The David and Edith Harris Physics Colloquium Series

SPRING 2016 Schedule

Thursdays - Socials: 3:30pm in 4-349 (The Pappalardo Room) // Talk: 4:00pm in 10-250 (unless otherwise noted)

FEBRUARY 4, 2016
DAN HARLOW
Harvard University
Host: Hong Liu

"Bulk Locality from Quantum Error Correction in AdS/CFT"

The Anti-de Sitter/Conformal Field Theory correspondence has given us a non-perturbative description of quantum gravity in asymptotically Anti-de Sitter space, as a quantum field theory (without gravity) living in one lower dimension. This proposal has passed many tests, but the emergence of the extra dimension has remained somewhat mysterious. In this talk I will discuss recent work relating this emergence to the theory of quantum error correcting codes, originally introduced to solve the seemingly unrelated problem of protecting a quantum computer from decoherence. I'll introduce some puzzles in AdS/CFT that are naturally resolved in this language. We will also see that it makes precise some recent speculations relating boundary entanglement to the emergence of bulk geometry. I will illustrate these ideas using an explicitly soluble model of AdS/CFT, constructed using tensor networks. The talk should be quite accessible to beginning graduate students!

Time: 4:00 pm
Place: Room 10-250
Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

FEBRUARY 11, 2016
ZHENG-TIAN LU
University of Science and Technology of China
Host: Yen-Jie Lee

"Atom Trap, Krypton-81, and Global Groundwater"

The long-lived noble-gas isotope 81Kr is the ideal tracer for water and ice with ages of
105 - 106 years, a range beyond the reach of 14C. 81Kr-dating, a concept pursued over the past five decades, is finally available to the earth science community at large. This is made possible by the development of the Atom Trap Trace Analysis (ATTA) method, in which individual atoms of the desired isotope are captured and detected. ATTA possesses superior selectivity, and is thus far used to analyze the environmental radioactive isotopes 81Kr, 85Kr, and 39Ar. These three isotopes have extremely low isotopic abundances in the range of 10-16 to 10-11, and cover a wide range of ages and applications. In collaboration with earth scientists, we are dating groundwater and mapping its flow in major aquifers around the world. We have also demonstrated for the first time 81Kr-dating of old ice.

Time: 4:00 pm
Place: Room 34-101 (NOTE ROOM CHANGE)
Refreshments @ 3:30 pm in 34-101 lobby (NOTE ROOM CHANGE)

FEBRUARY 18, 2016
ZOHAR KOMARGODSKI
Weizmann Institute of Science
Host: Hong Liu

“Second-Order Phase Transitions and Conformal Field Theories”

We review some recent progress on the long-standing problem of characterizing second-order phase transitions. The symmetries of second-order transitions are now better understood. In addition, there are new general results about critical exponents, a better control of what happens when relevant operators are turned on, and some constraints on higher correlation functions. These new ideas can be tested in systems ranging from boiling water to quantum gravity in Anti-de Sitter space.

Time: 4:00 pm
Place: Room 10-250
Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

FEBRUARY 25, 2016
RAINIER WIESS
MIT
Host: Peter Fisher

Title and abstract to be posted.

Time: 4:00 pm
Place: Room 10-250
Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

MARCH 3, 2016
SHEP DOELEMAN

MIT Haystack Observatory
Host: Scott Hughes

"The Event Horizon Telescope: Imaging and Time-Resolving a Black Hole"

A convergence of high bandwidth radio instrumentation and Global mm and submm wavelength facilities are enabling assembly of the Event Horizon Telescope (EHT): a short-wavelength Very Long Baseline Interferometry (VLBI) array, which can observe the nearest supermassive black holes with Schwarzschild Radius resolution. Initial observations with the EHT have revealed event horizon scale structure in SgrA*, the 4 million solar mass black hole at the Galactic Center, and in the much more luminous and massive black hole at the center of the giant elliptical galaxy M87. Over the next 2 years, this international project will add new sites and increase observing bandwidth to focus on astrophysics at the black hole boundary. The EHT will have an unprecedented combination of sensitivity and resolution with excellent prospects for imaging strong GR signatures near the horizon, detecting magnetic field structures through full polarization observations, time-resolving black hole orbits, testing GR, and modeling black hole accretion, outflow and jet production. This talk will describe the project and the latest EHT observations.

Time: 4:00 pm
Place: Room 10-250
Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

MARCH 10, 2016
HARI MANOHARAN
Stanford University
Host: Ray Ashoori

Title and abstract to be posted.

