## Events

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# The David and Edith Harris Physics Colloquium Series

## SPRING 2018 Schedule

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

**Other Colloquia:**

Center for Theoretical Physics Colloquia and Seminars

Center for Ultracold Atoms Seminars (CUA)

Chez Pierre Seminars in Condensed Matter Physics at MIT

LNS Nuclear and Particle Physics Colloquia

Modern Optics and Spectroscopy Seminars

**MARCH 1, 2018**

**ELI ZELDOV
**Weizmann Institute of Science

Host: Leonid Levitov

"Nanoscale Thermal Imaging: Glimpse into Dissipation in Quantum Systems Down to Atomic Scale"

Energy dissipation is a fundamental process governing the dynamics of classical and quantum systems. Despite its vital importance, direct imaging and microscopy of dissipation in quantum systems is currently impossible because the existing thermal imaging methods lack the necessary sensitivity and are unsuitable for low temperature operation. We developed a scanning nanoSQUID that resides at the apex of a sharp pipette acting simultaneously as nanomagnetometer with single spin sensitivity and as nanothermometer providing cryogenic thermal imaging with four orders of magnitude improved thermal sensitivity of below 1 µK [Nature 539, 407 (2016)]. The non-contact non-invasive thermometry allows thermal imaging of minute energy dissipation down to the level equivalent to the fundamental Landauer limit for continuous readout of a single qubit. These advances enable observation of changes in dissipation due to single electron charging of a quantum dot and visualization and control of heat generated by electrons scattering off a single atomic defect in graphene [Science 358, 1303 (2017)], opening the door to direct imaging and spectroscopy of dissipation processes in quantum systems.

Time: 4:00 pm

Place: Room 10-250

Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

**MARCH 8, 2018**

**LICIA VERDE
**Catalan Institution for Research and Advanced Studies and Institute of Cosmological Sciences, University of Barcelona

Host: Salvatore Vitale

"Unconscious Bias…in Cosmology"

The standard cosmological model has been established and its parameters are now measured with unprecedented precision. However, there is a big difference between modelling and understanding. The next decade will see the era of large surveys; a large coordinated effort of the scientific community in the field is on-going to map the cosmos producing an exponentially growing amount of data. This will shrink the statistical errors.

But precision is not enough: accuracy is also crucial. Accuracy is very difficult to assess, and residual biases may remain. Systematic effects may be in the data but may also be in the model used in their interpretation. I will present a small selection of examples where I explore approaches to help the transition from precision to accurate cosmology. This selection is not meant to be exhaustive or representative, it just covers some of the problems I have been working on recently.

Time: 4:00 pm

Place: Room 10-250

Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

**MARCH 15, 2018**

**MONIKA SCHLEIER-SMITH
**Stanford University

Host: MIT Graduate Women in Physics

"Interfacing Spins with Photons for Quantum Simulation and Quantum Control"

The hallmark of quantum information is its capacity to be non-local, woven into correlations among two, three, or many entangled particles. By contrast, the interactions between particles are necessarily local, restricting the types of quantum states that appear in nature. Nevertheless, non-local interactions feature in a wide range of conceptual models, from spin models encoding hard optimization problems to toy models of quantum gravity and information scrambling in black holes. Motivated by prospects for exploring these concepts in the laboratory, I will present recent progress in engineering and probing effectively non-local interactions in experiments with cold atoms, with photons serving as messengers conveying information between them.

Time: 4:00 pm

Place: Room 10-250

Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

**MARCH 22, 2018**

**FERYAL OZEL
**University of Arizona

Host: Deepto Chakrabarty

"Neutron Star Interiors from All Angles"

The new era of multimessenger astronomy has substantially boosted studies of neutron stars. Timing of radio pulsars has produced precise neutron star masses and holds the promise of a moment-of-inertia measurement. X-ray observations of accreting neutron stars led to the first tight constraints on their radii. The first detection of gravitational waves from coalescing double neutron stars with LIGO already yielded information about their tidal deformability. In this talk, I will describe a framework that allows us to combine this trove of multimessenger information to measure the equation of state of neutron star matter. I will show that all current data point toward small (~11 km) radii for neutron stars. I will discuss the implications of these results for nuclear physics as well as the prospects of improving these measurements in the near future.

