plan to demonstrate this experiment in 2017.

Date and Time: 
Tuesday, February 14, 2017 - 4:30pm
Venue: 
Hewlett 200

Symmetries, Duality, and the Unity of Physics [Applied Physics/Physics Colloquium]

Topic: 
Symmetries, Duality, and the Unity of Physics
Abstract / Description: 

Global symmetries and gauge symmetries have played a crucial role in physics. The idea of duality demonstrates that gauge symmetries can be emergent and might not be fundamental. During the past decades it became clear that the circle of ideas about emergent gauge symmetries and duality is central in different branches of physics, including condensed matter physics, quantum field theory, and quantum gravity. I will review these developments, which highlight the unity of physics.

Date and Time: 
Tuesday, February 7, 2017 - 4:30pm
Venue: 
Hewlett 200

The Direct Detection of Gravitational Waves: Observation of the Mergers of Black Hole Binaries [AP/Physics Colloquium]

Topic: 
The Direct Detection of Gravitational Waves: Observation of the Mergers of Black Hole Binaries
Abstract / Description: 

I will cover some of the history of gravitational waves and include a description of the instrument and the data analysis techniques. Measurement results and the prospects for the future will also be discussed.

Date and Time: 
Tuesday, January 24, 2017 - 4:30pm
Venue: 
Hewlett 200

Programming: A Medium for Clarifying Ideas [AP/Physics Colloquium]

Topic: 
Programming: A Medium for Clarifying Ideas
Abstract / Description: 

We think of computers as compliant slaves that deliver computational power in the same way that a power shovel delivers muscle power. To me programming is a medium for the expression and investigation of ideas, analogous to natural language and mathematics.

In subjects that I teach at MIT, such as advanced classical mechanics, it is easy to get a right answer without real understanding. I use computer programs to communicate a deeper understanding of the material. Programs are for students to read as well as for a computer to execute. Expressing methods in a computer language forces them to be unambiguous and computationally effective. The task of formulating a method as an executable program and debugging it is a powerful part of the learning process. Once formalized as a program, a mathematical idea becomes a tool that can be used to compute results.

I will show how programming can help us to illuminate subjects like Analytical Mechanics and Differential Geometry and make parts of General Relativity come alive.

Date and Time: 
Tuesday, January 17, 2017 - 4:15pm
Venue: 
Hewlett 200

Atomic Collapse in Graphene [AP/Physics Colloquium]

Topic: 
Atomic Collapse in Graphene
Abstract / Description: 

Since the discovery that electrons in graphene behave as massless Dirac fermions, the single-atom-thick material has become a fertile playground for testing exotic predictions of quantum electrodynamics, such as Klein tunneling and the fractional quantum Hall effect. Now add to that list atomic collapse, the spontaneous formation of electrons and positrons in the electrostatic field of a superheavy atomic nucleus. The atomic collapse was predicted to manifest itself in quasi-stationary states which have complex-valued energies and which decay rapidly. However, the atoms created artificially in laboratory have nuclear charge only up to Z = 118, which falls short of the predicted threshold for collapse. Interest in this problem has been revived with the advent of graphene, where, because of a large fine structure constant, the collapse is expected for Z of order unity. I will discuss the symmetry aspects of atomic collapse, in particular the anomalous breaking of scale invariance that underpins the collapse phenomenon. I will also describe recent experiments that use scanning tunneling microscopy (STM) to probe atomic collapse near STM-controlled artificial compound nuclei.

 

Presented by APPLIED PHYSICS/PHYSICS COLLOQUIUM
Professor Stanley S. Hanna Visiting Professorship Program

Date and Time: 
Tuesday, January 10, 2017 - 4:15pm to 5:30pm
Venue: 
Hewlett, Room 200

Applied Physics/Physics Colloquium: The Dawn of Gravitational-Wave Astrophysics

Topic: 
The Dawn of Gravitational-Wave Astrophysics
Abstract / Description: 

The very first observing run of the Advanced LIGO detectors led to the discovery of binary-black-hole inspiral and merger events, and overnight we got launched into the era of gravitational-wave astrophysics. In this talk I will review the key results from the recent LIGO data search, signal characterization, and measurements of source properties. I will discuss how this observation enables the first tests of general relativity in the strong-field regime and what this discovery implies for black-hole astrophysics.


 

Held Tuesdays at 4:30 pm in the William R. Hewlett Teaching Center, room 200. Refreshments in the lobby of Varian Physics at 4:15 pm.

Autumn 2016/2017, Committee: R. Blandford (Chair), A, Kapitulnik, R. Laughlin, L. Senatore

Date and Time: 
Tuesday, November 29, 2016 - 4:30pm to 5:30pm
Venue: 
Hewlett 200

Pages

Subscribe to RSS - Applied Physics / Physics Colloquium