Time: 4:00 pm
Place: Room 10-250
Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

MARCH 17, 2016
MICHAEL DESAI
Harvard University
Host: Jeff Gore

"Evolutionary Dynamics in Microbes"

The basic rules of evolution are well known: mutations generate variation, while genetic drift, recombination, and natural selection change the frequencies of the variants. Yet even in very simple and well-defined circumstances, it is often surprisingly difficult to predict what is possible in evolution, over what timescales and in which conditions. This is particularly true in microbial populations, where natural selection faces a key problem: there is too much going on at once. Many mutations are often present simultaneously, and selection cannot act on each individually. Rather, mutations are constantly occurring in a variety of combinations linked together on physical chromosomes, and selection can only act on these combinations as a whole. This dramatically changes how evolution can act. I will describe both theoretical and experimental worked aimed at understanding evolution in these populations.

Time: 4:00 pm
Place: Room 10-250
Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

MARCH 31, 2016
TBA
Host: TBA

Title and abstract to be posted.

Time: 4:00 pm
Place: Room 34-101 (NOTE ROOM CHANGE)
Refreshments @ 3:30 pm in 34-101 lobby (NOTE ROOM CHANGE)

APRIL 7, 2016
LISA RANDALL
Harvard University
Host: MIT Society of Physics Students

Title and abstract to be posted.

Time: 4:00 pm
Place: Room 10-250
Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

APRIL 14, 2016
NAI PHUAN ONG
Princeton University
Host: Joe Checkelsky

"Dirac Semimetals, Weyl States, and the Chiral Anomaly*"

A host of interesting electronic phenomena associated with the 2D Dirac states have been observed in graphene. The Dirac nodes in graphene are rigorously protected by time reversal symmetry (TRS) and inversion symmetry (IS). Starting in ~2012, interest turned to 3D Dirac materials. The combination of TRS, IS and point group symmetry leads to protected Dirac nodes, provided they lie on a high-symmetry axis. Predictions that the two semimetals Na3Bi and Cd3As2 are topological Dirac semimetals were quickly confirmed.

I will describe the successful growth and refinement of these materials, focusing on Na3Bi. The existence of Dirac states in 3+1 dimensions provide an exciting platform for searching for the chiral anomaly in a crystal. I will also briefly explain the chiral anomaly and its mysterious niche in quantum field theory, then describe its recent detection in Na3Bi. Spectral flow between Weyl states of opposite chiralities engenders an enhanced current plume that is locked to the direction of the applied magnetic field. I will outline a new approach that may turn up the chiral anomaly in strong spin-orbit-interaction, zero-gap semimetals which do not a priori have Dirac states in zero magnetic field (this is a large class). A strong magnetic field creates Weyl nodes. Again, the spectral flow in an electric field leads to the chiral anomaly. The thermoelectric properties of the chiral anomaly current are described.

*Supported by ARO, ARO-MURI, Moore Foundation and NSF.

Time: 4:00 pm
Place: Room 10-250
Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

APRIL 21, 2016
ALEXANDRA VON MEIER
California Institute for Energy and Environment
Host: Peter Fisher

Physics in the Interest of Society Colloquium

Title and abstract to be posted.

Time: 4:00 pm
Place: Room 10-250
Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

APRIL 28, 2016
SAVAS DIMOPOULOS
Stanford University
Host: Jesse Thaler

“Experiments Big and Small”

I will discuss explorations of fundamental physics via the LHC, as well as smaller experiments which may play a leading role in the future.

Time: 4:00 pm
Place: Room 34-101 (NOTE ROOM CHANGE)
Refreshments @ 3:30 pm in 34-101 lobby (NOTE ROOM CHANGE)

MAY 5, 2016
TILMAN PFAU
University of Stuttgart
Host: Martin Zwierlein

"Ultracold Dipolar Gases: From Chromium to Lanthanides”

Dipolar interactions in gases are fundamentally different from the usual van der Waals forces. Besides the anisotropy, the dipolar interaction is nonlocal and as such allows for self organized structure formation. Ten years ago, the first dipolar effects in a quantum gas were observed in an ultracold Chromium gas. By using a Feshbach resonance, a purely dipolar quantum gas was observed three years later. Currently, dipolar interaction effects have been observed in lattices and also polar molecules. Recently, it became possible to study degenerate gases of lanthanide atoms among which one finds the most magnetic atoms. The recent observation of their collisional properties include the emergence of quantum chaos and very broad resonances. Similar to the Rosensweig instability in classical magnetic ferrofluids, a self organized structure formation was expected. In our experiments with quantum gases of Dysprosium atoms we have recently observe the formation of a droplet crystal. In contrast to theoretical mean field based predictions the superfluid droplets did not collapse. We find that this unexpected stability is due to beyond mean field quantum corrections of the Lee-Huang-Yang type.

Time: 4:00 pm
Place: Room 10-250
Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

Last updated on February 4, 2016 9:35 AM