Time: 4:00 pm

Place: Room 10-250

Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

**APRIL 5, 2018**

**RAINER WEISS
**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)

**APRIL 12, 2018**

**JIAN-WEI PAN
**University of Science and Technology of China

Host: MIT Physics Graduate Student Council

"Breaking the Wall to Quantum Engineering"

Over the past three decades, the promises of super-fast quantum computing and secure quantum cryptography have spurred a world-wide interest in quantum information, generating fascinating quantum technologies for coherent manipulation of individual quantum systems. However, the distance of fiber-based quantum communications is limited due to intrinsic fiber loss and decreasing of entanglement quality. Moreover, probabilistic single-photon source and entanglement source demand exponentially increased overheads for scalable quantum information processing. To overcome these problems, we are taking two paths in parallel: quantum repeaters and through satellite. Based on these techniques, we are developing quantum repeaters that combine entanglement swapping, entanglement purification, and quantum memory for the ultra-long distance quantum communication. The second line is satellite-based global quantum communication, taking advantage of the negligible photon loss and decoherence in the atmosphere. The quantum science satellite 'Micius' was launched in 2016, and accomplished High-rate QKD between satellite and ground, quantum entanglement distribution from satellite and quantum teleportation from ground to satellite, for the first time. We are also making efforts toward the generation of multiphoton entanglement and its use in teleportation of multiple properties of a single quantum particle, topological error correction, quantum algorithms for solving systems of linear equations and machine learning, and high-efficiency multiphoton boson sampling.

Time: 4:00 pm

Place: Room 10-250

Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

**APRIL 19, 2018**

**GREGORY FALKOVICH
**Weizmann Institute of Science

Host: Leonid Levitov

"What Drives Weather Changes?"

Winds are driven by the gradients of solar heating. Vertical gradients cause thermal convection on the scale of the troposphere depth (less than 10 km). Horizontal gradients excite motions on a planetary (10000 km) and smaller scales. Weather is mostly determined by the flows at intermediate scale (hundreds of kilometers). Where do these flows get their energy from? The puzzle is that three-dimensional small-scale motions cannot transfer energy to larger scales while large-scale planar motions cannot transfer energy to smaller scales. In the talk, I will describe experimental and observational data that suggest one possible resolution to this puzzle. I will also describe some puzzling properties of two-dimensional turbulence including conformal invariance of statistics.

Time: 4:00 pm

Place: Room 10-250

Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

**APRIL 26, 2018**

**KATE SCHOLBERG
**Duke University

Host: Yen-Jie Lee

Title and abstract to be posted.

Time: 4:00 pm

Place: Room 10-250

Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

**MAY 3, 2018**

**DANIEL RALPH
**Cornell University

Host: Ray Ashoori

"Putting the Electron's Spin to Work"

In addition to carrying a quantized electrical charge, electrons also possess a quantized angular momentum, or spin. In ordinary charge-based electronics, the spins are usually randomly oriented and they do not play a role in device function. However, in the last ten years there have been significant advances in understanding of how to control electron spins in useful ways. Spin currents can now be used, for example, to apply torques within magnetic memory devices that are more than 1000 times stronger than charge-current-generated magnetic fields. I will discuss some of this progress, with an emphasis on recent discoveries that magnetic devices can be manipulated with record-breaking efficiencies using strong spin-orbit coupling in heavy metals and topological insulators.

Time: 4:00 pm

Place: Room 10-250

Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

**MAY 10, 2018**

**JOSHUA FRIEMAN
**University of Chicago

Host: Paul Schechter

"Probing Cosmology with the Dark Energy Survey"

I will give an overview of the Dark Energy Survey (DES) project and highlight its early science results, focusing on cosmology results from the first year of the survey. The DES collaboration built the 570-megapixel Dark Energy Camera for the Blanco 4-meter telescope at NOAO's Cerro Tololo Inter-American Observatory in Chile to carry out a deep, wide-area, multi-band optical survey of several hundred million galaxies and a time-domain survey to discover several thousand supernovae. The survey started in Aug. 2013 and will finish in 2018. DES was designed to address the questions: why is the expansion of the Universe speeding up? Is cosmic acceleration due to dark energy or does it require a modification of General Relativity? DES is addressing these questions by measuring the history of cosmic expansion and the growth of structure through multiple complementary techniques: galaxy clusters, the large-scale galaxy distribution, weak and strong gravitational lensing, and supernovae, as well as through cross-correlation with other data sets. I will also discuss how the DES data are being used to make a variety of other astronomical discoveries, from the outer Solar System to ultra-faint dwarf galaxies around the Milky Way to the first kilonova counterpart of a binary neutron star gravitational-wave source.

Time: 4:00 pm

Place: Room 10-250

Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

### PAST SPRING 2018 COLLOQUIA

**FEBRUARY 8, 2018**

**JENNIFER HOFFMAN
**Harvard University

Host: The MIT Society of Physics Students

"The Strong and the Weak Collide: The Cuprate Quantum Phase Transition"

In contrast to the band theory at the heart of the semiconductor revolution, where electrons can be treated individually despite their density, many exotic properties of today’s forefront materials stem from strong electronic interactions, that preclude single particle interpretation. Cuprates are a paradigmatic example, where strong interactions give rise to an array of exotic states and broken symmetries, including high-temperature superconductivity. It has been proposed that that this complex phase diagram is controlled by a quantum phase transition in the midst of superconductivity. To address the nature of the governing electronic interactions, we use atomically-resolved scanning tunneling spectroscopy to image an electronic density wave across the critical doping. We discover a reorganization of the electronic structure that abruptly shifts the density wave mechanism from strong to weak coupling physics. Furthermore, while the change of the underlying physics is sudden, the wavelength of the density wave evolves smoothly. This last observation points to a new paradigm to understand the quantum phase transition and the import of strong interactions in the cuprates.

Time: 4:00 pm

Place: Room 10-250

Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

**FEBRUARY 15, 2018**

**RAPHAEL BOUSSO
**University of California, Berkeley

Host: Daniel Harlow

"Black Holes, Quantum Information, and Unification"

The study of black holes has revealed a deep connection between quantum information and spacetime geometry. Its origin must lie in a quantum theory of gravity, so it offers a valuable hint in our search for a unified theory. Precise formulations of this relation recently led to new insights in Quantum Field Theory, some of which have been rigorously proven. An important example is our discovery of the first universal lower bound on the local energy density. The energy near a point can be negative, but it is bounded below by a quantity related to the information flowing past the point.

Time: 4:00 pm

Place: Room 34-101 NOTE: ROOM CHANGE

Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

**FEBRUARY 22, 2018**

**LORENZO SIRONI
**Columbia University

Host: Nuno Loureiro

"Fast and Furious: Magnetic Reconnection in Relativistic Jets and Black Hole Coronae"

Relativistic blazar jets and black hole coronae routinely display fast and bright flares of non-thermal emission. By means of fully-kinetic particle-in-cell (PIC) simulations, we show that magnetic reconnection in the relativistic regime appropriate for blazar jets (i.e., at magnetizations sigma>>1) can satisfy all the basic conditions for the emission: extended non-thermal distributions of accelerated particles (with power-law slope between -4 and -1), efficient dissipation and rough equipartition between particles and magnetic field in the emitting region. In addition, we show that ultra-relativistic plasmoids generated by reconnection can power the ultra-fast bright flares observed from a number of TeV blazars. We also discuss electron heating and non-thermal acceleration in the trans-relativistic regime sigma~1 appropriate for the magnetized coronae of collisionless accretion flows, like Sgr A* at the center of our Galaxy.

Time: 4:00 pm

Place: Room 10-250

Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

*Last updated on February 23, 2018 10:28 AM*